# simulating adjustable voltage sources in series

• posted

does anyone know how I could make a circuit that would behave similar to a = bunch of batteries in series, but where I could control the voltage of each= battery?

at first I thought this would be easy... but I haven't been able to come up= with anything.

picture, let's say 10 AA batteries in series, 1.5V each, now if I could in = some way control each voltage without impacting the other batteries, let's = say I use a digital pot somehow to adjust the voltage on one of the batteri= es to 0.5V. All the other batteries should stay at 1.5V and if I had a DMM= across each battery I should only see the one battery drop in voltage...

My problem is that everything I think of always causes a change in one of t= he other batteries (this is because the positive of one battery is the nega= tive of the other) I've thought of maybe some kind of adjustable zener... e= ven found this guy

who seemed promising, but once I daisy chain them... well, I just don't see= them working if they are in serial like I need them. I'm picturing a stri= ng of 5V zeners all being used to power whatever circuits I come up with to= mimic the batteries...

any thoughts would be appreciated! thanks!

• posted

bunch of batteries in series, but where I could control the voltage of each battery?

with anything.

way control each voltage without impacting the other batteries, let's say I use a digital pot somehow to adjust the voltage on one of the batteries to 0.5V. All the other batteries should stay at 1.5V and if I had a DMM across each battery I should only see the one battery drop in voltage...

other batteries (this is because the positive of one battery is the negative of the other) I've thought of maybe some kind of adjustable zener... even found this guy

them working if they are in serial like I need them. I'm picturing a string of

5V zeners all being used to power whatever circuits I come up with to mimic the batteries...

Only sourcing or sinking, but not both?

How much control range (the *431's will only do 2.5V minimum but there is a 1.25V version out there), and how you want to input the control? ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
• posted

bunch of batteries in series, but where I could control the voltage of each battery?

with anything.

some way control each voltage without impacting the other batteries, let's say I use a digital pot somehow to adjust the voltage on one of the batteries to 0.5V. All the other batteries should stay at 1.5V and if I had a DMM across each battery I should only see the one battery drop in voltage...

other batteries (this is because the positive of one battery is the negative of the other) I've thought of maybe some kind of adjustable zener... even found this guy

them working if they are in serial like I need them. I'm picturing a string of

5V zeners all being used to power whatever circuits I come up with to mimic the batteries...

How much current? ...Jim Thompson

```--
| James E.Thompson, CTO                            |    mens     |
• posted

bunch of batteries in series, but where I could control the voltage of each battery?

with anything.

some way control each voltage without impacting the other batteries, let's say I use a digital pot somehow to adjust the voltage on one of the batteries to 0.5V. All the other batteries should stay at 1.5V and if I had a DMM across each battery I should only see the one battery drop in voltage...

other batteries (this is because the positive of one battery is the negative of the other) I've thought of maybe some kind of adjustable zener... even found this guy

them working if they are in serial like I need them. I'm picturing a string of

5V zeners all being used to power whatever circuits I come up with to mimic the batteries...

Might be helpful to know exactly what you're trying to accomplish?

Do you need multiple simultaneous voltages? Circuits that load batteries unequally often have other issues. If it's a sensing issue, can you use one power supply an just simulate the sense voltages?

Might be easier to build 10 power supplies and let a microcontroller figger out all the other voltages when you change one. Oughta be able to get by with one D/A and 10 sample/hold amps.

Don't forget to consider the turn on/off transients in your system.

• posted

The subject title is a little illusive. I say this because I can't tell if he means he needs to know how to do this in a simulator or actually do this on the bench?

Also, no comment as to the load handling abilities?

Isolated supplies is basically the requirement here from what I can see.

If the idea is to play with a divider string where one item in the string can be varied and the voltage around the others has to remain constant? Then, I see a current loop scenario. A current source that needs to maintain a fix amount of current so that the other dividers will continue to display the same voltage.

Jamie

• posted

So you just want a string? Like, N cells at 1.5V, with one additional cell being variable (0.5-1.5 say)? This is absolutely identical to a source of

1.5*N + 0.5 volts with a 0-1V source in series. Basic superposition.

Tim

