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Embedded Systems and Design & Development - Feb 17, 2026 | Morning | VisionAstraa EV Academy

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This content provides a detailed overview of voltage sensing methods and their application within Battery Management Systems (BMS), particularly for electric vehicles (EVs), focusing on essential functions like monitoring and over-voltage protection.

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Yeah, good morning all of you

Just we had a little bit of uh technical

issues from my side. The microphone was

not working. That is why we couldn't

Okay. So in line with the discussions

what we had in the previous uh class, we

will have a discussion on some of the

aspects of battery management systems.

So the preliminary functions of a

battery management system is sensing

voltage, sensing current, sensing

temperature and trying to charge,

discharge the battery, keep the battery

safe and provide appropriate power. all

these functions. So the primary

requirement as stated starts with the

measurement of voltage and then the

current and then the temperature. So in

this session we will be looking into

what are the different ways we can uh

measure the voltage what different uh

sensors are available and when it comes

to processing the value acquired by the

voltage sensors what kind of uh uh

things we are supposed to note down and

uh how to uh use this information for

control purposes. For instance, we will

take uh in this session we will take

over voltage control and then we will

move on to other sorts of control aspects.

So there are variety of functions

performed by our BMS battery management

system that starts with battery

monitoring. So if we recolct the block

diagram of a hybrid electric vehicle

which we saw in the previous session, we

saw a block which said cell monitoring

CM cell monitoring. So this cell

monitoring is the one which monitors the

essential parameters of a battery cell

and we do have battery monitors. So

fundamentally it uh stream narrows down

to measurement of voltage that is cell

voltage battery cell voltage measurement

of the current whether it is charge

current or discharge current and

measurement of the thermal aspects of

our battery. So together these things

helps us to control the way in which the

battery is charged or discharged and to

So when it comes to cell monitoring, the

cell monitor primarily measures these

three parameters voltage, current,

temperature as we mentioned earlier. And

from this voltage and current obviously

we will be able to get a idea about the

power dealt by the battery. So we have

to make sure there are correct correct

mechanisms which are used for measuring

the cell wtages. Plenty of methods are

available. So one of these methods will

be used for measuring the cell voltage.

Now this information needs to be

provided to the embedded controller. So

now you have to remember that this

voltage which we are measuring is a

analog wtage.

This analog wtage the information should

be given to the embedded controller

which happens to be a digital device and

there is a signal type mismatch analog

on the input side that is a sensor data

side on the output side that is a

microcontroller sample controller side

you have the digital requirement. So

these two types have to be made

compatible. So that is where the signal

conditioning network comes in or you can

simply say it as interfacing circuit

comes in. So these interfacing circuit

does a lot of job starting from

converting the signal type so that the

input and output both of them becomes

compatible with the microcontroller and

then it processes the signal conditions

the signal for instance if at all there

is a magnitude mismatch. So this

magnitude mismatch is taken care by

these interfacing circuitry. Then

conditioning of the circuit if at all

there is a scope of noise to be present

in this measured signal. These noise has

to be removed before that is processed

or else the control will not be

reliable. So all these essential

functions are performed by the circuit

which are sitting in between the sensor

and the embedded controller. Now keeping

this aside for a moment, we will delve

deep into the different types of voltage

sensors which we can commonly come

across and the ones which are frequently

used in automotive industry especially

electric vehicles.

So there are different types which we

have listed on the screen. It starts

from a very simple potential divider

based voltage sensors. These are the

simplest of all voltage sensors and

these are the cheapest of all. Of

course, it comes with a trade-off. There

are certain limitations of using this

resistive voltage divider. And then we

have these capacitive voltage dividers.

Capacitive voltage based sensors. These

are essentially similar to resistive

voltage dividers in the manner that they

will have two capacitors connected in

series minimum two capacitors and the

potential drop created by these

capacitors are essentially used to

measure the voltage

and then the third type the

transformer-based voltage sensors. So

these essentially makes use of the

fundamental principles of electrical

engineering like Faraday's law. Then

they convert the high voltage into low

voltage. This low voltage is made

compatible with the embedded controller

input and thereby it is used to identify

the cell parameter cell voltage. In this

case that is a third type of sensors and

then we have the hall effect based

sensors. So now when we mention about

hall effect sensors we have to be little

bit more clear in understanding.

Basically these kinds of hall effect

sensors are based upon the hall effect.

So which says that when a current

carrying conductor is subjected to a

magnetic field a potential will be

developed across the opposite ends. So

these are 90° apart all these three

parameters. So measuring the potential

developed the potential which is called

as hull voltage. So measuring this

potential we will be able to understand

what amount of magnetic field is there

or what amount of current is flowing

through this hall element. So basically

these are either can be called as a

magnetic sensor or it can be called as a

current sensor. So when we make these

hall effect sensors in a closed loop

structure specialized circuit

arrangements they can in fact be used

for measuring voltages also. So

fundamentally in the general circuits

what we have seen we have come across

these hall of fit sensors as current

sensors or perhaps the ones which

measures the magnetic field kind of

magnetic proximity these kinds of

applications or what we would have seen.

So when they are fabricated properly

these hall effect sensors can be used

for measuring voltages also and this is

one of the primary sensors which are

used in EV industries. Of course not the

fundamental hall effect sensor a kind of

variant of this hall effect sensor in a

closed loop tuned closed loop and then

we have the other two versions which

comes as isolation amplifier based

voltage sensors and voltage monitoring

IC specific A6 application specific

integrated circuit which are designed

and fabricated for measuring the cell

voltages and other cell parameters. So

when we look into each and every one of

these types obviously we will be uh

wondering how these function or which

particular situation which particular

scenario inside the electric vehicle

should use which type of sensor this

question needs to be answered. So we

will go step by step of one which we

will be first taking up is the potential

divider based potential divider based

voltage measurements. So there typically

you see couple of resistors which uh uh

Yes, coming back here. So the high

voltage is uh splitted up into uh two

equal halves or perhaps uh two different

uh uh parts if required three different

parts if it is a very high voltage and

the lowest voltage is used to provide

input for the so-called analog to

digital converters.

Then uh uh the next aspect of it uh let

us assume these kinds of uh two resistor

based potential divider circuit. So you

have resistor R1 and you have resistor

R2. So naturally depending upon the

resistance R1 R2 and the amount of

current flowing through it that is based

upon the ohms law the voltage drop

created across these resistors will

vary. So when these resistors are

designed properly,

high voltage is uh a very high voltage

drop occurs across R1 and a small

voltage appears across R2 resistor. Now

this small voltage this small voltage

drop which is occurring across R2 is a

one which is taken and fed to the analog

to digital converter. the analog to

digital converters which are going to

take a decision upon what is the cell

voltage and take appropriate control

decisions. So careful selection of R1 R2

values are supposed to be done and as

usual the potential divider formula

whatever we have come across in our uh

fundamentals. So those things can be

made use of it. For instance, if at all

you're looking at uh the output wtage

which is mentioned as V not, I'll try to

write it. I'm not sure whether it'll be

clear. So this V ratio can be found out

from R1 R2 ratio along with V_UB_1. So

when you are trying to find out V always

what do you do? You just try to write

something like this. So across Vin you

have R1 + R2 resistance and across V out

you have R2. So rearrange these terms in

such a way that we get an expression for

V out. So here we know what V in is

going to be or what the V out

requirement is going to be. So just by

selecting one of these values, the other

value of R2 can be selected and the

voltage can be fed safely to the analog

to digital converters. So this voltage

is used to feed it to the analog to

digital converters and thereby reading

the digital data we make a decision

about what is the input voltage. This is

the simplest method which is frequently

used wherever. Uh there are little

So coming to the next method. So

whatever we are going to see in the next

category type is a capacitive voltage sensor.

sensor.

Yeah couple of questions are there. uh

how hall effect sensor exactly works. It

works based upon hall effect. So these

hall elements as I told you earlier they

are having a special effect when they

are put inside magnetic field kept

inside a magnetic field and when a

current is passing through this hall

effect a voltage called as hall wtage a

potential will be developed across the

perpendicular ends of these hall

sensors. Now by reading this particular

hall wtage we will be able to come to a

conclusion about the amount of current

where they are using these sensors.

