12v ac to 12v dc

[Dave Senior]

Hello,

I have a 12vac power supply and want to know if it is possible to build a rectifier to convert it to 12vdc. I'm thinking of something on the lines of the KEL84 bridge rectifier/diode upgrade. This is to power a Cambridge Dacmagic plus.

Thanks
Dave

[bob orbell]

Hi Dave, you can, but the output will be less because of the .7 volt loss of the diode, you need a full wave bridge and smothing capacitor, you may also need a ragulator, so a transrormer of 18 to 20 volts would be needed.

[Richard]

Hi Dave,

It will depend on the size of your 12V TX. When bridge rectified you should get a minimum of 15V and always a little more if you use schottkies due to the less forward voltage drop as Bob mentions.

Used passively like that the final V out will then be set by the load - how much it drags down the voltage. Ripple will also depend on the load.

What I'd do is rectify your 12V then use a LDO (low drop out) regulator. Get an LM1084 12V. The data sheet
http://www.ti.com/lit/ds/symlink/lm1084.pdf
has the simple working drawings if you've not used them before. These are 5A and will work with just 1.5V over-voltage. So long as your rectified TX output isn't dragged down below that you will end up with a good regulated supply. If it is dragged down check current drawn with a meter and change the TX to a bigger one.

[Dave Senior]

Thanks for the advice chaps

Dave