```--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms```
• posted

bunch of batteries in series, but where I could control the voltage of each battery?

with anything.

way control each voltage without impacting the other batteries, let's say I use a digital pot somehow to adjust the voltage on one of the batteries to 0.5V. All the other batteries should stay at 1.5V and if I had a DMM across each battery I should only see the one battery drop in voltage...

other batteries (this is because the positive of one battery is the negative of the other) I've thought of maybe some kind of adjustable zener... even found this guy

them working if they are in serial like I need them. I'm picturing a string of

5V zeners all being used to power whatever circuits I come up with to mimic the batteries...

"Real world"? Or just simulation?

If "Real world", how much load current? ...Jim Thompson

```--
| James E.Thompson, CTO                            |    mens     |
• posted

a bunch of batteries in series, but where I could control the voltage of ea= ch battery?

up with anything.

n some way control each voltage without impacting the other batteries, let'= s say I use a digital pot somehow to adjust the voltage on one of the batte= ries to 0.5V. All the other batteries should stay at 1.5V and if I had a D= MM across each battery I should only see the one battery drop in voltage...

the other batteries (this is because the positive of one battery is the ne= gative of the other) I've thought of maybe some kind of adjustable zener...= even found this guy

ee them working if they are in serial like I need them. I'm picturing a st= ring of 5V zeners all being used to power whatever circuits I come up with = to mimic the batteries...

sorry if my question was unclear. I would like to control every "simulated= battery" voltage. And the only load they will see will be that of the vol= t meter, so they hardly have to be able to source anything, I just want to = read the voltages on them. My only criteria is that they are in series and= that there is a volt meter taking a reading across each one, and when you = change the voltage on one it doesn't change on the other meters.

i don't know how i'll control the voltages yet, i would guess a digital pot= some how, but my problem is that i can't think of a way to do this... and = i don't mean in any detail, just in a general sense... like a basic sketch = of how this might be accomplished... because the reference point of one vol= tage will also be the "hot" point of the next voltage in series... so when = I adjust a voltage I'm also shifting the reference point of the next voltag= e=20

I guess I could some fancy programming that worked out the math to adjust a= ll other voltages when one is moved. For example if this was just a string= of variable resistors (a long voltage divider) you could have a program th= at would adjust all other resistor values to keep their voltage constant wh= enever you change the voltage on one.... but there's gotta be a better, mor= e hardware based solution...

thanks

• posted

bunch of

with

some way

All the

should

other

guy

them

sorry if my question was unclear. I would like to control every "simulated battery" voltage. And the only load they will see will be that of the volt meter, so they hardly have to be able to source anything, I just want to read the voltages on them. My only criteria is that they are in series and that there is a volt meter taking a reading across each one, and when you change the voltage on one it doesn't change on the other meters.

i don't know how i'll control the voltages yet, i would guess a digital pot some how, but my problem is that i can't think of a way to do this... and i don't mean in any detail, just in a general sense... like a basic sketch of how this might be accomplished... because the reference point of one voltage will also be the "hot" point of the next voltage in series... so when I adjust a voltage I'm also shifting the reference point of the next voltage

I guess I could some fancy programming that worked out the math to adjust all other voltages when one is moved. For example if this was just a string of variable resistors (a long voltage divider) you could have a program that would adjust all other resistor values to keep their voltage constant whenever you change the voltage on one.... but there's gotta be a better, more hardware based solution...

thanks

---------------------------------- Use a current source to feed your string of variable R's instead of a voltage source. Art

• posted

bunch of batteries in series, but where I could control the voltage of each battery?

with anything.

some way control each voltage without impacting the other batteries, let's say I use a digital pot somehow to adjust the voltage on one of the batteries to 0.5V. All the other batteries should stay at 1.5V and if I had a DMM across each battery I should only see the one battery drop in voltage...

other batteries (this is because the positive of one battery is the negative of the other) I've thought of maybe some kind of adjustable zener... even found this guy

them working if they are in serial like I need them. I'm picturing a string of

5V zeners all being used to power whatever circuits I come up with to mimic the batteries...

battery" voltage. And the only load they will see will be that of the volt meter, so they hardly have to be able to source anything, I just want to read the voltages on them. My only criteria is that they are in series and that there is a volt meter taking a reading across each one, and when you change the voltage on one it doesn't change on the other meters.

some how, but my problem is that i can't think of a way to do this... and i don't mean in any detail, just in a general sense... like a basic sketch of how this might be accomplished... because the reference point of one voltage will also be the "hot" point of the next voltage in series... so when I adjust a voltage I'm also shifting the reference point of the next voltage

other voltages when one is moved. For example if this was just a string of variable resistors (a long voltage divider) you could have a program that would adjust all other resistor values to keep their voltage constant whenever you change the voltage on one.... but there's gotta be a better, more hardware based solution...

It sounds like you want to add up a string of numbers, change one of them, and have the sum not change. That doesn't work.

• posted

bunch of

with

some way

All the

should

other

guy

them

battery"

they

them.

taking a

change on

some how,

any

"hot"

shifting

other

all

voltage

Yep. That is the correct answer. ...Jim Thompson