Anywhere where we want to measure the

voltage for instance inside a EV if at

all you want to measure the cell voltage

or the DC bus wtage or the traction

inverter wtage everywhere where the

information about the voltage is

required the operating wtage is required

the current wtage is required we need to

employ one of the voltage sensors. So

that is where we come across these

different types and these different

types after we finish discussing about

it briefly um in overview of these

things briefly we will have an idea

about which particular area inside the

EV architecture requires which type of sensor.

Yes, of course EV voltage will not be in

the range of kilov volts but you can

expect something which is greater. For

instance, if you go to the DC bus wtage,

the current architecture goes up to 400

volts. The DC bus wtage, the DC bus

which is going to be serving as a input

for the inverter, that will be 400

volts. Why 400 volts? Once again, a good

question. So, these kinds of high

voltages puts less stress on the uh

conductor, the current stress on the

conductor. So, we will have a discussion

about that at the end of the uh session.

So even uh there are designs where this

DC bus wtage is increased to 800 voltage

precisely because they wanted to reduce

the size of the conductor. If you look

at the size of the conductors which are

having carrying hundreds of ampers,

it'll be very thick. So when we want to

save copper and thereby the weight both

cost and weight when we want to save it,

it is better to allow smaller amount of

current flowing through it without

compromising on the power which is

delivered. So that is where these high

voltages comes into picture. So as long

as uh traction inverters are concerned

we will be talking about high voltages

in the order of 400 volts 390 41 400 410

something in that range depending upon

the current uh cell wtage and then we

talk about the 12vt supply which are

feeding the auxilaries including the

infotainment systems. Sometimes it might

be 48 volt bus structure also. So there

are different wtages which are much

beyond the input capacity of our ADC. So

shortly I'll be showing you the data

sheet of the ADC present in our ATmega

microcontroller. So most of these ADCs

they have a limitation that the input

wtage should be varying in the range of

0 to 5 or perhaps depending upon whether

it is a semos IC or not it might be 0 to

3.3 volt which means that the input

wtage the analog wtage provided to the

ADC it should be maximum of 3.3 or 5

volt 0 to 3.3 or 0 to 5 volt for

instance if you want to measure the

voltage on a 12vt bus system. So

naturally this 12 volt is going to be

much higher than the 5 volt input

requirement. The 5 volt is a maximum

voltage which we can give to the ADC. In

that case 12 volt becomes incompatible.

So naturally we need um means for

stepping down this voltage and making it

compatible with the input of our ADC.

That is where these kinds of voltage

sensors comes into picture.

I hope that query was answered. we will

move on to further discussions. Now we

look at capacitive voltage sensors which

are having a similar kind of structure

that of our potential dividers resistive

potential dividers. Here instead of

resistors we observe couple of

capacitors. So these capacitors create

voltage drop just like the resistive

potential dividers and these potential

dividers serve as a means for measuring

the high voltage. Now these kinds of

sensors are primarily for measuring AC

voltage. It cannot be used for DC

measurement DC voltage measurement and

that to these kinds of voltages are

employed only to measure high voltage ACs.

ACs.

So high tension ACs. So naturally you

can figure out that these are supposed

to be present as a part of the onboard

charges. So when there is a onboard

charger where only the cable goes out

and gets plugged into the electrical

outlet the electricity which is coming

out of the outlet which is going into

the charging port of our electric

vehicle it will be easy in nature. It'll

be usually three-phase

this three-phase 440 volts is a high

voltage. So when we want to have uh

information about how much voltage is

available at our power outlets, this is

the kind of sensors which we go to

capacitive voltage based sensors.

type of sensors. The next one is a

commonly seen sensor which is based upon

the potential coils which is based upon

the principle of transformers.

So we have studied I mean we have uh

understood the fundamentals whenever

there is a change in magnetic flux on

the one side there will be a flux

similar flux induced on the opposite

side. So this particular principle is

exploited for a potential transformer

which is used for measuring the voltage

on the high voltage side. So this can

essentially be thought of as step down

transformer. The high voltage is stepped

down into low voltage. If at all the

input voltage is something like 400, we

can step it down as less as possible by

controlling the number of turns on the

secondary. Just exactly the principle of

the transformer what was studied in the

beginning of our engineering days. That

is what the working principle is behind

these kinds of transducers, these kinds

of sensors. And once again, these kinds

of sensors are employed only to measure

the voltage of AC sources. So without a

change in flux in the primary side the

secondary side is not going to produce

any voltage which means that connecting

a DC voltage something like the bus

wtage of the traction inverter is not

going to give us any output there. So

these kinds of sensor are supposed to be

employed only when there is AC. So once

again these are the ones which are meant

for onboard charges. So you will have a

simple potential coil. The potential

coils output will be processed and then

it'll be used to feed the data to the

ADCs inside the embedded controllers.

The embedded controllers algorithm

processes this digital data and decides

what the voltage is and takes

appropriate control action. Now coming

to the other part of this now when we

look at the output of this transformer

the potential transformer that is also

going to be AC in nature. So these kinds

of ACs they are not compatible with our

ADCs. So if you look into the data sheet

of our ADC it specifically says 0 to 5

volts or sometimes it might be just 0 to

3.3 volts maximum. So this voltage is

DC. So we are looking at clearly a

uniolar wtage. What we are going to have

here at the output is going to be a

bipolar wtage. This is another issue to

be tackled. So we can use simplest

methods of converting this inver full

volt uh full wave into a half wave and

just sampling the half of it. There are

plenty of methods. One of the other

method is to shift the level of this

bipolar waveform and then use this to

feed to the ADC like this. Plenty of

methods are available. One of these

methods can be employed to make this

signal this alternating signal which is

having bipolar voltage which is

Yes, exactly. DC it cannot be used for

measuring we cannot measure DC voltages

by using these kinds of potential

transformer-based voltage sensors. It is

only for measuring AC voltage. So that

is why these the usage of these kinds of

potential transformers. They just stop

with the onboard charges. It doesn't

come any further inside the AV architecture.

Now the third one the hall effect based

sensors. So whatever diagram which we

are looking at is a typical diagram we

end up seeing whenever we uh look into

hall effect based sensors. So

essentially you see uh conductor current

carrying conductor which is marked as IP

there. Uh this one this is your current

carrying conductor. So obviously a

current carrying conductor is going to

produce magnetic field around it.

Something like this you will have

magnetic fields around it. So this

magnetic field is picked up by this

circular arrangement this ring

arrangement. So if you observe very

carefully there is a small break in

between this structure ring structure.

Now this place is where the magnetic

field passes through the air gap like

this. When that happens it makes contact

with this the magnetic lines of forces

makes contact with the hall elements.

Now these hall elements

which is present inside this magnetic

field when subjected to a current when a

current is supplied to flow through

these hall sensors a hall wtage is

produced. So measuring that hall wtage

we will be able to have idea about the

current flowing through it. Now you may

be wondering what is the use of

measuring the current when our objective

is to measure the voltage when these

things are enhanced when these hall

effect sensors the fundamental

configuration is enhanced in such a way

as you look in the other diagram you

will be

yes now it is there. So when these kinds

of sensors are added with a auxiliary

coil as you see as a dark patched on the

left side when it is added with the

auxiliary coil and made into a closed

loop then these kinds of hall effect

sensors which are fundamentally current

sensors or magnetic sensors they can be

used for measuring voltages too. Now the

advantage of these hall sensors are that

they are precise. we do have certain

advantages compared to the uh sensors

voltage sensors what we have been

looking in the previous three slides. So

essentially the high voltage which we

need to measure that is connected the

high voltage terminals. So you know

potential is measured across two

terminals that is why you call that as a

potential difference. Voltage is nothing

but potential difference. So you have

two points where these potential

difference is measured. So the place at

which you want to measure these

potential difference the two nodes those

are connected to these two resistors

essentially these two resistors should

be of high resistance so that it doesn't

load the point at which this potential

is being measured. So typically these

resistances will be very very high and

these resistors when connected forms a

closed loop along with the coil. Now

this circulates a current through this

coil arrangement. Now that current

induces a emf and thereby a magnetic

field and these things are used along

with the fundamental configuration what

we have seen here and this is how a

conventional hall effect based sensor is

used for measuring voltages also. Now we

have to keep in mind the normal

conventional hall effect sensors they

have to be modified in this way in order

to measure the voltage and once again

readym made packages are available IC

based packages are available in order to

perform these kinds of voltage

measurements by using these hall effects

and this is one of the application cases

I mean hall effects are one of the

sensors type of sensors which are

typically used inside the electric

vehicles it is typically used to measure

of the DC bus wtage or even the

auxiliary systems voltage. There are

plenty of places where these gets employed.

