On Thu, 15 Sep 2011 15:37:23 -0700, "Robbie Hatley"
put finger to keyboard and composed:

At least 2 of these motor drive boards (one from Advanced Drive
Technology, one from Hyundai) also have switching power supply
circuits for generating low voltages needed (+5V, +12V, -8V, etc),
and these circuits all use a transistor switching a transformer,
with a feedback circuit using a P181 optocoupler and an unknown
device (dual zener?) labeled just "3B". The "3B" device is
designated "ZD3", so I'm assuming it's a dual zener diode, but
I haven't been able to identify it. It looks like this:

http://www.well.com/~lonewolf/3B.jpg

It's surface-mount, with the tab and all 3 pins soldered to the board.
Pin 2 and the tab are connected together internally, and connect to
ground externally.

With my meter set to "Diode", i'm seeing a diode from p1 to p3
and a diode from p2 to p3. The reading between p1 and p2 is
indeterminant.

Anyone have an idea of what this part is?

If you hadn't identified the component as a dual zener, I would have
guessed that it was a PNP transistor with an ECB (123) pinout.

In fact I can't recall seeing a dual diode package where the tab
wasn't either the common anode or common cathode. But then my memory
isn't the best anymore ...

Can you help us out with a little circuit tracing? The circuitry in
that area is typically very simple. In fact, we may be able to work
out the zener voltage(s) by knowing the output voltage of the supply
plus the values of any feedback resistors in potential dividers, etc.

Could we see a close-up photo?

- Franc Zabkar
--
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