28vdc to 12vdc convertor using a 7812

[bvondane]

I spent about an hour reading posts here and cant seem to find what I need...

I have 28VDC power and need two 12VDC @ < 1A outputs... I have found some simple looking schematics for using the 78xx series regulators, for example; https://www.mybitbox.com/wp-content/uploads/2009/02/circuit.jpg, however, I have not been able to find any information on how to determine what capacitors I should use...

Also, I would like to have some level of "protection" built into the device to deal with incoming and out voltage spikes (or whatever) that may damage the convertor, or the devices I am powering with it...

Any help I could get would be greatly appreciated!
-Bill

 

[Hero999]

An LM7812 should do but it will need a large heat sink as the power dissipation will be 14W, over half of the output power.

For over voltage protection try this circuit but change the 15V zener to 30V and the 18V zener to 36V.

A more efficient option would be to use a switching regulator.

 

[Wp100]

I have not been able to find any information on how to determine what capacitors I should use...

If you look at the manufacturers datasheet they give recommended cap values and circiuts.

Just in case you are thinking of connecting the two 12v outputs together to give 2amp - don't - thats a no no .

 

[jimmythefool]

Recom do some really neat switching regulators that have the usual 'IGO' format, so they can directly replace a Linear type. They're quite expensive, but if its a 1 off, and you don't want to mess about, they're worth a look

Power Conversion Products - RECOM

Jim

 

[Hero999]

You could use a Black regulator which is 90% efficient.

Official Home Page of Roman Black

If you need higher currents, it should be hard to beef up the components at bit.