Determining zener diode voltage? - Page 1
Forum section: electronics / beginners

author: algorithm
author_rank: Regular Contributor
timestamp: November 15, 2014, 11:22:59 pm
content: 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.

author: Andy Watson
author_rank: Super Contributor
timestamp: November 15, 2014, 11:31:50 pm
content: Quote from: algorithm on November 15, 2014, 11:22:59 pmHow difficult will it be to build a circuit of series resistor to supply 5-10mA through the zener and then measure the voltage?QuoteNo. Although you might get some hint by considering their power dissipation.Are there no markings on the zeners?

author: ivaylo
author_rank: Frequent Contributor
timestamp: November 16, 2014, 07:48:48 am
content: 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...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 16, 2014, 08:22:50 am
content: 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

author: algorithm
author_rank: Regular Contributor
timestamp: November 21, 2014, 12:25:44 am
content: Quote from: Andy Watson on November 15, 2014, 11:31:50 pmThank 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 saysC1N749the other saysSC6VSMy 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..

author: c4757p
author_rank: Super Contributor
timestamp: November 21, 2014, 12:33:42 am
content: Surely you havesomethingthat makes voltage? 9V battery?

author: ivan747
author_rank: Super Contributor
timestamp: November 21, 2014, 12:48:14 am
content: The 1N749 is the 4.3V Zener. Look:http://www.mouser.do/Search/m_Search.aspx?Keyword=1N749

author: algorithm
author_rank: Regular Contributor
timestamp: November 21, 2014, 12:52:23 am
content: Quote from: c4757p on November 21, 2014, 12:33:42 amYeah, 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.

author: algorithm
author_rank: Regular Contributor
timestamp: November 21, 2014, 12:57:27 am
content: Quote from: ivan747 on November 21, 2014, 12:48:14 amPerfect, thank you.

author: Zero999
author_rank: Super Contributor
timestamp: November 21, 2014, 01:14:45 pm
content: Quote from: algorithm on November 21, 2014, 12:52:23 amA 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.

author: madires
author_rank: Super Contributor
timestamp: November 21, 2014, 02:09:50 pm
content: ... or build a Transistortester (seehttps://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/) with the zener optionBased on the DC-DC boost converter used you can check zeners up to 50V.