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Old 6th June 2003, 03:16 PM   #21
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You can use 2 bridges with a CT transformer but you dont get the benefits that come with using 2 bridges and a transformer with dual secondaries.
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Old 6th June 2003, 06:18 PM   #22
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Quote:
Originally posted by AudioFreak
You can use 2 bridges with a CT transformer but you dont get the benefits that come with using 2 bridges and a transformer with dual secondaries.
A CT transformer is also a dual secondary one... if you separate the central wires.

Sometimes it's an easy thing to do: you just take the plastic cover and simply cut the central wires. Of course you will have to locate which wire belongs to which phase.

Sometimes they use a single wire that is connected to the mid point, so then you will have to locate that point, eliminate the single wire, unwind the central point and cut the wires. Though it may happen that that point is deep in the winding. No deal then.

If you separate phases and wire all bridges in the same way, I don't see why you can't use four bridges with two secondaries.


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Old 6th June 2003, 06:47 PM   #23
pooge is offline pooge  United States
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I'll have to be more specific with the schematic in the Grodinski patent I cited above. He shows two secondaries, both of which are center-tapped. On one secondary, he has a diode connected to each winding end pointing to the positive rail, and the center tap is grounded. As to the other secondary, he has two diodes connected to the negative rail, with each diode pointing to opposite ends of the winding, respectively. Like the other secondary, the center tap is grounded.

I initially judged this sceme as a 2-diode full-wave equivalent to a separate full-wave bridge on each secondary. It may very well be equivalent, but I don't have the time right now to analyse it more fully. It's been a while since I've looked at this kind of stuff.

The crux of the patent, however, is in applying damping resistors all over the place to damp resonances, or energy storage due to "shock exitations", as he calls them. The resistors are applied acoss every transformer winding, PS cap, regulator output, etc. The resistors across transformer windings are selected to draw from 1 to 5 milliamps. He was less specific with the resistors across the caps, stating that they may be between 5K to 100K. In a sense, they are like bleeder resistors, only higher value.

Maybe he was snubbing diodes in the rectifier, and didn't realize it. However, such resistors across windings, PS caps, and regulator outputs can force the PS voltages to be equal amplitude w/r/t ground via their voltage divider function. Placing these resistors close to the tranformer and PS caps can keep the resulting ground current from maintaining equal + and - voltages closer to the transformer, and away from signal grounds, board PS grounds, and star grounds.
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Old 6th June 2003, 09:13 PM   #24
pooge is offline pooge  United States
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Raka, what diodes did you use, especially the PIV values?
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Old 28th July 2012, 12:54 PM   #25
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In a desperate attempt to save some space I am wondering if I can run 2 bridges off one winding (more accurately, 2 windings series connected), one providing a positive supply and the other a negative one. Is this reasonable, assuming that I respect the VA rating of the transformer?
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Old 28th July 2012, 06:47 PM   #26
mikelm is offline mikelm  England
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what say is not specific enough to be clear - best to draw what you had in mind.

your question may be answered when attempt to draw your proposed scheme.
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Old 29th July 2012, 02:53 PM   #27
piano3 is offline piano3  United Kingdom
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Thank you; actually I was just asking whether it was reasonable to run several bridges from the same winding; it is not something I have seen done so I assume that there must be some disadvantages/ caveats. I have solved my problem another way.
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