```--
| James E.Thompson, CTO                            |    mens     |
• posted

to a bunch of batteries in series, but where I could control the voltage of= each battery?

me up with anything.

d in some way control each voltage without impacting the other batteries, l= et's say I use a digital pot somehow to adjust the voltage on one of the ba= tteries to 0.5V. All the other batteries should stay at 1.5V and if I had = a DMM across each battery I should only see the one battery drop in voltage= ...

of the other batteries (this is because the positive of one battery is the= negative of the other) I've thought of maybe some kind of adjustable zener= ... even found this guy

t see them working if they are in serial like I need them. I'm picturing a= string of 5V zeners all being used to power whatever circuits I come up wi= th to mimic the batteries...

ted battery" voltage. And the only load they will see will be that of the = volt meter, so they hardly have to be able to source anything, I just want = to read the voltages on them. My only criteria is that they are in series = and that there is a volt meter taking a reading across each one, and when y= ou change the voltage on one it doesn't change on the other meters.

pot some how, but my problem is that i can't think of a way to do this... a= nd i don't mean in any detail, just in a general sense... like a basic sket= ch of how this might be accomplished... because the reference point of one = voltage will also be the "hot" point of the next voltage in series... so wh= en I adjust a voltage I'm also shifting the reference point of the next vol= tage=20

t all other voltages when one is moved. For example if this was just a str= ing of variable resistors (a long voltage divider) you could have a program= that would adjust all other resistor values to keep their voltage constant= whenever you change the voltage on one.... but there's gotta be a better, = more hardware based solution...

The sum can change, if I have 3 5V batteries in series that's 15V if I chan= ge one to 3V then that's 13V.... I just want the other to remain constant. =

• posted

bunch of

with

some way

a

All the

should

the other

the

this guy

them

5V

battery"

they

them.

taking a

change on

some how,

in any

"hot"

shifting

other

all

voltage

I think that's it, that sounds pretty good. Thanks!

