Tutorial: How to test / measure the value of a Zener / Avalanche Diode

[@jeeplvr2000]

Just saved me a ton of time trying to research a zenar diode with no markings but a gray band around it. Thank you so very much.

[@briantamburelli7573]

Thanks. Your a good teacher. You know I didn't know what the CC and the CV LEDs were on my bench power supply. I learned that and how to check Zener Diodes 😊😊😊.

[@shastrichandoo817]

Hello, thanks for this most informative video. I was able to determine that my zener that I thought was defective turned out to be good after I did the multimeter test and now the voltage test....thanks alot

[@testbenchtech]

This is a very useful video! In many applications, there is a need to “match” components. A good example of this would be in a tracking power supply. Great work again Martin.

[@mjlorton]

Very valid comment and I will cover that in the next video.

[@------country-boy-------]

Thanks mate for this video - it has been a big help. Maybe next time put an LED in series with the zener to show when it turns on. The current would need to be adjusted up to 20 or 30 mA first though.

[@Aboudy1989]

Been looking for this so long thanks

[@raycarberry1089]

Thanks for the great explanation.

[@mjlorton]

Thanks good man!

[@mjlorton]

No yet, I will do in the future.

[@mjlorton]

Thanks, good input...appreciated.

[@mjlorton]

Will post a video on the burden voltage setup in the future.

[@ElectroMac74]

hi i just get an almost new tti pl154, for 50€, and you just show me how to use it! thanks still wating for the set up for measuring a burden voltage on a multimeter! great video thanks

[@mjlorton]

Thanks.

[@J.RRandallIllinois]

Nice video, thanks. Can someone explain the difference between a zenner diode and an avalanche diode in simple terms , TIA.

[@stargazer7644]

You dont have to fiddle with the voltage. Set the supply to current limit at 10ma and leave the voltage all the way up. Connect it, and whatever the displayed voltage is, is the zener voltage.

[@monosteel]

Star Gazer Yes that is correct, not sure why he went the other method to find the Zener voltage.

[@samvlogg2713]

what if i have found the zener diode on crt tv power supply and this zener diode is short... now how do i know the value of this sir? thanks you sir and ihope you explain to me

[@Kalkaekie]

Very helpful video !

[@J4e8a16n]

This is good if you already know what kind of a diode you have.

[@carloshenrique177]

excelente video aula , PARABENS..

[@hoivien3001]

Have mjlorton ever did a review about his power source ? sorry for my english

[@coryknipe5471]

I have found a defective part on my second board based on visual things to look for that you have explained. I don't know how to identify the part. Is there a way i can send a picture to you for some help? Looks like a 1/2 black moon on one side with the markings 10 16 d. The bottom seems to be blown out. Thanks in advance

[@kgsalvage6306]

How do you test the zener diodes that have a high breakdown voltage? Some are 100v plus. Some that you tested may have been higher.

[@victorvelasquez3719]

Hey. Thanks! So, are all those Multimeters on the shelf for sale or just a collection of broken ones? lol

[@reecebower9934]

Is it safe to test 100v diodes this way? I'm recreating a guitar amp for my dad. There are two zener diodes In the circuitry because it has a built in overdrive. So my zeners have to be exactly the same because that's what produces the distortion. I also only have a 48v variable power supply so I wanna know if it's safe before I invest in something.

[@z08840]

with this method you often will get slightly different than nominal voltage - because manufacturer sets the nominal voltage for zener at specific test current which can be lower or higher than 10mA - if you take a look at VI of zener you'll find that curve of working zone is not falling strait down, but has a resistive slope

[@ΠάριςΑζής]

You are right, but we are interested in the “knee” voltage only...

[@drpsht]

You don't have to fiddle around too much with the voltage potentiometer. Once it's above the Zener voltage, it will stay mostly constant. So just ramp it up and see how it behaves - 0.0V (10mA)is a shorted diode, 0.7V(10mA) might mean forward biased, and +30V (0mA) is an open circuit Zener.

[@ΠάριςΑζής]

Correct, but for these tests you don’t need a power supply. The multimeter set in “diode” function will clear these two faults (shorted or open diode) quite easily. The constant current technique instead, is intended to verify the zener voltage, which is a qualitative test. Not a “go-no go” one.

[@philpem]

The problem is, some power supplies display the setpoint, not the voltage which is actually on the output. One of my Instek PSUs has a "DISPLAY/LIMIT" button, which switches between the terminal voltage and the set point. The other doesn't. The workaround involves a set of stackable 4mm "banana plug" test leads and a multimeter :)

[@BillyGoat4x4]

Great video, Sir, thank you. Might there be a "poor-mans" method if one can't afford an adjustable power supply? What if I ran the + lead of a battery through a Pot, can I adjust voltage and find the value of used Zeners that way? Keep up the good work!

[@Elecifun]

+BillyGoat4x4 you need to limit the current or else risk cooking the diode

[@PeterMilanovski]

The pot will just limit the amount of current, the voltage from the battery will still be there, to have adjustable voltage you would have to connect the pot across the positive and negative, in other words in parallel with the diode! The more that the pot shorts across the positive and negative the more the voltage drop across the pot and less across the diode but be sure to put a resistor in series because you don't want a lot of current across the pot or the diode...