Now coming to the next type of sensor

we have something called as a opto

isolated voltage sensor. Typically uh optoouplus

optoouplus

what we have studied as optoouplus.

These can be used in a way to measure

the voltage. So technically these are

not that much used uh inside uh not that

generally used inside EVs but still we

will look into that. So if you look into

the circuit arrangement you will be able

to see the terminal marked as V out. So

this is the point at which the potential

need to be measured with respect to the

reference potential. Now this particular

point is connected to this light

emmitting diode of course through a

current limiting resistor. Now when the

current which is flowing through this

diode emits light, it is picked up by

this optical transistor. Depending upon

the intensity of the light, the bias of

this bipolar junction transistor is

biased and thereby the voltage is

controlled at these output terminals. Of

course, you need to assume that there is

a pull-up resistor here. You will have a

pull-up resistor which is biased with

appropriate voltage. The one which is

compatible with of our that of our ADC.

So this voltage is then converted into

digital. Now this kind of method is also

available but we hardly use it instead

of that since uh this kind of sensors it

gives a advantage primary advantage that

the output side that is this side and

the input side the high voltage side

the high voltage side the input side

they are electrically isolated. See this

one it is electrically isolated. this

particular area. So this particular area

electrically isolates these two

sections, the output section and the

input section. So remember these kinds

of input sections can typically handle

around 400 volts a high voltage whereas

on the other hand the ADC which is

present inside your embedded controller

typically a microcontroller small

microcontroller it just handle voltage

around 5 voltage or 3.3 volts. So if any

fault happens on this side that fault

shouldn't propagate to the signal side

or most of all it shouldn't create any

kind of hazardous situation for the

operator that is a human being. So in

this context isolation electrical

isolation is required. When isolation is

required the methods like these should

be employed and this is where the

isolation amplifierbased voltage sensors

comes into picture.

So these are primarily used in the IC

based solutions. These are primarily

used in electric vehicle architecture.

So this diagram whatever you have seen

it is a Texas instrument based solution.

You have if you just uh type in this

part number you will get additional

information about that. Now if you look

into the diagram you will be able to see

the high voltage side this side on the

left side and the low voltage side the

place where the information is supposed

to be taken and fed to the embedded

controller on the right side. Now in

between these two you have circuit

elements which makes the signal

compatible, provides electrical

isolation and of course conditions the

signal and then provides it to the

controller ADC part input of the digital

device. So all these functions are done

by this isolation amplifier based

voltage sensors. And by the way if you

look into it you will be seeing three

sensors. Just a minute let me erase everything.

Yes. So if you look at the input side,

you see three resistors here. So in the

earlier diagram whatever we have seen to

understand the concept of potential

divider based voltage sensor, we just

saw two voltage dividers. So in this

case we are seeing three. So these are

kind of uh extra protective features. So

normally these two resistors R1 and R2

it will be in the order of mega ohms.

it'll be in the order of megga ohms. On

the other hand, these things might be in

the order of kiloohms. The one what you

see at here. So this one may typically

be around kiloohms. So these

combinations ensures that the voltage is

safe enough to be handled by this

isolation amplifier. So we always taken

these kinds of extra protective

measures. We make sure this voltage is

absolutely safe for handling. Safe for

Yeah, let me just look into the chat

Okay. Why is it biased? I couldn't

understand the question. I think you are

referring to the optical isolators

based uh voltage sensors. Uh it is like

a conventional bipolar junction

transistor. So these bipolar junction

transistors BJTs conventionally we have

seen there will be a base terminal which

will be biased by a current. BJTs are

naturally current control devices. So

they are controlled by the amount of

current flowing into the base junction

base terminal. So naturally these are

current control devices. So when a

current is provided to the base it gets

biased that is a conventional

transistors. Whereas optical transistor

this bias is provised by light rays. It

is optical transistor. So naturally the

bias whatever electrical signal which

was biasing the transistors that has

been replaced by the light rays. So

depending upon the intensity of the

light rays the base will be biased. I

think that is what you are referring to.

We can use clampers for shifting.

Clampers for shifting. Uh if you could

be more specific on the question we can

So clampers I mean the way of uh

signal isolation. So those kinds of

signal isolation things I presume that

is what you are referring to. You will

have a kind of clip arrangement. So

these clip arrangements are flexible to

be opened at one end and it'll be

clamped around a conductor in order to

measure the current. I presume that's

what you are referring to. These kinds

of clampers are especially used for

measuring currents. It is essentially a

uh current transformer. What you have

the kind of arrangement what you have

inside the clampers. It is something

like a current transformer.

Okay. So once we have finished

discussion of voltage sensors, we will

be of course looking into the current

transformers. At that time maybe we can

elaborately discuss about these clamper

Okay. I think you are referring to opamp

based uh level shifting. That's what you

are trying to say. Clampers with respect

to opamps. Yeah, of course you can do

that. when it comes to shifting the

levels of the AC signal at the output of

the uh uh step down transformer

potential transformer of course you can

employ these things any any method as

long as we are able to make the signal

compatible for the ADC those things can

be employed anything okay now coming

back to the isolation amplifier based

voltage sensors so these are customuilt

solutions especially tuned for reliable

operation ations like in EVs. So these

are custom IC based solutions. So that

is why you will be seeing employment of

these kinds of isolation amplifier based

voltage sensors commonly used there.

And another thing is the dedicated IC A6

application specific integrated circuits

which sits as a part of the battery

management system itself. So you have

dedicated IC's which perform only the

function of monitoring the cell voltage

and other parameters and take a decision

of these things. So these are custom

IC's. So these are application specific

IC's. Once again just like the previous

amplifier based solutions these are

available in the form of IC packages

which can be readily employed into our

Now we will just have a kind of uh uh

discussion. So there are different uh

voltages which are supposed to be

measured inside a EV. For instance, as

we were uh talking earlier, we may be

required to measure each and every

cell's voltage. We may be required to

measure the packs voltage. We might be

required to measure the DC bus wtage

like that. So we will try to figure out

which among the voltage sensing methods

we have seen can be employed for

measuring the voltages listed here. For

instance, if at all our objective is to

measure the cell wtage. We have to

remember the cell which we are referring

to is the lithium ion cell. So the

lithium ion cell typically the voltage

is 3.7 nominal voltage whereas it can

vary to a maximum of 4.1 volt. Sometimes

it may go to 4.2 that depends upon the

manufacturer but we will keep 4.1 and it

might be allowed to discharge up to 3.1

volts or 3.6 depending upon once again

the battery pack manufacturer. So we

will assume this particular range of 3.1

to 4.1. So if this is our range of

voltage which need to be measured by the

voltage sensor 3.1 to 4.1. So which

among these sensors typically we can

think of if you can chat then

you can put your answer in the chat or

else I'll uh say the answer after some

time. So if it is a voltage of in the

range of 3.1 to 4.1 that needs to be measured

measured

then which among the available options

we see the available options here

starting from

resistive voltage divider then

capacitive voltage divider transformer

based voltage sensors hall effects

isolation amplifier based then specific

Can you suggest any one of these

available options for measuring the cell voltage?

voltage?

Naturally, capacitive voltage sensor is

ruled out because it is meant for

measuring only AC.

We can rule out this potential coil,

potential transformer based solution

also. The rest of the options all are

available for employment. Isolation

amplifier based voltage sensor that is a

very good choice. This can be used

and even the hall effect based sensor

can be employed. Even the resistor

voltage divider they can be employed.

But since there are vendors which

provide IC based monitoring solutions.

