[SteveC68]

I was doing a web search for power supply schematics and came across this website:

http://users.belgacom.net/hamradio/s...lies_on6mu.htm

I'm not sure I understand what the 4 little 100nF capacitors are doing in the bridge rectifier. Wouldn't they allow some AC to travel both ways?

Thanks,
Steve

[bunalmis]

Inductance of seconder and internal capacitor of rectifier diodes produce LC resonance circuit. 50 or 60 Hz current pulse forces to vibrates this resonance circuit.

Resonance frequency of this LC circuit near the 455Khz. This frequency is IF frequency of AM radios. Also this is modulated by line frequency therefore radio produce hum sound.

LC frequency shifts If we add the parallel capacitors to diodes and hum sound lost.

[Al_The_Man]

Wouldn't they allow some AC to travel both ways?

Thanks,
Steve

Yes actually they will, but at 50/60hz the capacitive reactance (in ohms) is high, Cap Reactance is frequency dependant, so these cap's would come into play if high frequency spikes or noise appears on the B+ line.
Also you will notice, for the same reason, there is a small cap C1 across a large electrolytic C2, this is because large Electrolytics can posses some inductance, the small cap will effectively short circuit this at high frequencies, Once you get into radio circuits , you will find that a short piece of copper wire can become an inductor at the right frequency.
Al.

[handlewanker]

Hi Steve, thanks for the link.
I built a 30 volt 2 amp power supply with variable voltage and amps from the Elektor magazine some years ago, and this one looks very interesting.

I was given a computer cpu cooling fan by a mate and I might incorporate this in my present set-up while I ponder on building a new one.

I don't really need a new one, but it's got some awesome possibilities, so I might just give it a go.
Ian.