Zener diodes

[zpyder]

I've got a grab bag of diodes, many unlabeled.  I'd like to find a 9.1v Zener diode in there for a Mosfet Boost but I don't know how to go about finding it.  I have a DMM.

Anyone know a way to test diodes with a DMM to find a 9.1 Zener and/or some common models or common markings that I might be able to find in there?

cheers,
zpyder

[amz-fx]

You could use a 12v zener if you find one of those....

regards, Jack

[rogeryu_ph]

I 'm interested on the zener diode topic also. Sometime I do salvage some from old circuit but I can not identify which is it. 1n4148 and 1n914 or 1n916 somewhat same with Zener. Same color orange with black stripe! How to identify, test  and to know the voltage, Anyone? Appreciate very much and thanks   

[amz-fx]

Easy to measure...   connect a 1k resistor from the plus side of a 15v to 20v  power supply to the side of the zener marked with the band.  The other end of the zener goes to the negative side of the power. Use your multimeter to measure the dc voltage across the diode. Use a half-watt resistor...

Two 9v batteries in series will give you 18v which is ideal for sorting the diodes and will not overload the resistor.

regards, Jack

[zpyder]

Easy to measure...   connect a 1k resistor from the plus side of a 15v to 20v  power supply to the side of the zener marked with the band.  The other end of the zener goes to the negative side of the power. Use your multimeter to measure the dc voltage across the diode. Use a half-watt resistor...

And I'm assuming that whatever voltage I measure across the diode is the rating of the diode? IE if I read 9.1v, then it's a 9.1v?

thanks!
zpyder

[zpyder]

Easy to measure...   connect a 1k resistor from the plus side of a 15v to 20v  power supply to the side of the zener marked with the band.  The other end of the zener goes to the negative side of the power. Use your multimeter to measure the dc voltage across the diode. Use a half-watt resistor...

Could this damage diodes that are not Zener???

zpyder

[R.G.]

Zener diodes are usually specified at about 1ma of current.

However, for sorting purposes, it's fine to just measure them when they break over with a resistor between 1K and 10K on them

Yes, the nominal voltage is probably what you measure.

As a side note, *all* diodes are zener diodes, in that they will all break over at some point. What we call zener diodes are just diodes that are designed to have low breakover points and which have been pre-sorted to have predictable voltages.

The base-emitter of a garden variety NPN transistor makes a dandy zener between 5 and 7V - usually. What you get is like the proverbial box of chocolates.

[rogeryu_ph]

R.G. / Amz-fx / Zpyder and to all THANKS A LOT.....

[tungngruv]

Doesn't some of the runoffgroove projects use a 3mm red LED in place of a Zener? I'm sure I have seen that sub somewhere.

[R.G.]

Any diode may be considered to be a "zener" when it's used in the forward direction. A silicon diode used forward is a fine 0.5 to 0.6V "zener". You can stack them to get whatever you like. In the same sense, LEDs have a much bigger forward voltage, usually 1.2 to 3.0V depending on color. So they can be used as low voltage "zeners" although you're only getting the forward conduction voltage. No actually reverse breakdown "zenering" is going on.

It's hard to make zeners which break sharply and give good regulation much below 4V. So you often see strings of diodes or LEDs in the forward direction for low voltages.

You don't want to make a 30V regulator out of ten LEDs or 60 silicon diodes, though.