Switching Power Supply

Thread Starter

PILOT203

Joined Sep 1, 2010
9
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.
 

Thread Starter

PILOT203

Joined Sep 1, 2010
9
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
 

SgtWookie

Joined Jul 17, 2007
22,210
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.
 

Thread Starter

PILOT203

Joined Sep 1, 2010
9
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!
 

SgtWookie

Joined Jul 17, 2007
22,210
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.
 
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