Timeline for Repairing power circuit with reverse polarity damage
Current License: CC BY-SA 4.0
11 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Nov 22, 2020 at 5:59 | answer | added | Dimitris | timeline score: 1 | |
| Mar 16, 2020 at 13:02 | vote | accept | UpTheCreek | ||
| Feb 21, 2020 at 2:40 | comment | added | Russell McMahon♦ | @Bimpelrekkie Yes. Also TE (or whatever it is). But the 2.5V drop across T4 *shouldn't" just be saturation. But ??? | |
| Feb 20, 2020 at 20:41 | comment | added | Bimpelrekkie | @RussellMcMahon I can't see what T4 is doing either. I also thought that it looked like a regulator but later changed my mind as indeed the feedback seems to be missing so it looks more like a switch indeed. T1 and T2 are the regulators. | |
| Feb 20, 2020 at 15:38 | comment | added | Russell McMahon♦ | @Bimpelrekkie I can't see why T4 acts as a regulator rather than an on/off switch. Can you see any obvious feedback path? | The whole cct looks vastly 'overengineered'. | |
| Feb 20, 2020 at 15:37 | comment | added | Russell McMahon♦ | /APO low turns off T5 and thus T4. It's still (so far) not obvious why it should voltage regulate. | |
| Feb 20, 2020 at 10:33 | history | edited | UpTheCreek | CC BY-SA 4.0 |
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| Feb 20, 2020 at 10:33 | comment | added | UpTheCreek | @Bimpelrekkie Ooops, thanks. I'll edit the question. Thanks for the info. | |
| Feb 20, 2020 at 10:26 | answer | added | Russell McMahon♦ | timeline score: 1 | |
| Feb 20, 2020 at 10:20 | comment | added | Bimpelrekkie | higher hFE (1200mA, as compared to 400-800mA in the non-h version). hFE (or \$\beta\$, the current amplification) isn't expressed in mA. It has no unit since it is a ratio of currents. The lower hFE should not matter, if it does then the designer was asking for trouble as hFE isn't a tightly controlled value, it can be very different on the next transistor of the same type. So a good design will work even with a much smaller (or larger) hFE. You have the schematic and there are voltages indicated so measure them. A significantly different voltage indicates broken components. | |
| Feb 20, 2020 at 9:56 | history | asked | UpTheCreek | CC BY-SA 4.0 |