Determining zener diode voltage?

[algorithm]

A good while ago I removed a lot of components on a board to clean it. Months later I got around to trying to finish-repopulate the board, and realized I did not take notice of the identity of 3 zener diodes.

They are each a different size. I know what voltage they should be. I just have no idea about the 3 loose zeners now that they are off the board.

Is there ANY way to figure out what voltage rating these are without building a test circuit?

1 thing I should mention is that each zener is a different size, like the 3 brown bears from Goldie locks. Could the voltage value correlate with size?

Thanks for any advice.

[Andy Watson]

Is there ANY way to figure out what voltage rating these are without building a test circuit?

How difficult will it be to build a circuit of series resistor to supply 5-10mA through the zener  and then measure the voltage?

Could the voltage value correlate with size?

No. Although you might get some hint by considering their power dissipation.

Are there no markings on the zeners?

[ivaylo]

If you have a PSU with these controls, limit the current to 10mA or so and do a manual voltage sweep with the zener properly connected. Then watch at what voltage the PSU hits the current limit you put...

[T3sl4co1l]

Set the power supply to a high enough voltage and connect it to the zener through a large resistor (like 10k or 100k).

Definitely don't connect the zener directly to a bench supply with any more than zero volts on its output.  There's a beefy capacitor on all of these, and even if you set it for 10mA current limit (or whatever), it ain't gonna be 10mA for the several miliseconds before the power supply actually responds!  Bringing it up slowly (precisely as ivaylo says) should be okay.

Also works on neon bulbs, GDTs (vary supply to find breakover, sustain) and MOVs.  Assuming you have the hundred(s) of volts to spare, that is.

Tim

[algorithm]

Are there no markings on the zeners?

Thank you for this, after holding the zener up to my face for a close inspection, there is something printed on them... Not quite sure how to decipher them though...

1 says
C1
N7
49

the other says

SC
6VS

My guess is 4.3v and 6.8v? (because those are 2 of the 3 expected values)
The third one has no marking. Not really important since if I figure the 2 out there is only 1 place the 3rd can go.

Thanks again.

BTW, Im too poor and do not have a bench supply yet. Still quite a few pieces of equipment I need for diagnosing problems..

[c4757p]

Surely you have something that makes voltage? 9V battery?

[ivan747]

The 1N749 is the 4.3V Zener. Look:

http://www.mouser.do/Search/m_Search.aspx?Keyword=1N749

[algorithm]

Surely you have something that makes voltage? 9V battery?

Yeah, I have lots of things that make voltage. Have a big box of old varying wall warts... I do not have any 9v batteries though.

[algorithm]

The 1N749 is the 4.3V Zener. Look:

http://www.mouser.do/Search/m_Search.aspx?Keyword=1N749

Perfect, thank you.

[Zero999]

Surely you have something that makes voltage? 9V battery?

Yeah, I have lots of things that make voltage. Have a big box of old varying wall warts... I do not have any 9v batteries though.

A wall wart and 10k resistor would do. If the zener is forward biased, it'll read about 0.7V, when reverse biased, it'll read the zener voltage, providing the power supply voltage is high enough.

[madires]

... or build a Transistortester (see https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/ ) with the zener option Based on the DC-DC boost converter used you can check zeners up to 50V.