| Electronics > Repair |
| 18V/3A HY1503 PSU - weird CC/CV behavior while charging battery cells |
| << < (13/15) > >> |
| iMo:
So, I have wired together the in- with its out at both spare opamps in the TL084, and their in+ to ground (the ground in the schematics). The CV and CC wiring remains as the latest above. The load is the ww resistor and it gives 2.27A at 18.7V (the max PSU voltage here) with CC disengaged. After power up the PSU I can see aprox 10mVpp 300ns period oscillation (probe 1x, AC, BW limit off) at the CC opamp's output, which is slowly dropping down (within 5-10secs) into the noise of my Rigol 1062CA (perhaps 1-2mVpp). That is with the CC disengaged. With engaged CC I see clean output (<2mVpp noise). The output of the 741 is clean. In the lower portion of spectra I can see 5mVpp saw tooth ripple w/ 10ms period at the CC opamp's output, and 7.5mVpp at the CV opamp's output. The ripple increases a bit (30mV) when going to CC's zero current output. The above oscillation is superimposed on this ripple. The 10mVpp 300ns oscillation at the CC opamp's output appears always when doing abrupt changes, it slowly disappears into the background noise after couple of seconds. So I will leave it now and will have a look at it tomorrow, what is new there as it lives its own life, it seems :) |
| iMo:
Some shots from this morning.. Immediately after the cold start the oscillation (2.3A/18.7V CC disengaged) was as below. It lasted for about 30-40min without disappearing. Afterwards after re-inserting the load the effect of slow disappearing started again. The 741 CV output is clean - see below the ripple. With CC engaged I do not see oscillation. The CC output is DC 11.56V with disengaged. I replaced the original 100p capacitor in the CC fb with 120p C0G, but it did not help. Cleaned with IPA couple of times. The oscillation is visible at the output posts as well. Probe Tek 1x, BW off, AC, no oscillation or ripple seen with probe's gnd and input put on the same node at PSU. It seems the rising edge of the ripple starts the oscillation burst (it reminds me on my experiments with superregeneration :) ), the oscillation somehow depends on the temperature, the effect of disappearing with 5-10sec time constant leads to some thermal effect or leakage or?? |
| xavier60:
Post a schematic of how everything is. The LM741 has been replaced? Also, a load transient test might show if there is loop instability. |
| iMo:
Below the mod v5 schematics. There is one thing which may cause the instability - the 200mA/3A switch is mounted on the front panel, shorting the 4R7 for 3A (aprox). The leads are thick, but aprox 15cm (!!) long coming to the shunt on the pcb. That may cause some HF feedback.. I will doublecheck that later on.. Ideally I planned to place a relay near the shunt with the 4R7, but there is small space for it and of course the laziness.. ::) |
| xavier60:
If you plan to do the load transient test, go ahead. If not, remove the 330pF from across the 741's inputs. Put a 1nF capacitor or higher between its output and Inverting input. The 10K between the Inverting input and GND must be left in place. |
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