Powering a device with Ac and Dc

[xenobie]

Dear Friends,

I am building a device which requires 12VDC however it can either be powered by a car battery which is already 12V OR by 12VAC (or maybe 16VAC)

At first I thought it was simple because I can simply put a bridge rectifier and a 7812 and AC or DC won't effect my electronics. But now I am thinking about the voltage drop of the 7812 and the diodes. As far as I know, the 7812 needs at least 1.2V more in order to be able to regulate the voltage. So when using AC, there is no problem ... but with the car battery ... im clueless!!

Thanks
X

[xenobie]

 

[Hero999]

You may get more help if you provided more information, such as what the device actually is?

You could put ORing diodes after the regulator and if you're cleaver you can configure it so it only looses a diode drop when running off the battery.

Oh and the LM7812 needs between 2V to 3V to regulate properly, 1.2V is much too low.

[vera]