Need suggestions on very clean 220V ac to +-12V DC(0.01mVpp ripple) design.

Dear All

We have been designing a very high precision control circuit for quite a while. And we are thinking to make it much easier to use, which is to get rid of the Lab DC Sources and use AC to DC switching power (get power from 220V/110V directly).

As we are trying to design a product which can work properly around the world, SMPS has been adopted which allows various working frequencies and voltages. However, SMPS brings much higher noises.

In our application, we need to measure current from photodiode at pA precision. Therefore, DC noises are crucial to us. Could I have suggestions on designing 0.01mV pp dc sources from wall plugs directly?

Output voltage: +12V and -12V
Output ripple: 0.01mVpp
Working current: +12V: 600mA, -12V: 300mA

Any suggestion will be highly appreciated.

Thanks a lot.

Regards

Richie

 

You need this: http://cds.linear.com/docs/en/application-note/an70.pdf

That's one of the greatest app notes ever written IMHO. It's about how to get less than 100uV pk-pk of SMPS noise. It talks about the difficulties of measuring and triggering on 100uV of noise as well.

This will get you going in the right direction. You've also asked for another 20dB of attenuation on top of what the app note talks about which will be difficult, I think.