Author Topic: Electronic loads and loads  (Read 1403 times)

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Offline PerranOakTopic starter

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Electronic loads and loads
« on: December 14, 2019, 08:37:50 pm »
I would quite like to build an electronic load: a fun project, I imagine.

Something small and simple: up to an amp-ish and, say, up to 20V-ish.

Does anyone know of a good project/schematic they could recommend please?
You can release yourself but the only way to go is down!
RJD
 

Offline MarkF

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Re: Electronic loads and loads
« Reply #1 on: December 14, 2019, 09:17:48 pm »
This is what I built:

889728-0

890888-1



Also check out J_Diddy_B's project:
   https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/
« Last Edit: December 16, 2019, 11:15:20 pm by MarkF »
 

Online Kleinstein

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Re: Electronic loads and loads
« Reply #2 on: December 14, 2019, 10:12:46 pm »
One should get away without the trimmer for the reference. One may also get away without the buffer after the pot.


On the other side it may be a good idea to limit wind up in case the voltage drops too low. This could be something like an OP limiting the set voltage at the switch to something like 3 times the load voltage. At low voltages the load would than turn over from constant current to constant resistance (e.g. 3 x the shunt, should be larger than shunt + FET R_on + Amp-meter).
 

Offline MarkF

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Re: Electronic loads and loads
« Reply #3 on: December 14, 2019, 11:00:40 pm »
One should get away without the trimmer for the reference. One may also get away without the buffer after the pot.

Right.  I have not populated the trim pot.  It's just on the PCB in case.
The op-amp buffer after the voltage reference uses the 2nd op-amp in the dual package.  It probably is not needed either.
Edit:  Without the op-amp buffer, the 10:1 voltage divider would be affected since the pot value is so near the voltage divider values.

Quote
On the other side it may be a good idea to limit wind up in case the voltage drops too low. This could be something like an OP limiting the set voltage at the switch to something like 3 times the load voltage. At low voltages the load would than turn over from constant current to constant resistance (e.g. 3 x the shunt, should be larger than shunt + FET R_on + Amp-meter).

Sorry, I don't understand what you are getting at.
Maybe show a circuit...
« Last Edit: December 14, 2019, 11:36:14 pm by MarkF »
 

Offline PerranOakTopic starter

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Re: Electronic loads and loads
« Reply #4 on: December 16, 2019, 03:09:28 pm »
Cheers mate.

What's "REF02"?
You can release yourself but the only way to go is down!
RJD
 

Offline Ysjoelfir

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Re: Electronic loads and loads
« Reply #5 on: December 16, 2019, 03:11:44 pm »
Cheers mate.

What's "REF02"?
REF02 is a rather cheap but quite good 5 Volts voltage reference.
https://www.ti.com/lit/ds/symlink/ref02.pdf
Greetings, Kai \ Ysjoelfir
 
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Offline magic

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Re: Electronic loads and loads
« Reply #6 on: December 16, 2019, 04:42:06 pm »
That's overkill. My active load uses a 2.4 zener (and those things are absolutely horrible in terms of stability wrt to temperature and bias current) and it still stabilizes to 1% of its long term load within seconds after adjusting the pot. And I run the power darlington's base current trough it since it also generates a virtual ground :scared:

I suspect a TL431 would be about as good as anything in this application. The spec is less than 0.65% drift over 0~70°C temperature range, 0.25% typical.
 


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