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The purpose of an optocoupler is to transfer signals from one circuit to another yet keep them galvanically isolated. Here I want to show you how to check if an optocoupler is working. Step 1. If you get a value either way or no value at all, then certainly there is a problem with the LED, and you should find another optocoupler. If the LED is good then we should check the phototransistor, you could measure it with the ohmmeter just like the LED between pins 3 and 4 the emitter and collector , and you should get a high resistance value both ways if the phototransistor is good.
Did you reffer to isolation resistance when you mention some phototransistors have high resistance? I was referring to the junction resistance. If i give the input of V DC what will be the response of this optocoupler…. If the input is at 2V DC, then the output resistance should be around — ohms. For response time or frequency response data, check the datasheet. Thank you for the information… and i have one more clarifications..
I have two circuits.. 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.
Damn it. Please correct the pin numbers in image. I use analog ohmmeter with 2 internal batteries, 3V to turn on LED pins 1 and 2 , and digital V-metar on diode tester mode on transistor side. I like the way you explain things.. You helped me understand how to use a tester on a optocoupler Thanks. Just a question : i have an Arduino Relay module 2 relay and only one of the realy are working. I was wondering if i could just bypass the optcoupler and see if it works.
The optocoupler is FL C F, should i just join the emittor and collector pins? Any help would be apreciated. I hope it helps. First of all thanks for sharing such an useful information. I appriciate… I tried that emprical method for H11B1 optocoupler. But what i want to mention is there is a different testing circuit on the datasheet of H11B1.
Here is the web site. The question is which one is the right testing method? Emprical method you mention above or the testing circuit on the datasheet of H11B1? 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. 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. Pls let me know. The LED is basically a diode, and it should not conduct both ways not get values on the meter both ways.
Thx and best regards, Geert. I only have a digital multi meter. How can i test them? Plz help. Hi, The MOC, 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. 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 ohms when voltage is applied to the LED, and should remain low even if the voltage is no longer present on the LED.
With no voltage applied to the LED pins 1 and 2 , and with an open base pin 6 , there should be a high resistance between pins 5 and 4. Hi thanks for helping.
Just one question the numbers on the the optocouplers which number do i use when when trying to find replacements Thanks. Hi, search in a datasheet for your current optocoupler specs, and look for one with similar specs. Or just google replacements for your busted optocoupler :. Will this device handle a 12v input. I have a relay module incorporating DPC with a 5v Vcc applied to both pins 1 and 4, which is an odd way to wire an isolator.
Pin 1 has a series resistor. Output from here is to the relay coil. The module relay coil is 12v. The module is designed to be triggered from an Arduino at 5v but I want to be able to trigger from a 12v device.
However I do not want to fry it with overvoltage. Your email address will not be published. This site uses Akismet to reduce spam. Learn how your comment data is processed. There is no law governing all things. The alcohol never solved anything, but neither did water or milk. When Firefox stops working, you fire up Chrome. Good design is as little design as possible. The firehose by day and forty beers by night, An engineer may never sleep and still be just as bright.
The nice thing about standards is that you have so many to choose from. Step 2 If the LED is good then we should check the phototransistor, you could measure it with the ohmmeter just like the LED between pins 3 and 4 the emitter and collector , and you should get a high resistance value both ways if the phototransistor is good. Comments written by: Viliam on September 7, at am - Reply. Thank you for the information. Hi, First of all thanks for sharing such an useful information.
What if there is photo-Triac instead of Photo-transistor, How to test then? Thanks for the easy to follow explanation of how to rest an optocoupler. Thanks a lot. These information are very good indeed. Best of luck…. How the optocoupler Type SFH acts when the positive line is open. Leave a Reply Cancel reply Your email address will not be published. Search for:.