Fast recovery bridge question

**texaslonghorn** · 15th November 2009 05:11 PM

I am thinking about replacing the basic KBPC 1002 rectifier bridge (200v rev, 140v RMS max, 10A fwd, 1.2v fwd drop) in my amp with a fast, superfast or ultrafast bridge. I am having a hard time finding one with similar specs. My question is this - just ahead of the bridges are 5A fuses, so can I use a bridge that is 6A or 8A rather than 10A? Am I correct that with that rated fuse, the bridge won't see anything more than 5A to begin with? Any other thoughts on this subject are appreciated as well.

**Sceadwian** · 15th November 2009 05:18 PM

Why are you replacing the bridge? Standard power diodes work at AC mains frequency 100% perfectly and even quiet a bit beyond that frequency, you will gain absolutely no performance using a fast diode. Unless someone else can think of a reason why a fast diode might be useful at 50/60hz

**mneary** · 15th November 2009 05:39 PM

Originally Posted by Sceadwian

Unless someone else can think of a reason why a fast diode might be useful at 50/60hz

An ordinary bridge rectifier doesn't let the snake oil flow freely enough.

**Sceadwian** · 15th November 2009 05:46 PM

heheh nice one neary.

Forgive the little jokes Texas, but anything you have read that says a fast rectifier diode will provide better performance for a power rectification application was straight up dead wrong. Please don't post anything you've read, I don't care what the sources are, they were wrong =) IF this is for other than a 50/60hz power rectifier you may actually have a reason for changing diode types, but otherwise you do not.

The more I think about it the worse an idea I think it is as well. Because a fast rectifier diode will actually increase the transfer of transient spikes, as one of the primary things that limits a diodes switching speed is it's internal capacitance. Using fast diodes might actually increase noise coupling from those types of sources.

**texaslonghorn** · 15th November 2009 05:56 PM

Ok - I see now. I am self-taught in electronics so I am learning - I don't argue with anyone here - but I do ask questions for my complete understanding. Generally, I learn by trying something I read about - then I watch as my work (and $$) begins to smoke or as I go through fuse after fuse.... So thanks for the comments - it does make sense as I think about it.

One amusing thought - I am a member of a couple DIY audio forums and what I find interesting and quite funny at times is the divergence of views between audio geeks and non-audio EE's about the performance and usefulness of various mods, parts, etc. I tend to post my questions here and on the audio forums and try to find what makes the most sense to me, then go in that direction. Sometimes, I find it beneficial for me to be stupid.

**Sceadwian** · 15th November 2009 06:43 PM

Don't worry we don't want to argue either =) But I can think of absolutely no reason why using a high speed diode would be an advantage on mains powered AC. If you can provide even a clue as to why you would want to do this in the first place or where you heard that using high speed diodes would be beneficial it might helps us educate you better. Don't be fooled into thinking high speed somehow means the diodes are better for your application. At 50/60hz the type of diode you use is virtually irrelevant, a high speed diode wouldn't offer any advantages I can think of until you get into multiple khz. Just because an audio device operates at multiple kilohertz does NOT mean that using high speed diodes on the main bridge would be of benefit, the filter caps are more important that the bridge is at that point.

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