[ARC5] Solid State --- diodes...

[Tom Lee]

Your analysis is spot on. Even "slow" rectifiers can have surprisingly 
abrupt transitions from off to on (it's a phenomenon called reverse 
recovery -- the diode stays on well after the voltage across it has 
reversed polarity; when it finally does turn off, it does so with very 
fast edges). The spectrum of the diode current looks like a remarkably 
flat comb well past MF. Shunting that RF with a cap does an effective 
job of knocking down the RFI.

Tom

-- 
Prof. Thomas H. Lee
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On 2/8/2018 3:28 PM, Kenneth G. Gordon wrote:
> I haven't seen the following issue mentioned yet, but I do remember that when using Si
> diodes in a power supply in a receiver, there appeared significant noise, i.e. RFI, from them.
>
> A constant sort of hissing or static-like interference.
>
> The way I cured this at the time was by including a 0.01 mfd bypass capactor across each
> series-connected diode, and another from each end of a bridge to ground.
>
> At the time, I attributed this RFI to the abrupt cut-off of conduction by the diode as compared
> to the slower one of a tube when the sine-wave reversed, but that was most probably wrong.
>
> Now this was a long time ago, and I haven't looked for such a thing lately, but I can't see
> that bypassing each diode with a good disk-ceramic would hurt anything.
>
> Comments?
>
> Ken W7EKB
>
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