Theoretically, it shouldn't matter whether the rectifiers are fast-recovery
or not for a 120 Hz application; however, diodes in a series string will
handle transients much better if their recovery times are all the same
(regardless of fast, or slow). The reason for this is, while the
low-frequency signal will divide amongst the diodes in the series string
according to the reverse leakage currents (assuming no diode in the string
ever avalanches, or breaks down), the high-frequency signal such as a fast
transient will divide instead according to trr (reverse recovery time) and
Cj (junction capacitance). The rectifier string appears as a string of
capacitors, not semiconductors, to a fast transient.
WB2WIK/6
"Each success only buys an admission ticket to a more difficult problem." --
Henry Kissinger
> -----Original Message-----
> From: EVonvaltie@aol.com [SMTP:EVonvaltie@aol.com]
> Sent: Friday, May 03, 2002 12:31 PM
> To: amps@contesting.com
> Subject: Re: [Amps] P600M diodes in HT supplies
>
> What reasoning leads you to believe that these diodes (fast recovery) do
> or
> don't need 'equalizing' R's or C's any more or less than standard recovery
>
> diodes.
>
> I have always been skeptical of this anyway. I think it originated back in
>
> the early days of Si diodes when things were several generations back in
> semiconductor design. In particular, the early diodes had horrendously
> high
> leakage compared to todays, enough to guarantee more than a few ua. of
> Ireverse at full PIV.
>
> I have the two following facts (not opinions, please note) to offer:
>
> 1. I have not bothered with R/C equalization for over 20 years
>
> 2. I have not blown a rectifier for over 20 years, even during some
>
> serious condx
> of short or low-R on B+ line. I have used strings of 4007's and
>
> 5408's in
> supplies up to 4 or 5 KV.
>
> If we are going to still cling to this old bit of folk lore, let's see
> someone formulate a cogent argument in support thereof. Let the hand
> wavers
> go work on cross-field antenna design.
>
> Eric von Valtier K8LV
>
>
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