Comments on: How to test an optocoupler

By: Sunil

Sunil — Sat, 03 Mar 2018 13:58:31 +0000

3022 optocuppler testing 1 and 2 pin get 4 v dc then out put ohms how

By: Siroos

Siroos — Sat, 14 Oct 2017 19:59:38 +0000

Thanks a lot. These information are very good indeed.

Best of luck…

By: mahdi

mahdi — Mon, 31 Jul 2017 06:55:10 +0000

thanks for your guide.

By: Mihai

Mihai — Sat, 18 Mar 2017 20:07:31 +0000

Hi,
The MOC3021, is a phototriac coupler, meaning that instead of the phototransistor, it has a phototriac, which is basically a triac with the gate driven by the LED.
The LED (pins 1 – Anode and 2 – Cathode) can be checked with an ohmmeter (or a multimeter set on a low OHM domain, or on diode test domain) as any other LED, and it should only conduct one way (as described in “Step1”).
For the triac (pins 4 and 6), with no voltage applied to the LED (pins 1, 2), check (with an ohmmeter) the resistance between pins 4 and 6, it should be high (open circuit or at least greater than 1 megohm) both ways, and this resistance should go down (lower than 500 ohms) when voltage is applied to the LED, and should remain low even if the voltage is no longer present on the LED.

By: Nupra

Nupra — Sat, 18 Mar 2017 16:44:36 +0000

Hi, I have 6 pin MOC3021 optocouplers to be used in a cct I’m working on. But it seems the there’s an issue with them. I only have a digital multi meter. How can i test them? Plz help.

By: Mihai

Mihai — Mon, 06 Feb 2017 09:14:31 +0000

No problem!

By: Wade

Wade — Sun, 05 Feb 2017 19:03:58 +0000

Thanks for the easy to follow explanation of how to rest an optocoupler.

By: Mihai

Mihai — Sun, 20 Nov 2016 11:29:45 +0000

Hi,
Connect the resistor between the “+” of the power supply and the anode of the LED.

By: Geert Van Droogenbroeck

Geert Van Droogenbroeck — Fri, 18 Nov 2016 21:10:26 +0000

Hi,

maybe a stupid question :-)
what do I connect at the resistance : + or – of the supply?
Thx and best regards,
Geert

By: Sarfaraz

Sarfaraz — Tue, 08 Nov 2016 19:15:14 +0000

Nice info

By: bablo

bablo — Fri, 28 Oct 2016 07:32:28 +0000

Thanks a lot for the useful informations.

By: Mihai

Mihai — Sat, 27 Aug 2016 19:01:47 +0000

Hi, pins 1&2 are connected to the LED. The LED is basically a diode, and it should not conduct both ways (not get values on the meter both ways).
If you are getting values both ways, it means the LED is dead, and the optocoupler it’s not working.

By: Sanu sebastian

Sanu sebastian — Fri, 19 Aug 2016 07:49:06 +0000

Hiii please help me … i have PC123 ic in pin 1& 2 am getting both side value its good or faulty ? Pls let me know

By: Shahid

Shahid — Sun, 07 Aug 2016 10:35:17 +0000

It depends on the 2nd circuit you are supplying the voltage on collector of the optocoupler, optocoupler will never transfer the voltages of circuit1 to circuit2, it decreases resistance between your supplied voltages at collector and emitter on the input of circuit2

By: Mihai

Mihai — Fri, 10 Jun 2016 09:05:55 +0000

I’ve never used a phototriac. I guess, it should work mostly the same as a normal triac. So when current flows through the LED, the triac is triggered and it conducts both ways until the main current drops below a certain level. Better check the datasheet for a test circuit.

By: Arvind Vijaykumar

Arvind Vijaykumar — Wed, 01 Jun 2016 09:57:31 +0000

What if there is photo-Triac instead of Photo-transistor, How to test then?

By: john markus

john markus — Mon, 14 Mar 2016 21:21:02 +0000

Thanks for clearity on ic 817.

By: Mihai

Mihai — Sun, 06 Mar 2016 12:07:29 +0000

Hi,
Both methods are correct. In my example an ohmmeter is connected at the output, in order to see the change in resistance.
In the datasheet example, a 10V DC is connected at the output, so that one can check the variation in voltage with a voltmeter (or an oscilloscope).

By: Barış

Barış — Wed, 02 Mar 2016 21:44:21 +0000

Hi,

First of all thanks for sharing such an useful information. I appriciate…
I tried that emprical method for H11B1 optocoupler. According to that emprical method the bjt’s are broken! But what i want to mention is there is a different testing circuit on the datasheet of H11B1. Here is the web site. http://html.alldatasheet.com/html-pdf/3038/MOTOROLA/H11B1/1036/4/H11B1.html

The question is which one is the right testing method? Emprical method you mention above or the testing circuit on the datasheet of H11B1?

By: Mihai

Mihai — Tue, 02 Feb 2016 15:54:29 +0000

Yes, you understood how the optocoupler works, and yes, the phototransistor should close the relay circuit when voltage is applied to the LED pins, and if it’s short-circuited (emittor and collector pins joined) the relay coil circuit should close.
I hope it helps.