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10A 0.1V CC source for handheld DIY microohm-meter

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Is using direct transformer output for the 10A and measuring AC Voltage instead at all possible?

I have built a decent milliohm meter, however I used 100mA instead of 10A.
You have basically 4 blocks:
1. 100mA current source, using a precision voltage reference and opamp + p channel MOSFET. This is a very common and typical.
2. Op amp square wave oscillator set to 40Hz.
3. H bridge, to alternate the current (basically converting it to AC). This is to measure at ~40Hz. This allow you to only measure AC and get rid of any dc noise and improve noise rejection. (At least in theory).
4. AD620 instrumention amplifier is sensing across resistor under test, with a gain of 10. Output is the 1Vac / 1Ohm. This foes through a resisor (possibly increasing phase margin) to a common DMM.

This worked great for me. I was able to measure very low resistance with good accuracy

For top efficiency look for a buck converter with synchronous rectification, otherwise diode loss will be ~0.3V and 3W even if you go with Schottky. That's still not as bad as a completely linear solution, but not optimal.

If you don't mind 12W of heat in exchange for a very simple circuit, build the linear current source powered by a few NiMH cells in parallel.

Terry Bites:
 What you need here is a 1V regulated supply with a switchable current limit. You might want a skim of TI's SNVA829 (June 2018) ap note
Have you consdered a less brute force micro-ohm meter? Lower current better voltage sensing? www.maximintegrated.com/en/design/technical-documents/app-notes/1/106.html

I built a fairly inexpensive milliohm meter as an exercise to see how low I could measure with decent accuracy. I have some videos of it on Youtube. Main sources of error I would say are temperature variation and gain drift. Auto-zero works quite well.


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