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Re: Which PS would you rather listen to?

194.208.88.198

Hi Dave!

What might even be more educational is to monitor the secondary voltage of the power transformer. This shows quite interesting things.

Whilst we like the advantage of the quite constant current draw of choke input supplies, your simulation shows that there is an instantaneous reversal of this current in the power transformer every cycle. Difficult to believe that this does no harm.

I always tame the spikes generated by this current reversal by a small cap before the first choke (in case of single phase supplies). I monitor the secondary voltage on the scope and size the cap such that the waveform looks like an undamaged sinus again.

This problem with choke input filters is even worse with silicon diodes. I think at the point where the current reverses there is a small amount of time in which both diodes fight against each other.

This is a bit different with three phase supplies. The current is not forced to reverse in the secondary but is handed over from one phase to the next. Still at this hand over point there is a nasty spike while the two diodes fight. While the first one does not "want to let go" the next phase's diode want's to 'take control'. In a three phase supply this can be avoided with a very small series resistor in front of the diodes of each phase. I size this resistor such that each diode cuts off a small time before the next one starts to conduct.

Best regards

Thomas

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