[@coryknipe5471]

Great video but I have a problem I can not resolve. I have 5 Zener 1N4148 with 135 vdc in which there is no spec for that voltage. For a Laars Electronic pool Heater. I am thinking all 5 may be bad as they are way out of spec for that part number. The Zener is across a 12 vdc relay coil. Any ideas?

[@ΠάριςΑζής]

Something is wrong in what you say...1N4148 is not a zener diode. It’s only a low power switching diode...

[@coryknipe5471]

@@ΠάριςΑζής In all honesty, I am not an electronics guy and thanks for clarifying what I am looking at. Now that you have been kind enough to clear that up, do you check them the same way as a zener diode or is there another method you can suggest? I have power sources and necessary meters to do my checks, just need some guidance. TIA

[@ΠάριςΑζής]

@@coryknipe5471 All you need is to test them by using your multimeter set in the "diode" mode. Nothing more than that. A healthy diode conducts only in one direction in which you see in the display of your instrument its forward voltage drop, in millivolts. For ordinary silicon diodes this voltage is around 0.6 Volt, or 600 millivolt. This happens when you connect the red probe of your multimeter to the anode of the diode and the black one to the cathode of the diode. If you connect the probes in reverse, you should have no reading at all. Any reading means leaky diode, which must be replaced. If in doubt, remove one terminal from the circuit and measure it again. Also, if you measure zero or nearby at either connection, this means shorted diode. And if you measure nothing (infinity) this means open diode. These are all the possible cases you will see with diodes. Usually the cathode is marked with a silver ring if the case of the diode is black plastic, or with a black ring if the case is glass made. Some manufacturers mark the 1N4148 by the color code used for resistors. In this case you will see four rings on its body: yellow, brown, yellow, grey (that is sequentially 4, 1, 4, 8, with the last grey ring marking its cathode, having double width than the other three rings)...

[@coryknipe5471]

@@ΠάριςΑζής Perfect, thank you! you have been a great help. I have replaced all the parts on the board except the transformer which i knew how to check from past experience. That includes 3 relays, resistors and the diodes. Thanks to your video and explanation this board just needs to be sealed and its done. Identifying the diodes was my biggest issue and understanding how they work. On to the second board that it mates with. :) Thanks again

[@ΠάριςΑζής]

Cory Knipe You are welcome (but the video is not mine. I just commented in order to help you)!

[@CrisanBogdan]

Can I put a big value resistor in series with the zenner diode to measure the stable voltage across the zenner terminals? And the only thing to vary is the voltage source...

[@CrisanBogdan]

Here is a simulation result, and if you search on the datasheet you will find that the diode is 75V and 3.3 mA :) postimg.org/image/jskko2uip/

[@MrWasim100100]

nice video

[@dennisqwertyuiop]

Hello is you power supply a linear ? the Iso tech I want one i think a linear is better than switching

[@saarike]

Nice!

[@mickeygovender]

Thank you

[@jesusmurillo9712]

THANK YOU

[@philpem]

To clarify -- you put the multimeter in parallel with the PSU output.

[@philpem]

The problem with a forward limiting resistor is that the current limit will change depending on forward voltage: I = V/R So if you have a 4.7V Zener on a 10V supply with a 470R: I = (10-4.7)/470 = 11mA P = I * V = 0.011A * 4.7V = 0.053W = 53mW Which looks fine. Now increase to 15V: I = (15-4.7)/470 = 22mA P = I*V = 0.022A * 4.7V = 0.103W = 103mW And if your Zener diode is rated at less than 100mW, you just blew it up :(

[@Mohamed-jn4yr]

tks a lot 👏

[@josephianlibera9012]

i want to drop my 9-12vdc power supply to 5vdc output,. i choose to use zenner diode to step down to 6v then a LM7805 to regulate it to 5vdc..., i have a lot of diodes in my box but the problem is i dont know which one to use. can anyone tell me the code of the zenner diode i should look for? any numbers? sign? show the schematic as well..

[@ΠάριςΑζής]

You don’t need anything of these. Just feed the 7805 directly from your supply. You only need two 10μF capacitors, one at 25V at the input of the regulator and one at 16V at its output and you are done. Note: you also need a decent heat sink for this I.C, especially if you intent to draw about 1A of it...

[@b2gills]

Really once it is in constant current mode, the voltage control isn't doing anything.

[@dennisqwertyuiop]

good

[@PhilipSumesgutnerLeBirne]

Is there anything that you actually can NOT measure with the set of tools on your shelf? ;-)

[@mihkus]

You do it the hard way... You can do it with just a basic adjustable power supply, resistor, multimeter and zener that you are going to test...

[@mjlorton]

Yup...it's linear.

[@shawn2742]

How about a more realistic example....I have a zener in a circuit that has two blown resistors. I want to know if the zener that is in the circuit is still good. How do I test it? These videos are ridiculous because you can obviously test for the values of a FUNCTIONING zener. How about testing whether or not a zener IS good? And if it's not, THEN HOW do I figure out its value?

[@PelDaddy]

You start by lifting one leg to isolate the diode from the circuit. The. You use the methods here to test the diode's breakdown voltage. You compare that with the voltage in the schematic or parts list (or by looking up the part number). This tells you if your Zener is good.