Most of the times inside the BMS they

employ these dedicated chips which are

meant for monitoring the cells. So these

are referred usually as cell monitors,

CMS. In your architectural diagram or in

your block diagram, whenever you look

into the block diagram of EVs, you might

end up seeing these kinds of

abbreviations. They refer to cell

monitors. So these kinds of cell

monitors, they are performed by these

dedicated IC's. So we can use either one

of these solutions starting from the

resistive voltage divider or a halo

effect based sensor isolation amplifier

voltage monitoring IC dedicated voltage

monitoring IC

all of these are wise choices. Now

coming to the next question now we have

suggested some kind of voltage sensing

option for this cell voltage

measurement. On what basis do we decide

whether to use a resistive voltage

divider or a hall effect based sensor or

even the BMS voltage monitoring IC. Now

this is a question which we need to have

understanding about thoroughly.

It is supposed to be a very safety

critical place where this voltage

measurement has to happen or the voltage

measurement sensor is supposed to be

operating in a safety critical

environment. Now this is where the

standards comes into picture. So

yesterday in our uh discussions we were

talking about the ISO standard 26262

which talks about the safety aspects. So

one aspect of this is ASIL levels. So

what you call it as S I L. So maybe I'll

write it here. So these are

the levels of safety which we are

supposed to look into while we are

making design decisions. So this ASEL

stands for you can Google it and uh try

to get more information on that. It is

automative safety integrity level.

automative safety integrity level. So

essentially these as a as levels they

talk about or they are involved about

safety aspects. So safety aspects are

critical. Now when we come to these S

levels we have different levels starting

from A to D. D being the highest and A

being the lowest. This is the highest uh

uh level of safety integrity that is

needed. So depending upon the ASI level

that is that we are aiming for we have

to go for one of these solutions. If at

all we are looking at A or B level then

resistive voltage based solutions might

be more than sufficient. On the other

hand, if you are looking at D level as D

levels, then definitely we have to go

for a reliable solution, not even hall

sensors. We may either be using

isolation amplifier based or a dedicated

voltage monitoring IC safe at all. The

safety aspect is in SLD level. So these

kinds of standards do

uh dominate the decision making process

in the design. So that is another thing

which we have to keep in mind while we

are picking up appropriate sensors and

while we are developing solutions for

your EVs not just EVs any place where

Okay. Now we will continue our

discussion about the selection of a

sensor for the other types of voltage

management. Now a bunch of these kinds

of uh cells lithium cells are made as a

battery pack first as a module something

like this you have a bunch of them

arranged and put inside a module any

number of such modules are made into a

pack. So if at all our requirement is to

measure the voltage across a battery

pack as such

what kind of sensing option can we go

for? Definitely we cannot go for

capacitive voltage sensor because it is

meant for AC measurement transformer

based solutions also for AC voltage

measurement. So we will rule those

things out. Once again we have one 2 3

and four solutions in our disposal. We

Battery pack wtage measurement. What

kind of voltage sensing method we can go for?

If you can put up your answer in the

chat box, we can have a discussion on that.

that.

I know now you are thinking the answer

is debatable. Yes, absolutely you're

right. The answer is subject to debate.

It is entirely based upon this SL level.

But still we end up using either hall

effect based voltage sensors or we go

for isolation amplifier based sensors.

We do have ion sensors dedicated IC's

which makes these kinds of voltage

measurements possible for a battery pack wtage.

Now try to figure out what kind of

sensor we can make use of for the

So the traction inverter

is a one which provides the power to the

motor electric motor. So this electric

motor might be like a VLDC motor what

you see in your electric scooters or it

might be a SRM motor switch reluctance

motor or permanent magnet synchronous

motor. Still SRMs have not come into

widely come into EVs. PMS's permanent

magnet synchronous motors we can look

into it. So assuming that your motor is

one of these categories of course you

may think about induction motors too.

Induction motors are used in some of the

heavyduty electric vehicles something

like trucks not widely employed but

those are also being used. Now assuming

that you have these kinds of motors they

need to be driven by an inverter. Now

this inverter requires a DC bus voltage.

Naturally the DC bus voltage will be

around 400 volts.

This 400 volt will be supplying power to

the motor. So when you are trying to

assess what is the bus wtage

not necessarily always this bus wtage

will be constantly held at 400 it might

be different little bit lower a little

bit higher it might be different. So if

at all we want to maintain a constant

voltage on the DC bus then we need to

sense the DC bus wtage which typically

is around 400 volts which is

significantly higher to that of the ADC.

So what kind of methods we can suggest?

Yes, isolation amplifier based sensor,

Typically you can go for hall effect

based sensor also. And once again the

selection of one of these two can be

subjected to darcel safety levels.

And when you see these kinds of

hallbased sensors, they are almost

always they are combined with a

resistive voltage dividers. So a

resistive voltage divider is used to

strip down the voltage something like

this and the low voltage drop created by

the lower resistor that is being used

for the hall sensor. So this is a

typical combination of arrangement you

will see if at all a hall effect based

voltage sensory is being employed to

measure the traction inverters bus

wtage. Of course the output wtage

traction inverters output all wtage also

matters. So if it is AC voltage that you

are looking into once again you have to

look for one of these kinds of sensors

and typically capacitive voltage sensors

they are rolled out you might be end up

selecting transformer-based voltage

sensors. Now coming to the onboard charges

charges

recollect what these onboard charges are

or what is the architecture of these

onboard charges. So these kinds of

onboard charges are the ones which

which uh has all kind of all kind of

converters and uh controllers everything

present inside the electric vehicle

itself. Remember why it is called as

onboard charger because everything is

present on board you call it as onboard

charger. So naturally the outlet what we

have from there the AC supply comes all

the way to the inlet of our electric

vehicle. So which means that you are

dealing with the AC supply at our

electric inlet. So you need to have idea

about what wtage is available on these

inlet ports the car inlet ports. So in

that context you will be end up

selecting either one of these solutions

capacitive voltage trans sensors or

potential transformer based transformer

Yes you have you can go for a

combination also. Yeah that's right. You

can go for a combination too.

And finally for the auxiliary systems,

the auxiliary systems can be lighting

lighting

it can be related to the horn systems,

operation of the window screens, the

signal lights, tail lights or it can be

related to the uh sensors what you have

to detect the obstacles

or infotainment. All of these things

here the safety criticality is not there

that serious which means that we can

come to come down to levels of A or

perhaps B even B is not required we can

go to uh low safety or even no SL levels

also is okay which means that here the

usage of a sensor can be as simple as

that of our resistive dividers. So this

will be simple and also it will be

cheap. So these kinds of sensors

resistive voltage divider based sensors

they can obviously be chosen for

measuring the voltage for which is going

to the auxiliary systems. Usually this

will be 12vt systems or sometimes it

will be little more also. Yes, windows

wipers all these things we can go for

these kinds of uh resistive voltage

divider based sensors. Now there is one

point which we have to remember while we

are selecting these kinds of uh

potential divider based voltage sensing

methods. So even though these are used

widely for because of their simplicity

and for uh uh their advantage of uh cost

effectiveness they do come with certain

disadvantages. So if at all we end up

using the normal resistors which we

commonly come across in our

undergraduate labs. So which are made of

wire wound resistors. So these are prone

to value change over a period of time.

Not only that these kinds of resistors

are they are very prone to temperatures.

You would have heard about positive

temperature coefficient that is the

temperature affecting the resistivity of

the resistor. So when we have these

kinds of issues and when measurement of

the voltage becomes a little bit

critical it is always advisable to avoid

using these kinds of resistors the

normal resistors you can go for

dedicatedly manufactured automotive

grade resistors when we are building

these potential divider based voltage

sensing methods it is always better to

select our components carefully select

our resistors carefully or if at all it

is possible we can go for one of the

other methods too. One of the other

Okay, we will move on. Hope uh this

particular part about voltage sensor is

uh uh we have reviewed it.

uh we will come to uh incorporating

these voltage measurements for uh uh

incorporating protection aspects or

maybe control aspects. So in this

session we will be just discussing about

the protection aspects

how to protect our cell during the

charge conditions. So while the lithium

battery cell is lithium cell is being

charged you know that it is not supposed

to be uh allowed to go beyond a voltage

of 4.1 because of various reasons. So

naturally when the cell voltage reaches

four or 4.1 or in some cases 4.2 in some

manufacturer's case you will be

interested you will be uh uh more

oriented to cut off this voltage. That

is where this over voltage protection

comes into picture. Now we have the

information about the cell voltage from

our voltage sensor. You have your

voltage sensor. So this particular

voltage sensor is given to the embedded

controller. So which has inbuilt ADC.

