XTRProf
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Pssst ! Got any spare capacitors ?
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Post by XTRProf on Oct 5, 2012 8:42:20 GMT
I'm not too sure about this. Can we upsize the E-Caps of SMPS without it going kaput?
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Deleted
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Post by Deleted on Oct 5, 2012 8:54:11 GMT
I'm not too sure about this. Can we upsize the E-Caps of SMPS without it going kaput? Chong I would go very carefully there.The secondary side of a SMPS is tuned. and the type of and values can be critical. The output side of any voltage regulator there is one area you can go. Replacing the main high voltage bridge rectifier diodes with faster types e.g. BYV26C, can also be of benefit. You can usually also get an improvement by soldering something like a 100nF 630V cap across the main reservoir capacitor. I actually did that to a Bush HD STB this afternoon and it is noticeably better with picture and coax SPDIF out. It also seems to be more stable with the low level DTV signals here. Alex
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Post by gommer on Oct 5, 2012 11:04:47 GMT
Huh, really? I've always thought a SMPC is a PFC (AC to 400VDC), followed by a HF switcher and transformer, then rectifier.
I've never designed one though...
Marc
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Post by Deleted on Oct 5, 2012 11:27:07 GMT
Huh, really? I've always thought a SMPC is a PFC (AC to 400VDC), followed by a HF switcher and transformer, then rectifier. I've never designed one though... Marc Hi Marc They are basically, but values after the transformer are reported to be critical. Even the obligatory high voltage capacitors between the primary and secondary sides (sometimes 2) are used for fine tuning in order to meet EMI requirements.The general consensus appears to be that you shouldn't play around in the secondary side before any VREGs. Kind Regards Alex Attachments:
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Post by gommer on Oct 5, 2012 12:11:06 GMT
Ah yes, dreaded EMC. That i can understand. I interpreted tuned as in resonant circuit, which it isn't.
EMC can be tricky indeed. OTOH, commercial EMC measures act on reducing the noise peaks to within the regulatory envelope. That's not the same as making it quiet, which is of importance for audio. But then again, messing around can give any unpredictable result, it's often a matter of black magic.
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XTRProf
Fully Modded
Pssst ! Got any spare capacitors ?
Posts: 5,689
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Post by XTRProf on Oct 6, 2012 4:25:07 GMT
I would go very carefully there.The secondary side of a SMPS is tuned. and the type of and values can be critical. The output side of any voltage regulator there is one area you can go. Replacing the main high voltage bridge rectifier diodes with faster types e.g. BYV26C, can also be of benefit. You can usually also get an improvement by soldering something like a 100nF 630V cap across the main reservoir capacitor. I actually did that to a Bush HD STB this afternoon and it is noticeably better with picture and coax SPDIF out. It also seems to be more stable with the low level DTV signals here. Noted. Between secondary winding and Vregs better play safe and use original values. Btw, as I can't find a simple block diagram on SMPS to understand it better, can I write those caps in between secondary winding and Vregs are for filtering purpose and, hence, need to be of the correct values to tune out the high frequency nasties from the Mosfet switcher?
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Post by Deleted on Oct 6, 2012 4:33:16 GMT
Chong I readily admit that I am out of my depth in that area of SMPS. As Marc remarked, that area is often regarded as a "black art" It's quite a specialised field. Perhaps Marc may be able to offer further insights using that schematic that I posted? Alex.
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