Alternate components for a project.

Thread Starter

zophas

Joined Jul 16, 2021
111
Ok. So I have decided to try a project from AAC. The project is a Battery operated 1 amp current source posted by someonesdad in 2011. The info is in Completed Projects under Power Supplies. Now some of the components are either obsolete or not available in my country (South Africa). So I have the following questions: Can I replace the Max872 with a LM336Z-2.5? Can I replace the Max480 with a TL071CP? Type "C' cells are very difficult to find in SA, can I use a AA cell instead? The 0.2 Ohm resistor does not show a Watt rating neither does does the poster talk about it in his PDF. Can I use a 0.22 3W Silicone Wirewound for that? Thanks.

Edit: Sorry, don't know how to post a link.
 
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LowQCab

Joined Nov 6, 2012
1,078
"There's more than one way to skin a Cat"
If You would simply tell us what You are trying to accomplish,
I'm sure You will get at least ~10 different suggestions.
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dl324

Joined Mar 30, 2015
13,078
Post a schematic so we can see what you're talking about.
Type "C' cells are very difficult to find in SA, can I use a AA cell instead?
You'd be better off using D cells.

EDIT: Found the circuit:
1627182103791.png
There's nothing special about the voltage reference. You could use a zener diode if you don't need the temperature stability.

The pot doesn't need to be a 10 turn.

You can use any opamp as long as the input and output voltage ranges are sufficient.

If you replace the MOSFET with a BJT, you'll have more options for opamp and the 1k gate resistor can be omitted. The 1k resistor from the source to the inverting input isn't necessary.

The current sensing resistor doesn't need to be wirewound. Anything a half watt or larger would work. At 1A, it will dissipate 200mW.

Didn't read enough of the PDF to find out what the battery was for. It's not needed for a current source. EDIT: Duh, it's the current source supply... Drawing it on it's side threw me...
 
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Thread Starter

zophas

Joined Jul 16, 2021
111
Post a schematic so we can see what you're talking about.
You'd be better off using D cells.

EDIT: Found the circuit:
View attachment 244345
There's nothing special about the voltage reference. You could use a zener diode if you don't need the temperature stability.

The pot doesn't need to be a 10 turn.

You can use any opamp as long as the input and output voltage ranges are sufficient.

If you replace the MOSFET with a BJT, you'll have more options for opamp and the 1k gate resistor can be omitted. The 1k resistor from the source to the inverting input isn't necessary.

The current sensing resistor doesn't need to be wirewound. Anything a half watt or larger would work. At 1A, it will dissipate 200mW.

Didn't read enough of the PDF to find out what the battery was for. It's not needed for a current source.
Thanks for the input. I would like to use this for measuring low resistances. It's for another project I am working on.

Edit: I can get a "D" cell but the cost would make the project not worth while, perhaps I could use AA cells in series?
 
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Thread Starter

zophas

Joined Jul 16, 2021
111
AA cells will struggle to supply 1A for long. You would be better off with wall wart.
I was hoping to keep the portability option. Can anyone explain to me the role the two batteries play in this circuit?
Can parallel AA's simulate a "C" cell?
 

LesJones

Joined Jan 8, 2017
3,472
The 9 volt battery just supplies power to the op amp. The battery of "C" cells supplies the output current.
It would require about 3.5 "AA" cells to give the same capacity as a "C" cell.

Les.
 

Thread Starter

zophas

Joined Jul 16, 2021
111
The 9 volt battery just supplies power to the op amp. The battery of "C" cells supplies the output current.
It would require about 3.5 "AA" cells to give the same capacity as a "C" cell.

Les.
Thank you, @LesJones . I think I have enough info to give this circuit a try. Now I just gotta find some money for the parts. Lol.
 

Audioguru again

Joined Oct 21, 2019
3,499
The minimum supply for a TL071 is 7V. On the datasheet TI recommends a minimum of 10V.
Its inputs must never go below 4V above its negative supply or never go above 4V below its positive supply.
You must use a modern "rail to rail" opamp in this circuit. EDIT: But one opamp in an LM358 dual opamp will work.

The datasheets for AA alkaline batteries show that they have a lot of trouble producing 1A. I think they will overheat as the voltage drops very quickly.
 

Attachments

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Thread Starter

zophas

Joined Jul 16, 2021
111
The minimum supply for a TL071 is 7V. On the datasheet TI recommends a minimum of 10V.
Its inputs must never go below 4V above its negative supply or never go above 4V below its positive supply.
You must use a modern "rail to rail" opamp in this circuit. EDIT: But one opamp in an LM358 dual opamp will work.

The datasheets for AA alkaline batteries show that they have a lot of trouble producing 1A. I think they will overheat as the voltage drops very quickly.
Good news about the op-amp. I saw a LM358 in my parts box today. As far as the battery is concerned I am considering using 4 AA in parallel to simulate a "C" cell. I don't know too much about opamps but I think I am in the right place (AAC) to find out more about them. Thanks.
 

AlbertHall

Joined Jun 4, 2014
11,498
Well the circuit shows a type "C" battery which is 1.5v. I am not experienced enough to know if I can just put a 3.7v battery in it's place.
The diagram shows a two cell battery which would be 3V. What load do you want to supply with the 1A current?
 

Thread Starter

zophas

Joined Jul 16, 2021
111

LowQCab

Joined Nov 6, 2012
1,078
The Voltage of the Battery is almost irrelevant.
The Battery needs to be able to deliver a ton of Current,
to generate a large enough Voltage across the Load to get an accurate measurement.

A RC-Hobby Li-Po Battery is the ideal direction to go in,
but several Li-Ion Batteries will also work,
even though they are not designed to deliver as much Current as Li-Po's are.

You can probably reliably get 1-Amp per Li-Ion Cell,
so 10 of them, all hooked-up in parallel,
will reliably deliver roughly 10-Amps with no troubles.

Here's what You need .............
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Current Standard FLAT .png
 
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