"Franc Zabkar" wrote in message
...
On Tue, 13 Jun 2006 19:33:33 -0500, "g. beat" @spam protected put
finger to keyboard and composed:

This surface mount device is about the same size as other surface mount
diodes (1N4001, 1N4007) that I have dealt with.

Markings: PH-17D and cathode band

it appears to be a 17 volt Zener diode.
I have reverse engineered enough of this circuit (and a few voltages
measurements) -
to convince myself this is indeed a zener - probably 1/2 watt?

The circuit is Weller's original control board (circa 1980s) for the "EC"
series of soldering stations. Ceramic substrate and all surface mount
(not
bad for a 20 year old board - date stamped).

Anyway, this control line is "LOW" (~ 1 volt) when the Triac is ON
(soldering iron heater ON)
and goes "HIGH" (~22 volts) when Triac is OFF (soldering iron heater OFF).

This allows the LED in-line with the 24 VAC ..

LED is ON, when control line is LOW
LED is OFF, when control line is HIGH

So, this appears to be the logic they used to create LED status light for
heater activation :-)

g. beat

I suspect the "PH" is Philips. To calculate the wattage dissipated by
the zener, determine the LED current and multiply by 17V. Assuming a
current of 10mA, the wattage would be 170mW.

- Franc Zabkar
--

Thanks. I assume 20 mA for most LEDs, but that still places a 1/2 watt
variety as most likely.

Thank you !

g. beat