The analog signal is given. The digital

signal is obtained and this digital

signal is processed and the decision

need to be taken. Now the decision which

is going to be taken is going to be

whether to disconnect the cell from the

charger or not. Assume you have a

charger which is charging our

battery cell. So you have a cell like

this a single cell. We will just keep

for simplicity sake we will just assume

one single cell. So now this cell

assuming that it is connected to a

charger and it is getting charged. We

have to monitor the cell voltage continuously

continuously

using the cell monitors. And whenever

the voltage reaches 4.1 volt, assume

your objective is to cut off this

charging your objective is to isolate

this cell from the charger. When this

isolation is supposed to be happening

when you are having a cell voltage of

4.1. So we will be installing a

protective mechanism which isolates this

cell from the charge. Typically it can

be something like a switch not ordinary

uh switch what we use to control our

lights and fans. So these switches will

be semiconductor switches typically a

power masset.

So these kinds of semiconductor switches

are employed in order to isolate the

cell battery cell from the charger. So

this is done by issuing a control signal

to this semiconductor switch. It is

something like a BJT. You can visualize

this switch as something like a BJT.

Only thing it will be voltage controlled

switch. So this control terminal the

control terminal which controls whether

the switch needs to remain closed or

open that comes from your embedded

controller. Now the question is how will

your embedded controller know when to

keep the switch closed or when to

open the switch. So this entirely should

happen based upon a feedback. The

feedback information which is coming

from the cell using a voltage sensing

method a voltage sensor we measure the

voltage we provide it to the ADC.

So these ADCs in all these embedded

controllers will be inbuilt. When these

ADCs converts the signal, a set of

digital data, zeros and ones, a group of

zeros and ones are generated in order to

indicate what the cell wtage is. That

particular information is processed and

a decision is taken whether to open the

switch or closed. Now starting from 3.1

volts, assume the voltage is gradually

rising 3.2 3.5 3.7 8 4.1.

The moment the voltage reaches 4.1 the

lithium ion cells voltage reaches 4.1

the voltage sensor gives the information

to the controller based upon the control

algorithm what you have written the

emboded systems programming what you

have done based upon that programming

this controller takes the decision to

open the switch so it issues the control

signal at this juncture to open the

switch and thereby safeguard your cell

from over voltage so this is typically

what is supposed to be done. So in order

to do this functionality to in order to

implement this functionality,

what are the things we need? We need a

sensing device which collects the data.

Just recollect the flow what we have

seen in the previous session. The flow

starting from data collection all the

way to communication. So the first step

is to collect the data. Then process the

data. Of course here there is a

conversion stage. process the data and

then take a decision to control it.

Collect, process and then control. So in

order to collect this we have used a

voltage sensor. So in order to make this

compatible with the digital device now

we need the help of a converter a

converter which converts a analog signal

to a digital signal and this is where

the analog to digital converters comes

into picture. So these are essentially

uh type converters a converters which

converts electrical signal in one type

one form to another analog form to

digital form. Now when we talk about

these kinds of ADCs always the number of

bits to which this analog signal is

getting converted to that is one of the

important parameters we have to look

into ADC. So we will talk about this

little bit in detail because a selection

of embedded controller a selection of a

microcontroller with a required ADC is

very important for implementing these

kinds of protective features or control

aspects very thoroughly in a very

reliable way. So in that context a basic

understanding about these analog to

digital converters are very much

required. Now assume you have a signal

which is varying something like this. We

will take uh a signal like this or a

simple signal a DC signal itself.

Since we are measuring DC voltage we

will talk about DC itself.

So assume we have some sort of signal

like this.

5 volts need to be measured. Now in

order to mesh represent this number five

in digital we will require some number

of bits. We may have n number of bits.

So we need to see what is the maximum

number of bits. So now we need to have a

recollection of the digital concepts

what has been acquired in the basic

classes including our PUC's. Now binary

representation of numbers is what we are

looking into. So in order to represent

number five, how many maximum bits are

required? That is the question which we

have to find answered.

Now what will be the number of bits to

represent this number five? If you have

one bit, you can represent two numbers.

If you have two bits, you can represent

four numbers like that. In order to

represent five, you will require yes

absolutely three bits. It is one not

one. So we will require three bits

minimum to represent this information

five. So in our case the voltage is

going to go from 0 to 4.1. So if it is 0

to 5 if it is either zero or one or two

or three or these things whole numbers

then very easily we can be satisfied

with these three bits. Now the problem

is we need to detect the voltage to the

precision of.1 volt which means that the

current three bit representation is not

sufficient. This is when the number of

output bits produced by the ADC becomes

significant. That becomes one of the

important feature. So using three bits

we can measure represent only numbers

starting from 0 to 8. That's the

maximum. But we have a requirement to

represent additional information. So

what we do? We select more number of

bits. For instance, we select four bits.

We will say we have selected B, B1, B2

and B3.

So using these three bits, we will be

able to represent the whole number from

0 to 8. Then this particular extra bit

which can either have zero or one

information can be used for representing the

the

fractional part.

It can be used for representing the

fractional part. Now whatever fractional

part which we are trying to represent

with this one bit will be very small

only two states only two numbers are

available which means that we can either

configure to represent this as zero or

one that's all either 0 five or one you

can keep it that way also 0.5 or one so

in this case the precision suffers so

now what we do we want to represent this

decimal information, this fractional

information to a very accurate manner

which means that we have to extend the

number of bits allotted for representing

this fractional information also. So now

you see where we are going

representation of this analog signal in

the form of binary signal needs to be

done by considering the accuracy of the

analog signal which we want to represent it with. So that is where the different

it with. So that is where the different uh ADCs comes into picture.

uh ADCs comes into picture. So we have simple 4bit ADCs, we have 8

So we have simple 4bit ADCs, we have 8 bit ADCs, we have 10 bit ADCs, we do

bit ADCs, we have 10 bit ADCs, we do have 16 bit ADCs. So when we naturally

have 16 bit ADCs. So when we naturally go for higher number of bits on the

go for higher number of bits on the digital side, the output side the

digital side, the output side the accuracy with which we can read the

accuracy with which we can read the input wtage will increase. Whereas when

input wtage will increase. Whereas when we select a ADC which is having lesser

we select a ADC which is having lesser number of digital outputs naturally the

number of digital outputs naturally the accuracy will suffer. Now it is once

accuracy will suffer. Now it is once again the embedded systems engineer's

again the embedded systems engineer's job who is into the design aspects. It

job who is into the design aspects. It is his job to decide what accuracy is

is his job to decide what accuracy is needed. What is a range of parameters he

needed. What is a range of parameters he want to represent or measure? What is

want to represent or measure? What is accuracy with which we want to measure?

accuracy with which we want to measure? Then take a decision on the kind of uh

Then take a decision on the kind of uh the kind of uh ADC which we want to

the kind of uh ADC which we want to select. Now with this uh note we will

select. Now with this uh note we will proceed further or else it'll become too

proceed further or else it'll become too theoretical.

