Looking for Low-Current High-Efficiency Isolated Power Supply

[grieblm]

I've looked on the web and on this forum for a design for a low-current (0-25mA) 3V power supply powered from 8-30V. This supply needs to be isolated and have very low quiescent current (in the µA range would be great). Output regulation is not necessary -- I can use a linear regulator -- if necessary.

Anyone have any ideas? I know of the Maxim chip and have looked at all the Linear Tech parts already.

 

[mtwieg]

Well you'll need a SMPS and in general they aren't very efficient at low power levels. But many controllers have shutoff pins and quiescent current in the uA range. A quick look at linear tech shows the LTC1871, which has Iq of about 250uA and shutdown current of 10uA. Do you need it lower than that?

 

[grieblm]

Thanks, but none of the low-current Linear Tech power supplies are isolated. The IC you pointed out is a boost regulator -- I would need a buck mode regulator.

I didn't want to go there but I may have to design my own.

 

[mtwieg]

It can be used as a flyback controller. The only real difference between boost and flyback is that there is an isolated transformer instead of an inductor, and an isolated feedback network. Both of those are external to the controller IC, so the controller doesn't really care. In general a "flyback controller" is the same as a boost controller except its voltage feedback pin is structured differently to work with optotransistor feedback. But you can make that change with external components.

So basically, controller's aren't isolated. Isolation comes from the transformer.