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Old 31st July 2011, 07:51 AM   #1
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Location: Electrostal, Moscow region
Default PA-100 oscilate with SMPS

Hi! I have found strange behavior PA-100 when i try use SMPS180QR (connexelectronic) instead of the usual PS with 50Hz transformer.
What i mesure? I mesure idle, with no load and short input, when connect usual PS, 110mA chips no heat
With SMPS i mesure 370mA and chips overheating, oscillating
I use 0.1% tolerance resistors in feedback, and 3% in out. I mesure DC offset, -2mV of each chip.

I have that problem on one channel, second channel with second SMPS180QR work well. Is this a problem of SMPS?
Some progress, i try to use second SMPS and problem not solved, i think it is not problem of SMPS
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Last edited by Professor; 31st July 2011 at 08:07 AM.
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Old 1st August 2011, 06:48 PM   #2
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Is that schematic complete? Then the decoupling capacitors for the second LM are missing. It would be better to use two Zobel networks between the amps and the load sharing resistors instead of a single one after the resistors. It could also help to experiment with those 5 pF capacitors in the feedback loop. First try to omit them. If that does not help, try to increase their value and/or put a resistor in series with them.

If you only have that problem on one channel, then you should also look where the difference lies.
If you've always done it like that, then it's probably wrong. (Henry Ford)
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Old 2nd August 2011, 05:57 PM   #3
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Hi! I make a mistake when i making PCB. 50Hz power supply forgives small errors as for example crossing by components of power lines and etc. But if you want use SMPS it is necessary to consider rules of configuration of high-frequency devices.
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