Yes. A small recollection of the over voltage protection mechanisms.

voltage protection mechanisms. So we are talking about over voltage

So we are talking about over voltage protection implementation by using

protection implementation by using embedded controllers. So we have

embedded controllers. So we have understood that uh voltage sensor is

understood that uh voltage sensor is essential. The voltage sensor senses the

essential. The voltage sensor senses the voltage gives an output. This analog

voltage gives an output. This analog output need to be sampled that is

output need to be sampled that is converted into a digital. This digital

converted into a digital. This digital information need to be processed. So a

information need to be processed. So a computing device is required something

computing device is required something like a microcontroller. Then once this

like a microcontroller. Then once this decision is made, this decision should

decision is made, this decision should be used for actuating the outputs. So in

be used for actuating the outputs. So in this case isolating the battery cell

this case isolating the battery cell from the charger. So how this mechanism

from the charger. So how this mechanism can be implemented? what are the

can be implemented? what are the components which are key in uh

components which are key in uh implementing this over voltage

implementing this over voltage protection that is what we are looking

protection that is what we are looking into. So obviously for isolating you

into. So obviously for isolating you need a switching mechanism that is where

need a switching mechanism that is where your semiconductor switches like MOSFETs

your semiconductor switches like MOSFETs comes into pictures. So these are

comes into pictures. So these are essentially for either connecting or

essentially for either connecting or disconnecting the cell to the charger.

disconnecting the cell to the charger. These are meant for either connecting

These are meant for either connecting the battery cell or disconnecting the

the battery cell or disconnecting the battery cell from the charger. So

battery cell from the charger. So obviously apart from this there are

obviously apart from this there are other things that should be present

other things that should be present considering safety aspects. So if it is

considering safety aspects. So if it is simple implementation of the

simple implementation of the disconnection logic mass is more than

disconnection logic mass is more than sufficient. But we are talking about

sufficient. But we are talking about automoils where safety is one of the

automoils where safety is one of the critical aspect the asel standards as

critical aspect the asel standards as levels what we are talking about in the

levels what we are talking about in the ISO standard you have to recollect those

ISO standard you have to recollect those things. So if at all the safety level

things. So if at all the safety level with which you have to implement these

with which you have to implement these things are critical. If it is anywhere

things are critical. If it is anywhere near B or C even if it is B then you

near B or C even if it is B then you have to think about adding redundant

have to think about adding redundant mechanisms and failsafe mechanisms. So

mechanisms and failsafe mechanisms. So some of those aspects are what we see

some of those aspects are what we see there something called as TVS diodes and

there something called as TVS diodes and you do have the regular fuses also

you do have the regular fuses also available as a part of these over

available as a part of these over voltage protection mechanisms. Now when

voltage protection mechanisms. Now when the cell is getting charged normally

the cell is getting charged normally under steady state the so-called steady

under steady state the so-called steady state when you are looking at the steady

state when you are looking at the steady state condition the voltage will be

state condition the voltage will be fairly constant. So in the previous two

fairly constant. So in the previous two weeks when you have been discussing

weeks when you have been discussing about the battery uh related aspects you

about the battery uh related aspects you would have studied about the different

would have studied about the different kinds of charging methods constant

kinds of charging methods constant voltage charging constant current

voltage charging constant current variable voltage or variable current. So

variable voltage or variable current. So in all of these aspects the voltage is

in all of these aspects the voltage is either kept fixed or it'll be changing

either kept fixed or it'll be changing very slowly. So as long as the charging

very slowly. So as long as the charging voltage is slowly varying we don't have

voltage is slowly varying we don't have any more requirement apart from the

any more requirement apart from the masset but normally uh not always this

masset but normally uh not always this uh will be the condition. Sometimes

uh will be the condition. Sometimes there will be transients there will be a

there will be transients there will be a sudden surge in the power coming to the

sudden surge in the power coming to the battery cell. So if such a kind of surge

battery cell. So if such a kind of surge arises because of any fault or because

arises because of any fault or because of any malfunction on the charger side

of any malfunction on the charger side then how to protect our cell you know

then how to protect our cell you know that lithium cells are very temperature

that lithium cells are very temperature sensitive. So these kinds of aspects

sensitive. So these kinds of aspects makes us to look into the safety aspects

makes us to look into the safety aspects also. So that is where the transient

also. So that is where the transient suppressing diodes transient voltage

suppressing diodes transient voltage suppressing diodes comes into picture.

suppressing diodes comes into picture. So these are essentially put somewhere

So these are essentially put somewhere like uh where is my mouse?

Yes. So you essentially have these kinds of uh uh uh diodes put up somewhere in

of uh uh uh diodes put up somewhere in parallel like this. The TVS diodes goes

parallel like this. The TVS diodes goes in parallel with the cell something like

in parallel with the cell something like so. This is your charger. So from here

so. This is your charger. So from here the charge is being transported to your

the charge is being transported to your cell. So this

cell. So this action will be happening along with the

action will be happening along with the disconnecting or connecting switch. Now

disconnecting or connecting switch. Now when the transient occurs this TVs diode

when the transient occurs this TVs diode acts as a safety wall. Whatever excess

acts as a safety wall. Whatever excess uh voltage that surge that has happened

uh voltage that surge that has happened that will be passing through this TVS

that will be passing through this TVS diode the suppressing transient voltage

diode the suppressing transient voltage suppressing diode and thereby this

suppressing diode and thereby this battery cell will be safeguarded. So

battery cell will be safeguarded. So these are safety mechanism which usually

these are safety mechanism which usually you will be seeing with BMS uh I mean

you will be seeing with BMS uh I mean battery cell control mechanisms

battery cell control mechanisms and naturally the last line of defense

and naturally the last line of defense is your fuse. The regular fuse what we

is your fuse. The regular fuse what we see in our homes such a kind of fuse

see in our homes such a kind of fuse whenever there is a current which is

whenever there is a current which is flowing beyond a permitted level

flowing beyond a permitted level obviously it fuses it melts thereby

obviously it fuses it melts thereby isolating both sides of the circuit the

isolating both sides of the circuit the load side and the uh source side.

load side and the uh source side. So until now do you have any questions?

TVS diodes. I think just now we discussed about TVS diodes.

discussed about TVS diodes. Yes. So these are the three components

Yes. So these are the three components of the over voltage protection

of the over voltage protection mechanisms which conventionally go into

mechanisms which conventionally go into every single battery over voltage

every single battery over voltage protection of EV battery packs.

protection of EV battery packs. Now coming to the crux of it. This uh

Now coming to the crux of it. This uh entire week session is supposed to be

entire week session is supposed to be about embedded controllers. How we can

about embedded controllers. How we can realize the requirements by using

realize the requirements by using embedded controllers. So that is why we

embedded controllers. So that is why we have been looking into uh things which

have been looking into uh things which are required to build embedded

are required to build embedded controllers. We have been looking into

controllers. We have been looking into for the past two sessions. Now we will

for the past two sessions. Now we will spend a little bit of time on discussing

spend a little bit of time on discussing about the different so-called

about the different so-called peripherals which we need from a

peripherals which we need from a microcontroller. So microcontrollers are

microcontroller. So microcontrollers are the embedded control device.

the embedded control device. So in those things what kind of

So in those things what kind of peripheral functions are preferable for

peripheral functions are preferable for automative stages for automative

automative stages for automative applications. So typically we can come

applications. So typically we can come across the things which are listed in

across the things which are listed in the first point. Analog to digital

the first point. Analog to digital converters, interrupt mechanisms, timer

converters, interrupt mechanisms, timer counter mechanisms. So these three

counter mechanisms. So these three things will be common for almost every

things will be common for almost every microcontroller which you see in the

microcontroller which you see in the market. Whether it is for automotive or

market. Whether it is for automotive or whether it is for industrial drives or

whether it is for industrial drives or any applications even for uh any any

any applications even for uh any any systems wherever you see these kinds of

systems wherever you see these kinds of uh peripherals will be by default

uh peripherals will be by default present in the microcontrollers. Apart

present in the microcontrollers. Apart from that depending upon the category of

from that depending upon the category of applications where these

applications where these microcontrollers are meant to be used in

microcontrollers are meant to be used in we might see something called as PWM

we might see something called as PWM controller modules, capture modules,

controller modules, capture modules, something called as QEP modules, quadrer

something called as QEP modules, quadrer encoder pulse modules. There are variety

encoder pulse modules. There are variety of these kinds of peripheral functions

of these kinds of peripheral functions added on to the microcontroller core. So

added on to the microcontroller core. So depending upon the application what

depending upon the application what you're dealing with it is the embedded

you're dealing with it is the embedded system design engineer's duty to select

system design engineer's duty to select a proper microcontroller with the

a proper microcontroller with the peripherals with the required

peripherals with the required peripherals. So sometimes you might be

peripherals. So sometimes you might be required to communicate information

required to communicate information frequently. For instance the

frequently. For instance the infotainment systems or the status

infotainment systems or the status systems agar systems all these things

systems agar systems all these things information will be passing on front and

information will be passing on front and back of the vehicle. So these kinds of

back of the vehicle. So these kinds of places communication will be the core

places communication will be the core job performed by the embedded

job performed by the embedded controllers. In those places peripheral

controllers. In those places peripheral functions these peripheral functions

functions these peripheral functions should be a part of the embedded

should be a part of the embedded controller. So primarily we are looking

controller. So primarily we are looking into ADCs, interrupts and timer

into ADCs, interrupts and timer counters.

