Curing a fizzing sound on a PSU with TL431+opto feedback
Today, I obtained two identical power supplies with TL431+optocoupler feedback and when under load, one of the power supplies was making a fizzing sound while the other one was not (both had the same output voltage and load) 
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I remembered removing a capacitor between the Reference and Cathode of a TL431 in a different model of power supply (to try to find a problem of it dropping significantly under load), which resulted in the unit fizzing.
Back to the two identical units; I increased the capacitor (which is in series with a resistor) on both units from 0.1uF to 1uF, and this fixed the fizzing problem
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A fizzing sound in a power supply (TL431+optocoupler feedback) can indicate instability and even oscillation of the TL431.
The capacitor I mentioned earlier (sometimes with a resistor in series with it) enables soft-starting and saying again, prevents oscillation of the TL431.
.I remembered removing a capacitor between the Reference and Cathode of a TL431 in a different model of power supply (to try to find a problem of it dropping significantly under load), which resulted in the unit fizzing.
Back to the two identical units; I increased the capacitor (which is in series with a resistor) on both units from 0.1uF to 1uF, and this fixed the fizzing problem
.A fizzing sound in a power supply (TL431+optocoupler feedback) can indicate instability and even oscillation of the TL431.
The capacitor I mentioned earlier (sometimes with a resistor in series with it) enables soft-starting and saying again, prevents oscillation of the TL431.
what did we say about hoarding too much stuff and depriving others of them?! *cough* socialism *cough* lol! 
