Making CT transformers from two transformers

infernal · 14th July 2011, 08:19 AM

Is it posible to make center taped transformers from two "regular" ones by connecting lead out of phase with respect to each other?
Do I need two rectifiers? Can I connect both - from rectifier to same ground?
Thanx in advance

Elvee · 14th July 2011, 08:42 AM

In theory you could.

But there are some potential problems.

The main one is that the transformers will be subjected to DC bias.
When both windings share the same core, the flux it sees averages to zero. it is not anymore the case with separate transformers.
Even if you use two sets of rectifiers to build a symetrical supply, any imbalance in the + and - currents will cause DC bias.

Another problem is that you will under-utilize the transformers: the copper is only used half of the time.
CT transformers take this fact into account and have a reduced copper area compared to the primary, but with separate transformers, you'll have to derate the output current by ~30%.

In summary, it is better to use a rectifier bridge and parallel the secondaries.
There will be one more diode drop, but in general that's negligible.

14th July 2011, 08:19 AM	#1
infernal diyAudio Member Join Date: Nov 2010 Location: Banja Luka	Making CT transformers from two transformers Is it posible to make center taped transformers from two "regular" ones by connecting lead out of phase with respect to each other? Do I need two rectifiers? Can I connect both - from rectifier to same ground? Thanx in advance

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14th July 2011, 08:42 AM	#2
Elvee diyAudio Member Join Date: Sep 2006	In theory you could. But there are some potential problems. The main one is that the transformers will be subjected to DC bias. When both windings share the same core, the flux it sees averages to zero. it is not anymore the case with separate transformers. Even if you use two sets of rectifiers to build a symetrical supply, any imbalance in the + and - currents will cause DC bias. Another problem is that you will under-utilize the transformers: the copper is only used half of the time. CT transformers take this fact into account and have a reduced copper area compared to the primary, but with separate transformers, you'll have to derate the output current by ~30%. In summary, it is better to use a rectifier bridge and parallel the secondaries. There will be one more diode drop, but in general that's negligible.