| Electronics > Repair |
| 18V/3A HY1503 PSU - weird CC/CV behavior while charging battery cells |
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| xavier60:
I wasn't having much fun at all until I realized that I shouldn't have omitted the 10 ohm Base stopper resistor. For the compensation, a 2.2K and 150pF gave fast stable response, 3us. Just a 470pF gave a slower stable response, 10us. As I discovered, it's possible to have oscillations in localized areas other than the whole loop. |
| xavier60:
470pF and 2.2K improves tolerance to capacitive loads. First is a load transient test with a 470uF POSCAP directly across the output. Then with a 0.1 ohm in series with the POSCAP. The trace is inverted as I'm looking at the negative output WRT +Ground. |
| iMo:
I disconnected the 330p at 741's inputs and wired 100ohm in parallel to the 1k at BE of the 2N3055. It did not help with jumping voltage at switching ~10ohm load on/off. I returned the 330p between the 741's inputs and the jumping voltage is gone. PS: as you are well equipped - could you try the 100pF between pin5 and pin6 of the 741 as in the original - how it affects stuff, plz?? PPS: below the transient at the posts when I switch in a resistor, 15V/1.9A. .. and the 741's output, the oscillation might come from a longer lead. |
| xavier60:
I'm using an LM358. Even a 1000pF across the input only caused a small amount of ringing. With a 470pF and 2.2K, mine settles in 10us. That high frequency ringing could be coming from the wiring to your shorter. |
| xavier60:
Your LM741 might be faulty if it's very old. I have seen old opamps randomly develop large input offsets. |
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