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Center tap vs single tap w/ bridge

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jasonc2

jasonc2

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In power supply design is there ever an advantage of a single tap transformer w/ bridge rectifier over a center tap transformer with a two-diode rectifier? It seems the single tapped designs have the same power output but always have more voltage drop across the rectifier?
 

Yes. The secondary windings of the center-tap transformer must be designed for the 1.4-fold VA due to the higher rms to average current ratio, in other words, it has -17 % rated power. At low output voltages, the effect is partly compensated by lower rectifier losses.
 
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    jasonc2

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Yes, the bridge rectifier has two diode drops and the center-tap full-wave circuit has one diode drop. But the center tap uses the transformer less efficiently since only half the wind is conducting at a time. That generally means a larger transformer for a given power output.

One interesting option for the center-tap design is that you can use two sets of diodes, one to generate a positive voltage, and one set to generate a negative voltage, handy if you need a plus and minus supply. A bridge rectifier can be used to provide the two sets of diodes by just grounding the center-tap and connecting the bridge to the two winding outputs.
 
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Thanks. So... then, aside from a mysterious global shortage of single tap transformers, is there ever a reason to use a center tapped design if you didn't need +/- voltage outputs?
 
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aside from a mysterious global shortage of single tap transformers
Click to expand...

Transformers are often provided with a center tap, just in case you want to use it, but they are perfectly happy operating as a single-tap transformer (by simply leaving the center tap disconnected).

is there ever a reason to use a center tapped design if you didn't need +/- voltage outputs?
Click to expand...

This isn't directly related to your situation, but center-tapped transformers are useful for push-pull converters, which are nice for high power but inexpensive DC/DC conversion; **broken link removed** for a comparison of isolated DC/DC topologies.
 
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