Standard vs Fast Recovery Bridge Rectifier

[forrestc]

I'm repairing a piece of test equipment (HP E4351B), which has a shorted bridge rectifier.

The one which is in here is a CRB35F-040P.  The 'F' means fast recovery.   This particular part has been discontinued, but I can get numerous versions of the same part with "standard recovery" diodes.   

Since this is a 60Hz power supply (the bridge is connected directly to a non-center-tapped ~120VAC secondary on the main transformer), I'm not sure why one would spec a Fast Recovery rectifier in this application.   Especially since it seems to be fairly well filtered with ~3600uF of caps on the DC side.

My current plan is to just replace it with a mechanically-identical standard recovery bridge rectifier with at least as good of specs as this one.  But before I do, I figured I'd ask to see if there was some esoteric electronic reason why this might be specified the way it is.   

[tautech]

Yeah seems weird that fast recovery was used in a linear supply, aren't they noisier ? 

Yeah I'd be replacing it with an ordinary bridge too.

[floobydust]

I find a fast-recovery rectifier is more important for higher voltages, as slow diode recovery makes more switching noise.

Bridge D709, HP 1906-0383 is Taitron RKBPC35-04 35A 400PIV 150nsec trr
Vanilla KBPC35 I could not find trr, so who knows if it makes a big difference.

Agilent  E4350B and E4351B Solar Array Simulators Service Manual Addendum A

[forrestc]

D

I find a fast-recovery rectifier is more important for higher voltages, as slow diode recovery makes more switching noise.

Bridge D709, HP 1906-0383 is Taitron RKBPC35-04 35A 400PIV 150nsec trr
Vanilla KBPC35 I could not find trr, so who knows if it makes a big difference.

Agilent  E4350B and E4351B Solar Array Simulators Service Manual Addendum A

Darn, I missed that document, it's even on the Agilent Website.....   Saving for later

And RKBC35-04 Seems discontinued as well...

[David Hess]

Some standard recovery rectifiers suffer from excessive switching noise.  If this is an issue, then fast recovery rectifiers can be used or snubbers can be added to the standard recovery rectifiers.

[floobydust]

I see Agilent/HP has a 0.1uF cap across the transformer secondary, all I find that does is lower the ringing frequency, it's undamped.
Better than nothing if slow diodes are used.

[forrestc]

Well, hopefully I've found a replacement fast diode bridge.... Should be here in a few days.

It's interesting that noone makes these anymore even though they generally should be the better solution.

[David Hess]

Tektronix usually did the same thing with a 0.1 microfarad capacitor across the transformer secondary.  Some designs place from 220 to 1000 picofarads across each diode which I find works better.