He is talking about one capacitor for each "leg" of the bridge not a
capacitor across each diode.
However you do not need any capacitors across anything when using a full
wave bridge or voltage doubler. There is always a filter capacitor across
every diode string.
With a full wave rectifier there is not always a filter capacitor across
each leg on half cycles.
Power line spikes are not going to get thru the filter capacitors and
transformer. Try measuring with a scope across a large filter capacitor with
a pulse generator and see what you get.
Capacitors or resistors across each diode can introduce unbalance in the
string unless precision components are used. Any unbalance in the string
will force higher current in a diode than there would be without any
resistors or capacitors.
With just the diodes in the string the maximum PIV will be the sum of ALL of
the diodes PIV because of the avalanche effect of each. You will not attain
that with resistors or capacitors across the diodes.
73
Gary K4FMX
> -----Original Message-----
> From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of Bill Turner
> Sent: Monday, February 08, 2016 6:26 PM
> To: Amps group
> Subject: Re: [Amps] Shunt resistors for a bridge made of 6A10 diodes
>
> ------------ ORIGINAL MESSAGE ------------(may be snipped)
>
> On Wed, 3 Feb 2016 05:35:57 -0800, Jim wrote:
>
> >## KM1H and a few others will use a single disc ceramic cap, like a
> 4700 pf @ 5/10 /15 kv variety...across each leg
> >of a FWB, so any transient will simply go through the cap...vs the
> diodes.
>
> REPLY:
>
> If you're going to do this, the capacitors should be closely matched
> for capacitance lest you introduce even more variation across the
> diodes. Capacitors will divide AC just as if they were resistors.
>
> 73, Bill W6WRT
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