Electronics > Repair
18V/3A HY1503 PSU - weird CC/CV behavior while charging battery cells
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xavier60:

--- Quote from: iMo on September 20, 2024, 08:20:37 am ---The signal at the in- is the ~same as the output (10n fb cap), in+ is clean.

Touching the CC's in- or output decreases ampl to 400mVpp and period increases to 800ns.

Other 324 pins incl 741's pins do not show any relevant impact.

Transistors - the touching of the base of the first transistor - the same change as with in-/out of the CC opamp, other points around the transistors - no relevant impact.

--- End quote ---
Have you tried another opamp?
iMo:
With the D12 disconnected the amplitude at the CC opamp's output is 800mVpp period 750ns.

The replacing the 324 will be the last step :)
Nope, I will do it now, I put there a socket..
iMo:
So - I've desoldered the 324, it is TI's LM324.
Soldered in the gold plated socket. I have not found the 324 in my junkbox, so now using TL084 (TI).

CV - as in my schematics.

CC - 100pF in the fb (orig one from top side) and 1k5 to shunt sense, added a 100nF decoupling

The circuit behaves differently:

1. with CC engaged no oscillation, noise below 20mVpp at CC's opamp output
2. with CC disengaged and loaded (2.2A, 18.7V):
a. when PSU switched on there is 30-40mVpp 270ns period oscillation at CC's output, it slowly decreases to 20mVpp, sometimes disappears (noise below 10mV at CC's opamp output) and appears, it disappears when touching output of the 741 or the feedback of the 741
b. when the load is reinserted (2.2A 18.7V) the oscillation starts again at 30-40mVpp, then within aprox 15secs its amplitude goes down and disappears (noise below 10mV at CC's output), but still sensitive..

3. after 40minutes when the board is already hot the CC's opamp output shows 20mVpp 150ns period oscillation CC engaged or disengaged..

The TL084 gets pretty hot (+12/-12V).

A really mysterious stuff, indeed :)

I have here a different 084 and a TLC274, I will also try to find a 324 somewhere as well..
xavier60:
Keep in mind that the opamp for the inactive mode should have its output at maximum + voltage, about 11V and not capable of producing any output signal.
iMo:
It might come from the 741 via the diode's capacitance (the 084's output is not zero impedance), even though those frequencies are rather odd for that circuit. Later on I will continue (perhaps I would socket the 741 too) - it is enough for today.. Thanks!

PS: next step - to handle the inputs of the two not used opamps in the package, perhaps they mess up..
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