# How to test one zener diode?

#### ericgibbs

Joined Jan 29, 2010
11,553
hi 987,
Welcome to AAC.
Look at this datasheet for thr c12 st series of Zeners.
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#### Dodgydave

Joined Jun 22, 2012
9,837
C12 is a 12V zener, to test it you need a PSU of 15 to 24V and a series resistor of approx 100 to 470 ohms..

#### disturbed987

Joined May 27, 2020
9
resistor of approx 100 to 470 ohms

is 1kOhm good enough ?

#### ScottWang

Joined Aug 23, 2012
6,974
The minimum current of Zener diode should be 5mA, so you can calculate the values of resistor.

You may choose 6~10mA to calculate the values of resistor, exp pwr=15V,
R = (15V-12V)/6mA=500 Ohm
R = (15V-12V)/10mA=300 Ohm

#### disturbed987

Joined May 27, 2020
9
about the test without applied voltage i am measuring on diode testing mode or on Resistance options ?

#### ericgibbs

Joined Jan 29, 2010
11,553
hi 987.
A simple diagram, measure the voltage across the Zener, when there is current thru the zener of about 5mA.
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#### disturbed987

Joined May 27, 2020
9
i see 28.8 on 200k

and opposite on 2M(which is highest on my cheap multimeter) i see OL

#### ericgibbs

Joined Jan 29, 2010
11,553
Measure the VOLTAGE across the Zener NOT the resistance.

#### disturbed987

Joined May 27, 2020
9
i apply voltage of 16,7 v from notebook supply. 16,7-12=4.7 volts divided on 1000 ohms is 4.7 mA.

i see 5.15 when zenner is connected with the black part to the power suppy

#### ericgibbs

Joined Jan 29, 2010
11,553
i apply voltage of 16,7 v from notebook supply. 16,7-12=4.7 volts divided on 1000 ohms is 4.7 mA
hi 987,
That looks OK to me, look at this simulation of your circuit.

But where does the 5.15 come from.???
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#### disturbed987

Joined May 27, 2020
9
12.25 now

just want to analyze the measurement with ohmmeter...

#### disturbed987

Joined May 27, 2020
9
strange things are happening. I see 0.L in both directions without the zener beign in circuit.

I have put 3 new alcaline bateries in the measuring device which is Ms8217. The scale is AUTO and when connect the two probes i have 0.000

#### ericgibbs

Joined Jan 29, 2010
11,553
hi,
Inside your MS8217 when used to measure a resistance, the internal batteries apply a voltage across the component being measured.
If the component being measured is a semiconductor, the applied voltage on the test leads may forward bias or reverse bias the semiconductor, so the meter may give confusing resistance values.

BTW: Have you blown the internal Fuse of the MS8217 meter.???

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#### disturbed987

Joined May 27, 2020
9
i will measure its resistane with my mas830 C. is it an option ?

about the fuse i didnot remember. maybe yes but it should be replaced.i have my own service since maybe 7 years, but i do a lot with phones smartphones tablets and computers and i dont use the meter everyday.

i have other nickname here in forum but today i am on new notebook/my own has fault hdd/ and i dont have here my passwords.
I am the still not learned theunnameduser i think 159...

#### disturbed987

Joined May 27, 2020
9
Please answer. Are you sure that when measure semiconductors with multimeter that have AUTO in resitance the measurment can be wrong ? If i think right i have tested MOSFETs with this dmm.

In thread i gave values in 2M scale and 200K scale - from the other dmm.

#### sparky 1

Joined Nov 3, 2018
401
Sometimes we use the meter as an approximation. When more precision is needed we can order a precision voltage reference and we know it is better than the meter. It can be annoying to put together circuit and see that your best meter has error. So with zeners when it works but is'nt perfect that's ok, just takes getting used to the accuracy of of the application.
One project I used 18 volt regulator then 15V then 12V with current control and filtering for noise. The skill set comes from doing like this thread.