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| Xantrex/Sorensen XHR 40-25 schematic? |
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| coppercone2:
how are you measuring the flickering voltage? It bothers me. But its also a SMPSU IC. I don't know if those can make voltage flicker maybe if its switching something rapidly. I think that there is a problem here, but pulse loads can do weird things. This usually means there is a bad capacitor. I assume its a linear regulator powering this IC? If you see that much AC on a filter capacitor it might mean the capacitor is bad. Of course someone that works with that chip might know for sure. 8VAC on top of a digital chip power supply rail seems like way too much Fix that because it can make other things go really screwy. Like everything on that rail is suspect if its behaving like that. Or at least verify its normal some how :-// |
| ifonlyeverything:
--- Quote from: coppercone2 on April 11, 2024, 01:50:19 am ---how are you measuring the flickering voltage? It bothers me. But its also a SMPSU IC. I don't know if those can make voltage flicker maybe if its switching something rapidly. I think that there is a problem here, but pulse loads can do weird things. This usually means there is a bad capacitor. I assume its a linear regulator powering this IC? If you see that much AC on a filter capacitor it might mean the capacitor is bad. Of course someone that works with that chip might know for sure. 8VAC on top of a digital chip power supply rail seems like way too much Fix that because it can make other things go really screwy. Like everything on that rail is suspect if its behaving like that. Or at least verify its normal some how :-// --- End quote --- I measured the 12-13V DC between pin 7 (VCC) and pin 5 (GND) of the UC3842. There's no linear regulator. The P2 connector is seeing 170V DC, which is fed through R14 to the VCC pin 7 of the UC3842. The auxiliary winding presumably takes over and feeds rectified voltage (diode CR16 and capacitor C22) to the IC, once it successfully starts up. This is all further complicated by U64 which is acting as the oscillator for the UC3842 (pin 7 of U64 to pin 4 of the UC3842)... as well as acting for the oscillator for the UC3854 PFC IC and the UC3524 full bridge IC. I barely understand how U64 works but I think it implements a startup delay in addition to acting as the oscillator... so I have no idea how there is synchronization between UC3842 pulsing on with 170V DC, the auxiliary winding taking over, and the UC3842 somehow outputting a VREF stable enough to power U64.... which then takes some time to finally generate the oscillator pulse that feeds UC3842 RT/CT inputs... which it presumably needs BEFORE the auxiliary winding can fire? :palm: Maybe I'll try probing the Q11 gate and the Q11 sense resistor, to see if the switching waveform look normal at any point, and to see if excess current (from a short somewhere) is causing the IC to repeatedly loop through overcurrent shutdown and start up. |
| coppercone2:
But you said that is 6VAC on a digital rail that goes to UC3842. it might have a wide range but VDD pins are usually DC voltages with not much AC component. Even if its just a transformer secondary thats regulated it should be smoothish I think, not 30% ripple. if I read that right 30% ripple + 1VDC out of a VDC reference regulator means there is a problem. I would start with 30% ripple being a problem |
| ifonlyeverything:
--- Quote from: coppercone2 on April 11, 2024, 11:10:33 am ---But you said that is 6VAC on a digital rail that goes to UC3842. it might have a wide range but VDD pins are usually DC voltages with not much AC component. Even if its just a transformer secondary thats regulated it should be smoothish I think, not 30% ripple. if I read that right 30% ripple + 1VDC out of a VDC reference regulator means there is a problem. I would start with 30% ripple being a problem --- End quote --- The low AC voltage I measured is across the smoothing capacitor C35 of the rectified auxiliary winding, which feeds the UC3842... as well as the PFC IC, full bridge IC, full bridge gate driver ICs, and several op amp power rails. Maybe I'll measure this with a scope as well. I initially measured it with my DMM, which refused to read anything on VDC but showed 7-8VAC at 60 hz on VAC mode. It has to be an artifact from things hiccuping and my DMM not being able to read fast enough. I have no idea why else I would be seeing 60 hz AC unless something is seriously fucked up. |
| coppercone2:
yeah, the capacitor !!! electrolytic capacitor not smoothing. news at 11 very common for caps to die and not do their job The only thing that can cause a functioning cap to do this, is if the load is way greater then what that value capacitor can do. Capacitor value in a smoothing circuit is proportional to load. More load = bigger cap to get same ripple unloaded it should be dead smooth or the diode i won't say that this is the only possible explaination, I think there might be some other possibility, but this is a VERY COMMON occurrence if its working as I described |
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