So you can have additional things also whatever which is not mentioned here

whatever which is not mentioned here those things also you can see as a part

those things also you can see as a part of it. So we just have to scroll through

of it. So we just have to scroll through the manufacturer's website and then

the manufacturer's website and then shortlist the microcontroller which is

shortlist the microcontroller which is required for your embedded

required for your embedded implementation.

implementation. So we have been talking about uh ADCs

So we have been talking about uh ADCs for a while. We have illustration of

for a while. We have illustration of that the analog signal is usually

that the analog signal is usually represented in the form of digital

represented in the form of digital information. The number of bits with

information. The number of bits with which the output need to be represented

which the output need to be represented that always is important to be taken

that always is important to be taken care of. More number of bits more better

care of. More number of bits more better is your measurement accuracy.

is your measurement accuracy. Okay, now we are looking into the data

Okay, now we are looking into the data sheet. Okay, do you need a break? It's

sheet. Okay, do you need a break? It's 11:30. Maybe another 5 10 minutes we can

11:30. Maybe another 5 10 minutes we can wind up the session and we can continue

wind up the session and we can continue in the afternoon session. I hope it is

in the afternoon session. I hope it is okay. Maybe by 11:35

okay. Maybe by 11:35 40 we will uh wind up the session and

40 we will uh wind up the session and afternoon we will continue this. So

afternoon we will continue this. So afternoon we will be taking simple uh

afternoon we will be taking simple uh circuit not the sophisticated level of

circuit not the sophisticated level of automative electronics we will take

automative electronics we will take simple circuits just like uh uh this

simple circuits just like uh uh this over voltage protection then we will try

over voltage protection then we will try to implement that and uh uh we will see

to implement that and uh uh we will see those things a little bit of uh head

those things a little bit of uh head start for whatever you might end up

start for whatever you might end up doing as a uh EV engineer.

doing as a uh EV engineer. Okay. So whenever we are making a choice

Okay. So whenever we are making a choice of the ADCs we have to look into certain

of the ADCs we have to look into certain parameters. The first and foremost thing

parameters. The first and foremost thing is the resolution.

is the resolution. How many number of bits digital bits are

How many number of bits digital bits are used to represent the input analog

used to represent the input analog signal that decides the resolution of

signal that decides the resolution of your ADC. The more number here, the

your ADC. The more number here, the higher number you have here, better

higher number you have here, better resolution you'll be getting it. So you

resolution you'll be getting it. So you have to make a judicious choice uh

have to make a judicious choice uh trade-off we can say between the higher

trade-off we can say between the higher number of uh uh output bit resolution

number of uh uh output bit resolution and the conversion speed and processing

and the conversion speed and processing efficiency. We may have to make a

efficiency. We may have to make a trade-off. Typically uh 12 bit or 16 bit

trade-off. Typically uh 12 bit or 16 bit ADC is more than sufficient for your

ADC is more than sufficient for your battery packs. 12 bit 16 bits more than

battery packs. 12 bit 16 bits more than sufficient. It should be more than

sufficient. It should be more than sufficient. So whatever microcontroller

sufficient. So whatever microcontroller you have been using your favorite Uno

you have been using your favorite Uno boards that employ this microcontroller.

boards that employ this microcontroller. By the way those kinds of boards ADNA

By the way those kinds of boards ADNA boards may not be used in automotive

boards may not be used in automotive industry but definitely these kinds of

industry but definitely these kinds of microcontrollers the microcontrollers

microcontrollers the microcontrollers present on those boards. You may see

present on those boards. You may see these applications there may not be in

these applications there may not be in the form of a board- based solutions

the form of a board- based solutions like that dedicated custom based

like that dedicated custom based solutions. You will see these kinds of

solutions. You will see these kinds of microcontrollers. So we have picked up

microcontrollers. So we have picked up this just for the sake of uh

this just for the sake of uh understanding certain issues. Now if we

understanding certain issues. Now if we look into the data sheet of your

look into the data sheet of your microcontroller you will be seeing these

microcontroller you will be seeing these datas. For instance the resolution one

datas. For instance the resolution one of the important parameter which you

of the important parameter which you have to look into. Then the conversion

have to look into. Then the conversion time this decides with what speed the

time this decides with what speed the data is going to get converted and with

data is going to get converted and with what speed we can process this data to

what speed we can process this data to take the control decision. Then

take the control decision. Then naturally how many signals can

naturally how many signals can simultaneously be processed or how many

simultaneously be processed or how many number of signals can be maximum sampled

number of signals can be maximum sampled by using this ADC and of course the

by using this ADC and of course the range of voltage which can be covered by

range of voltage which can be covered by our ADC. So these are some of the

our ADC. So these are some of the important parameters. For instance, if

important parameters. For instance, if we talk about this ATMA 328

we talk about this ATMA 328 microcontroller, the range of voltage

microcontroller, the range of voltage what we can measure using this ADC is

what we can measure using this ADC is ranging from zero to VCC. So if you are

ranging from zero to VCC. So if you are connecting your VCC to 5 volts, so the

connecting your VCC to 5 volts, so the range will be 0 to 5 volts. So if at all

range will be 0 to 5 volts. So if at all you are trying to measure the battery

you are trying to measure the battery pack wtage which typically may go to a

pack wtage which typically may go to a DC bus voltage which can typically go to

DC bus voltage which can typically go to 400 volts. This 400 volts should be

400 volts. This 400 volts should be stepped down and made compatible to this

stepped down and made compatible to this range. 0 to 400 range should be made

range. 0 to 400 range should be made compatible with 0 to 5 volt range. Which

compatible with 0 to 5 volt range. Which means that when the maximum voltage

means that when the maximum voltage which should be measured is present the

which should be measured is present the conversion circuit whatever we are using

conversion circuit whatever we are using the the interfacing circuit that should

the the interfacing circuit that should produce a maximum wtage of five at the

produce a maximum wtage of five at the output side. So this is the job of your

output side. So this is the job of your signal conditioning networks the

signal conditioning networks the interfacing networks. So in order to

interfacing networks. So in order to have understanding about the

have understanding about the specifications of your interfacing

specifications of your interfacing circuits, you need the information about

circuits, you need the information about the ADC range of input wtages and also

the ADC range of input wtages and also the range of maximum and minimum wtage

the range of maximum and minimum wtage on the input side. The voltage which you

on the input side. The voltage which you are planning to measure. Of course,

are planning to measure. Of course, naturally the other things like the

naturally the other things like the resolution,

resolution, the speed with which the conversion

the speed with which the conversion takes place, all those things do matter.

takes place, all those things do matter. So every single parameter is important.

So every single parameter is important. we are just focusing upon the most

we are just focusing upon the most important parameters.

important parameters. So typically this uh uh 10 bit

So typically this uh uh 10 bit resolution gives us a resolution of two

resolution gives us a resolution of two power 10. So you can have two power 10

power 10. So you can have two power 10 states which means that 1x2 power 10 is

states which means that 1x2 power 10 is a minimum voltage that your ADC can

a minimum voltage that your ADC can sense. So keeping in mind these

sense. So keeping in mind these parameters you can make appropriate

parameters you can make appropriate selection choices.

