On Sep 15, 6:11*pm, "Arfa Daily" wrote:
"Robbie Hatley" wrote in message

...









Greeetings, group. *Lately I've been repairing motor drive boards
for variable-frequency 3-phase AC motors. *(These typically use
a diode bridge to rectify 120VAC to 160VDC, then feed the 160VDC
into a network of 6 IGBTs to generate the variable-frequency AC
to power the motor.)

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?

--
Puzzled,
Robbie Hatley
hatley [dot] software [at] gmail [dot] com

This any use, maybe ?

http://www.marsport.org.uk/smd/mainframe.htm

The section on "HP Diode Coding" looks as though it might contain some
relevant numbering to what you have ??


HP microwave diodes did not include zeners, as far as I know. Intended
for receiver applications, mixers, etc., they don't seem right for
160Vpk applications.

This manual indicates that "3B" could be either a pnp or npn
transistor:

http://elektronik.googlecode.com/fil...Catalog222.pdf
http://elektronik.googlecode.com/fil...Catalog222.pdf