Hello,

Has anyone ever seen a isolated low-power (<1watt) buck switching power supply design that uses a toroidal transformer with two capacitors, <2-3 transistor/FETs?

I took a failed 1/4 watt (3.3v output) one a part the other day and was surprised to find so few components.

 

Well, if it's isolated, then it would likely be some type of flyback converter.

Roman Black has several low-power buck and boost supplies on his site that require few components: http://romanblack.com/smps/smps.htm

 

Thanks
Here are two pictures, front and back of the regulator.
It appears to have a input and output SMD capacitors and at least three transistor or FET on the one side the board(2nd image). The first image has the two SMD's, ones a input cap on the right(fell off), the other don't know. This is also the side where the toroidal choke/transformer mounts.

The manufacturer state that its max input is 24V@10ma, 3.3v@70ma out.


http://imgur.com/rrJeJ&E430L

 

Yep, looks like in the 2nd image, the lower left transistor has a hunk blown out of it's package. The smoke has exited the transistor, and it will no longer function.

 

Surely this is the device fault! Their was no reverse voltage protection when I added to the circuit. Clearly a violation of Ohms' current law!

 

Looking at the 1st image some more, seems like something above the capacitor (the vertical brown rectangular object) got smoked.
On the 2nd image, something got blown clean off the board on the right side - might've been a diode.