[Amps] Caps,snubber, mov across diodes ?

[Gary Schafer]

Hi Jim,

Some time ago I built a homebrew receiver with a transformer that had too
high a voltage for the circuit. So I put a choke between the diode
rectifiers and the filter caps (choke input). I chased noise in the receiver
for a long time until I put a small capacitor (.01 or so?) from the choke
input to ground. It completely killed the diode switching noise in the
receiver and the choke still did its job of holding down the voltage in the
circuit.

Generally I have seen it discouraged to put capacitors across diodes because
of the large tolerances in those bypass caps. If the diodes are run close to
their limit having capacitors of different values could cause some
unbalanced division of transient voltages to be present on some diodes.

73
Gary  KEF 

> -----Original Message-----
> From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of 
> Jim Thomson
> Sent: Sunday, July 26, 2020 11:48 AM
> To: amps at contesting.com
> Subject: [Amps] Caps,snubber, mov across diodes ?
> 
> Date: Sat, 25 Jul 2020 23:42:54 -0700
> From: "Jim Thomson" <jim.thom at telus.net>
> To: <amps at contesting.com>
> Subject: [Amps] Caps,snubber,  mov  across  diodes ?
> 
> ##  I found this on wickipedia, under ..diode bridge.  Im 
> guessing the leakage inductance and parasitic capacitance 
> they refer to... will change depending if the plate xfmr is  
> a step down..or step up type.
> Big difference between a 10 vac sec...and a 2000 vac sec.
> 
> ##  How do I look for these..oscillations ?  I do have a 
> battery operated  fluke scope meter..and a fluke dvm..and 
> also hv probe.   Where do I measure ?   Across each 
> diode...or  B+  to  B-..... or B+  to chassis, or
> some place else ? 
> 
> Jim  VE7RF
> 
> 
> Snubber circuits[edit]
> Power-supply transformers have leakage inductance and 
> parasitic capacitance. When the diodes in a bridge rectifier 
> switch OFF, these "non-ideal" elements form a resonant 
> circuit, which can oscillate at high frequency. This 
> high-frequency oscillation can then couple into the rest of 
> the circuitry. Snubber circuits are used in an attempt to 
> mitigate this problem. A snubber circuit consists of either a 
> very small capacitor or series capacitor and resistor across a diode.
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