I have just completed an Electronic Load project based on a Chinese 150W/10A/72V LM324 four MOSFET kit:
https://www.ebay.com.au/itm/150W-Constant-Current-Electronic-Load-Discharge-Capacity-Tester-DIY-Kit/173078658449?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2648A 3.7v LiPo isolates and drives the LED panel meter. An LM317 is used as a manual fan speed control. Jiffy box measures 155 x 95 x 55mm.
I downgraded the wattage to <75 watts because of the CPU heatsink and to 33v max and 3A max based on the LED panel meter ratings.
The unit works well and is able to hold the load steady with <0.1% variation for currents over 100mA.
I now want to build the same kit with a wider range of constant current capability, up to 10A and down to <10mA, perhaps down to 1mA.
The basic design uses an LM324 quad Op Amp to control four To220 MOSFETs through 0.22 ohm sensing resistors. The 4 current paths are paralleled at the input.
The new design is to have several input sockets and use
different current sensing resistors for each range. I will aim for up to 100W max load for now.
The first MOSFET would have a 5 ohm current sensing resistor and control currents up to 100mA
The second MOSFET would have a 0.5 ohm current sensing resistor and control currents up to 1A
The 3rd and 4th MOSFETs would have 0.1 ohm current sensing resistors each, with current paths paralleled, and control up to 10A total (5A ea).
I expect to replace the 3rd and 4th To220 MOSFETs with higher rated units capable of handling about 50w continuous load each. Suggested devices?
Any fundamental reason why this approach would not work?
Is there a better Op Amp than the LM324 for this task?
enut11
EDIT: Some of the functionality above has been incorporated into the original CC Load as as result of my experiments.
Take #2 CC Load, which is discussed later in this thread (from Reply #8), will be aimed at the original advertised specs of 150W and 10A but limited to around 30v max.