Battery Charger Circuit

Hi,

I have a xfmr that has a center tap as shown on the schematic. I hooked up two bridge diodes as shown, hoping to use the whole xfmr, which is 30V with center tap for 15V. I get 0 V on the output, can someone explain. When I use just one bridge diode using center tap, I get 14.5V.

Mark,

to answer your question "I get 0 V on the output, can someone explain?" You should be measuring the full transformer voltage. With the two bridge rectifiers wired as shown the top two and the bottom two diodes form a fullwave bridge. The four diodes connected to the transformer center tap do not conduct. They are never forward biased.

Actually the circuit connected was totally wrong. The transformer can produce 15 - 0 - 15 v txr. filnally we can make it as +15 - 0 -15v dc supply. So kingdly rearrange the circuit properly... If need more assist in this regard just contact me through my mail id

Here's all you need to do to get ~15V from this transformer. You may need to select different diodes, depending on the current requirement.

Centre-tap transformers are generally intended for circuits requiring positive and negative rails above and below ground potential, such as some amplifiers, also for for dual-voltage supplies, such as a 6V / 12V battery charger, or a supply running from 110V or 220V.

But well done for trying to obtain full-wave rectification from both sides of a centre-tap transformer ! It does seem logical to use two rectifier bridges.

Attached diagram shows my analysis of current flow in the circuit.

In your double bridge circuit, the centre-tap doesn't work because it cannot have current flowing both in and out of it at the same time.
However, I would expect the circuit output to be the full 30V (minus the diode drops).

(Ignore the -14V on fig 1, this system does not allow editing of a posted image.)