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-   -   Simple bridge rectifier question. (https://www.diyaudio.com/forums/everything-else/2279-simple-bridge-rectifier-question.html)

JoeBob 10th February 2002 05:12 PM

Simple bridge rectifier question.
 
Well, the highest rated bridge I can get is 35A and the highest load possible in my amp is 30A, now that's a little too close for comfort, so my questions is this... I'm using two 750VA transformers, two 61000 uF caps and it's a five channel amp, everything else is done except for this. Instead of running the two secondaries of the transformers in parallel and then to the rectifier then the caps could I run each transformer to it's own rectifier and then the outputs of the two rectifiers in parallel then to the caps? Or any other way to use two rectifiers so that I'm not so close to it's rated limit? Thanks alot for any replies.

audionut 10th February 2002 05:53 PM

Each transformer could have its own bridge rectifier. One transformer and bridge rectifier for the plus rail and one transformer and bridge rectifier for the negative rail. Each bridge would have less of a load.

You can go to the tnt audio sight and find a good powersupply article which talks about the merits of having separate windings/transformers and separate bridge rectifiers for each rail...also one of the recent Pass Labs threads also talks of the advantages of having two windings and two bridge rectifiers.

good luck!

Joe Berry 10th February 2002 06:09 PM

joebob,

Bridge rectifiers usually have both average and peak current ratings, where the peak rating may be around 10 times the average. So, a bridge rectifier with a 35A average current rating will probably handle 350A or so under peak conditions. If the parts catalog doesn't include both ratings, you can get a databook (or maybe download a datasheet) with full specs for the part in quesiton.

JoeBob 10th February 2002 06:32 PM

Oh, I see. I'll go check for a datasheet. I'd be alot happier if I knew it wouldn't blow up.

blmn 11th February 2002 12:49 PM

JoeBob,

When using these diodes near of their capacity you must be aware of their heatsink needs (even far from this capacity too). Please, consider the average current over them and the voltage drop (you have this information in the datasheet).

regards

paulb 11th February 2002 03:15 PM

At such high currents, another option is to use individual rectifiers instead of a bridge. Be very aware of the heatsink requirements: if you're pulling 10 amps continuously, a bridge might have to dissipate something in the neighborhood of 15 or 20 watts.
I prefer the option of splitting it up so that one transformer is for, say, the positive and one for the negative rail, or perhaps split them up by channels.

JoeBob 13th February 2002 04:58 AM

So I'd hook one transformer to the bridge and only connect the negative from that bridge, and the other transformer to another bridge with only the positive connected? Sine my transformers have two secondaries each I'd hook them up in parallel to the bridges?

subwo1 13th February 2002 05:52 AM

Or, you may be interested in hooking each secondary up to its own bridge, like you were saying at first. Then hook 2 negatives and 2 positives to ground like you said in your last post.

Jamie F 13th February 2002 02:54 PM

JoeBob

I'm using a single 35A rectifier for 10 LM3886's and it generates no appreciable heat.

Jamie

paulb 13th February 2002 03:56 PM

Quote:

Originally posted by Jamie F
I'm using a single 35A rectifier for 10 LM3886's and it generates no appreciable heat.
At full power? At 1 amp DC per channel, that bridge has got to be dissipating at least 15 watts - it should be heating up.

JoeBob, what about separate power supplies for 3 channels / 2 channels? Or is it too late?
Using just the +ve or just the -ve from a bridge is just a full-wave centre-tap connection (only two diodes are used). See the ESP article on power supplies for information on this.


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