Simple bridge rectifier question.

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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.
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!
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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.

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).

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.
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?
Jamie F said:
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.
Well, I've only got 2 caps and two transformers. And if I wanted to use multple power suplies less power would go to some channels then others, which I'd rather avoid. I'll just try using a bridge for the positive and one for the negative and see how it goes. When only using either the positive or the negative poles of the bridge, the opposite pole is sent to ground, correct?
JoeBob, could you let us know what your transformer voltages are and what DC voltage you expect to get? I'm a bit confused. The arrangement you mentioned doesn't use the centre-tap of the transformer, but I was talking about using it as ground. Your way will get twice the DC voltage.

People seem to be saying that it's ok..

If you pull 30A amps out of a 35A bridge recitfier it will BURN UP. I've seen it happen many times.

Also, why don't you at least spec a 50A amp part or use individual diodes? Using individual 60A diodes you'd be fine..

-- Aaron

If you use correct sized heatsink the bridge will not blow up considering 85% of their continuous nominal capacity. I had some in my bench power supplies with this problem when I was testing some class B amps. I solved it increasing the heatsink. However, there are some manufacturers wich use peak, or not continuous, current value information for their devices as a basic information, and, in these these devices have much less continuous current capacity.

Well, I checked and the peak for my bridge is alot higher then 35A, in the hundreds, although I can't remember exactly what.

paulb, sorry, I don't really understand how you mean to connect it. Each transformer is a 750VA +/- 24VAC toroidal with dual primaries and dual secondaries. The DC voltage I'm gathering I'd get is probably around 28VDC or 30VDC, it doesn't really matter exactly, it's for some LM3886's. I hope that clarifies some things, sorry for my ignorance by the way, I just don't see how I can use one transformer for the + and one for the -, if using them the center-tapped way, wouldn't that produce twice the DC voltage, compared to using them in parallel?

i'd wire the primaries as per your mains voltage then wire the same secondaries of each transformer together and use 2 bridges to form the rails .... the + of 1 bridge goes 2 +ve rail, -ve goes to gnd, +ve of other bridge goes to gnd, -ve of same bridge goes to -ve rail.....

i'll post a pick of how this looks later if you want. you've just got to make sure all the AC phasing is correct.

Maybe something like this was the idea of PaulB. Don't worry about the polarities of the transformers.



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