Now there is a shortcut which uh I can not a shortcut as actually there is a

not a shortcut as actually there is a suggestion which I can give. If you look

suggestion which I can give. If you look into this particular document the data

into this particular document the data sheet uh here itself you can see this is

sheet uh here itself you can see this is page number 2.4. So you have hundreds

page number 2.4. So you have hundreds and hundreds of pages of content which

and hundreds of pages of content which you have to scroll through in order to

you have to scroll through in order to get design choice parameters like this.

get design choice parameters like this. So you need to look into these

So you need to look into these parameters in order to make design

parameters in order to make design choices. So instead of scrolling through

choices. So instead of scrolling through hundreds of hundreds of pages, you can

hundreds of hundreds of pages, you can use your generative agents feed download

use your generative agents feed download the data sheet provided to your uh

the data sheet provided to your uh favorite generative agents and then give

favorite generative agents and then give appropriate query get these kinds of

appropriate query get these kinds of parameters. You just have to give

parameters. You just have to give appropriate prompts to get this

appropriate prompts to get this information. So this is one shortcut

information. So this is one shortcut method which you can employ when you are

method which you can employ when you are going for design jobs. But always it is

going for design jobs. But always it is a best practice to confirm the answers

a best practice to confirm the answers generated by your generative agents.

generated by your generative agents. That is the fail safe method. Once you

That is the fail safe method. Once you have got this information just

have got this information just crossverify once if at all you are using

crossverify once if at all you are using these uh kinds of generative agents.

So we will just have a discussion about the lithium ion cells uh voltage then we

the lithium ion cells uh voltage then we will uh wind up for today.

So the core idea behind implementing the over voltage protection for the lithium

over voltage protection for the lithium ion cell it is multiffolded.

ion cell it is multiffolded. So when you subject your lithium ion

So when you subject your lithium ion cell beyond say the uh common normal

cell beyond say the uh common normal maximum voltage of 4.1 or in some cases

maximum voltage of 4.1 or in some cases 4.2 When your voltage crosses this

4.2 When your voltage crosses this particular threshold limit, then there

particular threshold limit, then there is a chance of your electrolyte uh

is a chance of your electrolyte uh electrode getting broken there will be

electrode getting broken there will be physical uh uh uh uh deformationations

physical uh uh uh uh deformationations inside your battery cell. This is one

inside your battery cell. This is one thing. Not only this, it might lead to

thing. Not only this, it might lead to accelerated aging. Normally if your cell

accelerated aging. Normally if your cell is supposed to sustain for say 600 or

is supposed to sustain for say 600 or 700 cycles it might be subjected to

700 cycles it might be subjected to reduced life cycles. It might just end

reduced life cycles. It might just end up giving 300 or 400 life cycles alone.

up giving 300 or 400 life cycles alone. Not only that during the runtime also

Not only that during the runtime also you will have issues. So when these

you will have issues. So when these cells are subjected to higher wtages

cells are subjected to higher wtages naturally the temperature rise will be

naturally the temperature rise will be there. This essentially might not might

there. This essentially might not might it will affect the internal resistance

it will affect the internal resistance which is going to affect everything on

which is going to affect everything on the cell's performance. It will lead to

the cell's performance. It will lead to reduced capacity. All these issues are

reduced capacity. All these issues are there. So this is the the uh uh core uh

there. So this is the the uh uh core uh issue which we have to tackle and that

issue which we have to tackle and that is why we need to protect our lithium

is why we need to protect our lithium ion cell from over voltage. So you can

ion cell from over voltage. So you can take it a range of voltages depending

take it a range of voltages depending upon what kind of battery chemistry you

upon what kind of battery chemistry you are using and who is supplying these

are using and who is supplying these things. You can have a maximum of 4.4

things. You can have a maximum of 4.4 4.1 volts up to which you can ask this

4.1 volts up to which you can ask this battery charger to charge the cell. You

battery charger to charge the cell. You can set the minimum threshold as 3.4 3.3

can set the minimum threshold as 3.4 3.3 sometimes 3.0 also

and there is additional information we see on the screen. Typically a battery

see on the screen. Typically a battery pack will have thousands of cells.

pack will have thousands of cells. Thousands of cells. Each and every one

Thousands of cells. Each and every one of these cells need to be maintained

of these cells need to be maintained with this particular voltage range. You

with this particular voltage range. You need to protect protect the cell both

need to protect protect the cell both from over voltage and our under voltage.

from over voltage and our under voltage. So both of these has to be done. So any

So both of these has to be done. So any of the voltage sensors clubbed with a

of the voltage sensors clubbed with a proper embedded controller will be doing

proper embedded controller will be doing this particular job.

Now just one last characteristics uh so this might be of uh some interest to you

this might be of uh some interest to you who are actually into BMS developing

who are actually into BMS developing BMS. So if we look into this

BMS. So if we look into this characteristics we will be able to

characteristics we will be able to understand that the uh uh capacity

understand that the uh uh capacity increases when you increase the voltage.

increases when you increase the voltage. See for instance when you have 4.3 volt

See for instance when you have 4.3 volt when the cell is charged to 4.3 volts

when the cell is charged to 4.3 volts the capacity is somewhere around

the capacity is somewhere around 100%age.

100%age. On the other hand the number of cycles

On the other hand the number of cycles charge discharge cycles the number of

charge discharge cycles the number of charge discharge cycles your life cycle

charge discharge cycles your life cycle reduces.

reduces. On the same on the other hand when you

On the same on the other hand when you are constantly charging your battery up

are constantly charging your battery up to a maximum of say 3.9 volts you just

to a maximum of say 3.9 volts you just observe the capacity to which it is

observe the capacity to which it is getting charged is near somewhere around

getting charged is near somewhere around 50%age but at the same time the life

50%age but at the same time the life cycle increases drastically from 1,000

cycle increases drastically from 1,000 all the way to 6,000 six times increases

all the way to 6,000 six times increases there. So naturally you will be required

there. So naturally you will be required to make a tradeoff between these two

to make a tradeoff between these two things. the maximum voltage to which you

things. the maximum voltage to which you allow the cell to charge and the life

allow the cell to charge and the life cycle of the battery. Both of these

cycle of the battery. Both of these things need to be kept in mind before we

things need to be kept in mind before we decide anything upon the control

decide anything upon the control mechanism of your uh charger. So very

mechanism of your uh charger. So very good uh point will be very good thing

good uh point will be very good thing will be to look into the intersection

will be to look into the intersection point of these two things or you can

point of these two things or you can just uh make a judicious tradeoff

just uh make a judicious tradeoff between these two and stop it at 4.1 and

between these two and stop it at 4.1 and after we are going to see how we are

after we are going to see how we are going to we can write a program and put

going to we can write a program and put it on our microcontroller so that a

it on our microcontroller so that a control decision is made when the cell

control decision is made when the cell voltage reaches 4.1 and this is only

voltage reaches 4.1 and this is only like a demo setup. So shortly we will be

like a demo setup. So shortly we will be seeing a demo in the afternoon session

seeing a demo in the afternoon session and we will be discussing something

and we will be discussing something about the current sensors also.

So if you have any queries we can have it or else

it or else we can continue in the afternoon

we can continue in the afternoon session.

Yes, nominal voltage is 3.7 fully charged voltage you can go up to

fully charged voltage you can go up to 4.2

4.2 cutff you can keep it at 3.4 4 3.13 that

cutff you can keep it at 3.4 4 3.13 that once again depends upon the

once again depends upon the manufacturer. Best is to get these kinds

manufacturer. Best is to get these kinds of information from the OEM who is

of information from the OEM who is supplying these batteries.

PPT I will circulate that is that uh that is all right.

TVS diodes are transient voltage suppressor diodes. Those are essentially

suppressor diodes. Those are essentially to protect your battery cell from

to protect your battery cell from transient voltages. sudden spike of

transient voltages. sudden spike of voltages they shouldn't damage the

voltages they shouldn't damage the battery cell. So you can use these TVS

battery cell. So you can use these TVS diodes everywhere anywhere wherever

diodes everywhere anywhere wherever these transient suppressions transient

these transient suppressions transient uh safety is required protection is

uh safety is required protection is required. So in this case we have used

required. So in this case we have used TVS diodes for protecting ourself from

TVS diodes for protecting ourself from transient voltages.

Okay, we will close this session. We will meet in the afternoon.

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YouTube Transcript:Embedded Systems and Design & Development - Feb 17, 2026 | Morning | VisionAstraa EV Academy