# Power supply transformer size differences, linear

Discussion in 'The Projects Forum' started by smokingwheels, Aug 20, 2011.

1. ### smokingwheels Thread Starter New Member

Aug 20, 2011
4
1
I can remember from my training some 20 years ago that the transform size in a power supply depends on the configuration.
A certain size one for a full wave rectifier no center tap.

The question is can you reduce the transformer size if its a half wave center tapped ?

I seem to remember something about each half of the transformer supplying the current half of the time.

I just wanted to know if this is true?

2. ### Hi-Z Member

Jul 31, 2011
157
17
Without knowing definitively, I should doubt there's any difference in transformer size whether you have conduction in a single secondary 100% of the time or have 2 secondaries which each conduct 50%. Actually, the additional bulk of the 2nd secondary will probably mean that, everything being equal, the transformer ends up being larger.

I suppose there is an advantage in having a centre-tapped secondary, though: you save 2 rectifier diodes.

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3. ### #12 Expert

Nov 30, 2010
16,689
7,329
FWCT: Transformer secondary current must be rated at 1.2 times the DC current.
FWB: Transformer secondary must be rated at 1.8 times the DC current, but the voltage is about half, so the wattage is less than what would be needed for a 2 diode FWCT.

For instance, a FWCT transformer might have 24 volts end to end. Rated at 1 amp, the transformer can produce .833 amps at 17 volts minus one diode loss.

A full wave bridge transformer rated at 12 volts, 1.5 amps, can produce .833 amps at 17V minus 2 diode losses. This 18 watt transformer produces the same current as the 24 watt FWCT transformer and misses the same voltage by one diode drop.

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