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Electronic load control feedback loop - Use ACS712?
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SpottedDick:

--- Quote from: MarkF on June 21, 2022, 04:38:00 pm ---You are missing the elephant in the room.

You will NOT be able to sink 20A through one MOSFET

--- End quote ---

You're way off topic here. This topic is just on the feedback circuit. It's actually 6 MOSFETs I'm driving, but again, not relevant, I just want to understand the feedback portion of the circuit. I posted a thermal image of them recently on this forum if you'd like a look.




--- Quote ---Who's Tom?
--- End quote ---



Sorry Tim :)

Also, thanks for the info also contained in your post
T3sl4co1l:
Also BJTs are reasonable down here, food for thought:
https://www.eevblog.com/forum/projects/why-are-mosfets-used-as-pass-elements-in-linear-power-supplies/msg3531820/#msg3531820

Tim
MarkF:

--- Quote from: SpottedDick on June 21, 2022, 04:47:08 pm ---
--- Quote from: MarkF on June 21, 2022, 04:38:00 pm ---You are missing the elephant in the room.

You will NOT be able to sink 20A through one MOSFET

--- End quote ---

You're way off topic here. This topic is just on the feedback circuit. It's actually 6 MOSFETs I'm driving, but again, not relevant, I just want to understand the feedback portion of the circuit. I posted a thermal image of them recently on this forum if you'd like a look.

--- End quote ---

The feedback circuit is simple.  The op-amp will drive the MOSFET until the voltage across the sense resistor equals the voltage at (+) input of the op-amp (i.e. it will make the (+) input and (-) input equal).  You calculate everything from there.  I used a 10:1 voltage divider on the op-amp input giving 0v to 0.5v at the (+) input; resulting in 0.5v across the sense resistor; giving 2.5A using a 0R200 resistor.

By-the-way:  you're going to have issues if the DUT is not connected or powered off.

PS:  I saw your thermal images and it appears you are not driving the parallel MOSFETs correctly.   :-//
You never show how they are paralleled.
T3sl4co1l:

--- Quote from: MarkF on June 21, 2022, 05:06:28 pm ---PS:  I saw your thermal images and it appears you are not driving the parallel MOSFETs correctly.   :-//
You never show how they are paralleled.

--- End quote ---

I'm guessing that was naively, hence the present direction (control per).

Tim
SpottedDick:
Nope, I'm attempting control in parallel. I will detail my failure here if it completely falls to bits :D

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