Electronics > Beginners

Pratical Hardware Questions for DIY Electronic Load

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brabus:
You can connect them to GND no problem whatsoever. I would in any case keep the resistors, you may need to patch some wire or try something exotic on your board, so having a clean way to break the ground connection can be useful.

Mechatrommer:

--- Quote from: schmitt trigger on September 19, 2018, 04:36:11 pm ---Very interesting concept to include an external waveform generator input, to provide a a variable load to -let's say- test the a PSU stability.  :-+

The maximum frequency would, of course, be limited to the frequency response limited by the integrating capacitor in the feedback loop.

--- End quote ---
the concept is more suited to 4 quadrant PSU/Load supply. with 1 quadrant load, you have to limit the FG signal to 1st quadrant region only. and you need to stick the V to A conversion formula in mind when adjusting FG magnitude so shunt wont go outside that region.

t1d:
Thanks, guys, that's good information. I will give it some thought.

I have thought, a little, about the FG magnitude... I have looked at a few limiter and compressor circuits, but I have not designed anything, yet... They can be complex.

A 2.5v zener could be used, but wouldn't that clip the signal? Might that work as a cheap and easy warning and give some protection? You could see it on an oscilloscope...

Do you have any suggestions, for a circuit type name, that I could research?

jrsikken:
For your inspiration please take a look at my design.

https://github.com/jrsikken/ElectronicLoadR3

It uses a DAC to set the current, the MCP4725. Pretty cheap and 12bit.

I have tuned the constant current circuit (opamp+mosfet+currentsensefeedback) for fastest response. It settles in 20us. So it can do pulsed load. Using my embedded code it can do 3kHz square wave, or pulses that are 156us wide.

Yesterday I have tried someone's sketch that overclocks the MCP4725 DAC and it generates a 3kHz sinus. Sample rate is 60kHz. The values for the sines are simply looked up from an array in program memory. I have modified the sketch to generate a 6kHz square wave, or pulses that are 78us wide.

What I am trying to say is that the MCU can also be a function generator that can generate any wave shape, and then you don't need external signal generator.

Regarding opamps, I started with MCP6002 and later I changed to MCP6072. I did not need to use input current bias resistor because current is extremely low. I changed to MCP6072 to reduce the offset error and to make the output voltage swing to GND as low as possible.

ogden:

--- Quote from: jrsikken on September 26, 2018, 01:51:34 pm ---For your inspiration please take a look at my design.

https://github.com/jrsikken/ElectronicLoadR3

--- End quote ---

Please do not assume that everybody uses Eagle or have it installed on phones/tablets they often use to read news & forums. It is advised to provide information in more popular file formats like PDF, PNG, JPG. Could you show schematics as picture attached to forum post?

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