Electronics > Beginners
LM317 Dummy load circuit
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VEGETA:

--- Quote from: Ian.M on April 21, 2018, 12:04:25 am ---That sounds like the OPAMP is bad, or maybe its +9v supply is missing or you've got its pinout wrong.  In normal operation its In- would be within a couple of mV of its In+ (always true of a working OPAMP in a steady state condition if its in its linear region of operation: i.e. the output isn't stuck up against one of its supply rails).  As In+ is grounded, that means In- should measure as 0V.

Photos please.

If connected as shown, with the LM317 module feeding it set to +2.5V, the pot should vary the voltage at its wiper, Vc, between +2V and +2.5V
Also,  work your way round all the OPAMP pins checking the voltage with respect to Gnd, and post the voltage at each pin, with Vc set to 2.5V.  We'll also need the OPAMP part number if it isn't easily readable in the photo.

Got any spare OPAMPs?

--- End quote ---

My opamp lis LM358 but it is SMD version which is so tiny that I had to spend 2 hours soldering wires to it. I suspect that it is the cause of this issue since there are no other way according to what we achieved. I have ordered lm358 and lm324 DIP version but they need another month to arrive. Perhaps I should just postpone the project until then because spending 5 hours debugging a simple circuit like this with dodgy part is not a funny thing.

If you are interested in voltages, I told you the In- pin is -8v always... maybe it is shorted to GND pin or something. I will check tomorrow if I could get a better result or re-solder it a better way. I have ordered SMD to DIP adapters too for such situations.
VEGETA:
For now, I have started a new topic here: https://www.eevblog.com/forum/beginners/dc-dummy-load-circuit-calibration/

It is about using an N-MOSFET with op-amp... it still has one small problem that I would like you to take a look at it.

regards
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