Split powers

[Hero999]

They protect the regulator outputs from a reverse voltage being applied to the output terminals.

 

[soundman]

Thanks, Do I need them even if there is no inductive component in the circuit?

 

[Hero999]

The diodes are there to prevent one regulator from back-feeding the other when it has shut down.

 

[soundman]

Shut down!? Why one regulator does shut down?

 

[Hero999]

A regulator will shut down if it overheats or the current rating is exceeded, for example shorting the positive to negative rail will cause the regulators to shut down. Unfortunately, one of the regulators will shut down first and without the diodes will be back fed by the one which is still working.

 

[unclejed613]

are the regulators on heat sinks??? they must be on heat sinks and mounted with heat sink grease or sil-pads. if they have metal tabs, either the 79xx regulator needs it's own heat sink, or it needs an insulating washer on the mounting screw. the tab is connected to the output pin of the regulator, and the 78xx tab is connected to ground. so if they're on the same heat sink, the 79xx needs to be electrically isolated from the heat sink, while still thermally coupled to it

 

[soundman]

Ok it makes sense now, Thanks a bunch for your helps.

 

[Reloadron]

Question;

I know your transformer says 24 Volts CT. You are sure if you measure accross the AC input to your bridge you see 48 Volts AC? If you measure from the CT to each side of the transformer you see about 24 Volts AC? I ask because on the DC side with the caps in there if the transformer is 24 Volts CT with 12 volts and 12 volts the caps would charge (unloaded) to about 16.9 VDC and measuring unloaded it should look good. But as soon as it is loaded that voltage would drop and the 12 volt regulators would be lacking the needed overhead of about 14 volts. Anyway, you are absolutely sure your transformer has 24 VAC each side of the CT and 48 VAC accross it?

Ron