• posted

bunch of batteries in series, but where I could control the voltage of each battery?

up with anything.

some way control each voltage without impacting the other batteries, let's say I use a digital pot somehow to adjust the voltage on one of the batteries to 0.5V. All the other batteries should stay at 1.5V and if I had a DMM across each battery I should only see the one battery drop in voltage...

the other batteries (this is because the positive of one battery is the negative of the other) I've thought of maybe some kind of adjustable zener... even found this guy

see them working if they are in serial like I need them. I'm picturing a string of 5V zeners all being used to power whatever circuits I come up with to mimic the batteries...

battery" voltage. And the only load they will see will be that of the volt meter, so they hardly have to be able to source anything, I just want to read the voltages on them. My only criteria is that they are in series and that there is a volt meter taking a reading across each one, and when you change the voltage on one it doesn't change on the other meters.

some how, but my problem is that i can't think of a way to do this... and i don't mean in any detail, just in a general sense... like a basic sketch of how this might be accomplished... because the reference point of one voltage will also be the "hot" point of the next voltage in series... so when I adjust a voltage I'm also shifting the reference point of the next voltage

all other voltages when one is moved. For example if this was just a string of variable resistors (a long voltage divider) you could have a program that would adjust all other resistor values to keep their voltage constant whenever you change the voltage on one.... but there's gotta be a better, more hardware based solution...

one to 3V then that's 13V.... I just want the other to remain constant.

But that's the way that batteries work. Changing one doesn't change the drop across the others, but it changes the series total.

Are you using some simulator that forces all the voltage sources to be the same? I don't understand the problem.

Are you trying to design, or simulate, a stack of voltage sources which are independently controllable?

• posted

You use a difference measurement, not a "measurement probe" that reads the voltage with respect to ground. Or use two and mentally subtract them.

Tim

```--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms```
• posted

ar to a bunch of batteries in series, but where I could control the voltage= of each battery?

come up with anything.

ould in some way control each voltage without impacting the other batteries= , let's say I use a digital pot somehow to adjust the voltage on one of the= batteries to 0.5V. All the other batteries should stay at 1.5V and if I h= ad a DMM across each battery I should only see the one battery drop in volt= age...

one of the other batteries (this is because the positive of one battery is = the negative of the other) I've thought of maybe some kind of adjustable ze= ner... even found this guy

on't see them working if they are in serial like I need them. I'm picturin= g a string of 5V zeners all being used to power whatever circuits I come up= with to mimic the batteries...

ulated battery" voltage. And the only load they will see will be that of t= he volt meter, so they hardly have to be able to source anything, I just wa= nt to read the voltages on them. My only criteria is that they are in seri= es and that there is a volt meter taking a reading across each one, and whe= n you change the voltage on one it doesn't change on the other meters.

al pot some how, but my problem is that i can't think of a way to do this..= . and i don't mean in any detail, just in a general sense... like a basic s= ketch of how this might be accomplished... because the reference point of o= ne voltage will also be the "hot" point of the next voltage in series... so= when I adjust a voltage I'm also shifting the reference point of the next = voltage=20

just all other voltages when one is moved. For example if this was just a = string of variable resistors (a long voltage divider) you could have a prog= ram that would adjust all other resistor values to keep their voltage const= ant whenever you change the voltage on one.... but there's gotta be a bette= r, more hardware based solution...

hange one to 3V then that's 13V.... I just want the other to remain constan= t. =20

i think we're saying the same thing, and i agree with you, and that is what= i want, change one, which doesn't change the others which does change the = series total. exactly. and a constant current source running through a bunc= h of pots in series, i think would do just that.

• posted

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i'm nor sure what you mean, but my criteria is that there is a dmm tak> "panfilero"=20

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• posted
[snip]

differential measurement across each "simulated battery", so far i'm liking the current source idea.... seems like a howland constant current source with a chain of variable resistors would do the trick.

[snip]

A Howland current source is likely to give you grief... headroom.

Use a more conventional PNP plus OpAmp.

I'd draw up a schematic, but I have to run out to Southern Californica right now. Back late this PM. ...Jim Thompson

```--
| James E.Thompson, CTO                            |    mens     |
• posted

g a differential measurement across each "simulated battery", so far i'm li= king the current source idea.... seems like a howland constant current sour= ce with a chain of variable resistors would do the trick.