Automotive 12V to +-20V converter

[audioguru2]

It is not a bridge rectifier. I was wrong. But the coil is playing a weird part in this. Follow the polarity.

Of course it is a full-wave bridge rectifier and with the seconday's center-tap grounded, produces positive and negative voltage outputs.
L1 connects the center-tap to ground and doesn't have any current through it when the positive and negative load currents are equal. ;D

 

[Kevin Weddle]

Audioguru, read my last reply. It will explain it. It's the polarity of the coil. Trust me. If your looking for the positive supply, the polarity of the coil remains the same for both cycles. But if your looking for the negative supply, the polarity of the coil remains the same for both cycles, but it is opposite the positive supply.

I have determined this not to be a standard bridge. The problem with the circuit is the coil location. Thank you.

 

[audioguru2]

Kevin,
Coil L1 is just a piece of wire to ground, with a small inductance to slow-down  the fast charging current of the filter capacitors when the positive and negative loads are unbalanced. Since the center-tap is grounded, when one end of the secondary is positive, the other end is negative and they keep swinging with opposite voltages.

The secondary rectifier bridge is a standard circuit for a dual-polarity full-wave output.

 

[Kevin Weddle]

Can you see the polarity problem I am talking about? Just scribble it down on paper. The polarity of the coil for the positive supply is opposite for the negative supply.

I am very skeptical about this situation. If it does not work on paper, there is something screwy going on.

 

[audioguru2]

The polarity of the coil for the positive supply is opposite for the negative supply.

It doesn't matter because the resistance and impedance of the coil L1 is very low. The current comes from the entire secondary winding, not from only half of it. Since one end of the secondary is positive and the other end is equally negative, the center-tap is at ground voltage.

The center-tap is connected to ground through the coil as its 0V reference. If it wasn't connected to ground, the power supply would still work, but its output voltages would drift all over the place while still 40V apart. +20V might drift up to +30V, while -20V would drift up to -10V.