The optocoupler is broken, I can't figure out the reason, please give me some advice

alianyyj

The optocoupler is broken, I can't figure out the reason, please give me some advice [Copy link]

 

Help → The schematic diagram is as follows. I thought of using an external high voltage to drive the relay on the board. It started to work normally. After using it for a while, the optocoupler broke down. I can't figure out the reason. Please help.

alianyyj

I have deleted the wrong picture, why is it still there?

maychang

alianyyj posted on 2020-11-5 11:16 The wrong picture was clearly deleted, why is it still there?

Regardless of which diagram you use, what is your basis for judging that the optocoupler is damaged? It is not clear which component in the circuit controls the optocoupler.

chunyang

The original poster's circuit can only realize the function of power-on delay driving the relay, and there is no delay effect after a short power outage and then power on again. The circuit is too complicated and there is no need to use any optocoupler at all.

The original poster should first determine the specific phenomenon of the optocoupler damage, whether it is the LED side or the phototube side, or the problem of severe drop in current conductivity. Different damage phenomena correspond to different reasons. Judging from the circuit diagram alone, the optocoupler should not be damaged.

alianyyj

chunyang posted on 2020-11-5 15:15 The original poster's circuit can only realize the function of power-on delay driving relay, and there is no delay effect after short power off and then power on. The circuit is too complicated and there is no need to use anything...

The circuit below is built by me, just to drive the relay on someone else's board. I didn't want any delay or anything. I wanted to connect to the mains, so I used optocoupler isolation and resistor voltage reduction. I used a triode because the current provided was not enough. (I just wanted to do it as I wanted , just messing around)

The optocoupler was broken (no power was supplied, but the load light was still on

) and it was fixed after replacing the optocoupler

maychang

alianyyj posted on 2020-11-5 15:58 The circuit below is built by me to drive the relay on someone else's board. I don't want delay or anything. I want to connect to the mains, so I use optocoupler isolation and resistor drop...

"Replace the optocoupler and it will be fine"

The current amplification of your two transistors is quite large. Although there is no current in the primary of the optocoupler, there will be current in the secondary (similar to the penetration current of the transistor), which is called dark current. The relay may be activated as long as the dark current of the optocoupler you use reaches 0.2uA. If you replace it with an optocoupler with a smaller dark current, the relay will not be activated.

maychang

alianyyj posted on 2020-11-5 15:58 The circuit below is built by me to drive the relay on someone else's board. I don't want delay or anything. I want to connect to the mains, so I use optocoupler isolation and resistor drop...

A PC817 optocoupler is used to drive a relay with a working current of 20mA after amplification. The secondary current of the optocoupler is usually selected to be above 1mA, and it is best to use 2-3mA, otherwise it is easy to malfunction.

chunyang

alianyyj posted on 2020-11-5 15:58 The circuit below is built by me to drive the relay on someone else's board. I don't want any delay or anything. I want to connect to the mains, so I use optocoupler isolation and resistor drop...

In your relay drive circuit, the base of Q1 is not biased to ground, which can easily induce interference and cannot be used as a basis for judging whether the optocoupler is damaged. To drive a relay, you only need a transistor, but to drive an optocoupler, it depends on what your drive source is.

alianyyj

maychang posted on 2020-11-5 16:23 "Replace the optocoupler and it will be fine" The current amplification factor of your two transistors is quite large. There is no current in the primary of the optocoupler, but there will be current in the secondary...

The dark current is amplified and drives the relay to turn on. I think this is very likely.

alianyyj

maychang published on 2020-11-5 16:28 Use PC817 optocoupler to drive a relay with a working current of 20mA after amplification. A primary transistor is enough. The secondary current of the optocoupler is usually selected to be above 1mA, and it is best to use...

When using one transistor, the relay would sometimes make a "clicking" sound, so I added another one.

alianyyj

chunyang posted on 2020-11-5 16:37 alianyyj posted on 2020-11-5 15:58 The circuit below was built by me to drive the relay on someone else's board. I didn't want any delay or anything...

When there is only one tube, the relay cannot be attracted well. As you said, I think it is necessary to add a resistor to the base to the ground, which can also reduce the influence of the dark current mentioned by teacher Maychang.

chunyang

alianyyj posted on 2020-11-5 17:04 When there is one tube, the relay cannot be attracted well. As you said, I think it is necessary to add a resistor to the base to the ground, which can also reduce maychang teacher...

The resistance of R5 can be reduced to enhance the drive, and the drive current on the LED side of the optocoupler must also be considered, that is, the selection of R7 must also be reasonable.

alianyyj

chunyang posted on 2020-11-5 17:12 The resistance of R5 can be reduced to enhance the drive, and the drive current on the LED side of the optocoupler must also be considered, that is, the selection of R7 must also be reasonable.

I added a 1M resistor to the base of the transistor and replaced the original optocoupler. It is now normal. I kept the light on for a few days to age it and then try again.

.

chunyang

alianyyj posted on 2020-11-6 11:26 I added a 1M resistor to the base of the transistor to the ground, and replaced it with the original optocoupler. It is currently normal. I have been lighting the lamp to age it for a few days before trying again.

It is better to simplify the circuit. If the optocoupler LED side driver is low voltage, a current limiting resistor is enough. It is best to use 8050 transistor to drive the relay, and add a base current limiting resistor and a ground bias resistor.