Is this picture correct?

呜呼哀哉

Is this picture correct? [Copy link]

There is a picture like this, but the optocoupler is EL817, and the minimum VCEO is guaranteed to be 85V. In fact, I think this MOS tube cannot be turned off.

I don't know what everyone thinks about the Vceo breakdown voltage of the optocoupler, it is not in the manual. After the Vceo of the optocoupler breaks down, is it a low conduction voltage like a transistor?

The circuit seems ridiculous, but there are many solutions. You can connect an 85V Zener diode or TVS tube in parallel between CE to protect the optocoupler and control the switch.

maychang

When the optocoupler is turned off, the current passing through it is very small, and the voltage at both ends is relatively large. When the voltage at both ends reaches a certain level, it is "broken down". Its characteristics are roughly the same as those of a voltage regulator tube. As the current passing through it increases, the voltage at both ends increases very little. If the current is not large, the power dissipation of the optocoupler does not exceed the allowable value, and the optocoupler will not be damaged.

maychang

Assuming your optocoupler breaks down at 85V, the current through R15, R21, and R16 is (110-85)/(R15+R21+R16)=0.56mA. The optocoupler dissipates power of 85V*0.56mA=47.6mW. This value will not damage the optocoupler. The voltage across R16 is 0.56mA*3.9kΩ=2.184V. As long as the MOS tube turn-on voltage is greater than 2.184V, the circuit can work normally.

maychang

The optocoupler is marked with a withstand voltage of 85V, but in reality it may reach 100V or even higher. That will be no problem at all.

However, it is still better to use an optocoupler with a higher voltage resistance.

maychang

[I feel that the circuit is ridiculous, but there are many ways to solve it. Connect an 85V voltage-stabilizing diode or TVS tube in parallel between CE to protect the optocoupler and control the switch. ]

This method is not advisable. It is better to use an optocoupler with a higher voltage resistance.

qwqwqw2088

Is the picture correct?

To look at the entire circuit scenario comprehensively, the optocoupler is nothing more than isolation and anti-interference.

What type of load is the MOS tube?

led2015

No, if it breaks down, it will behave abnormally, stop working, and may cause an electrical short in the circuit.

lkh747566933

I have never used optocoupler to design circuits. Come and learn the circuit of the OP.

laker2008

I have never seen this kind of circuit before, I don't understand it, thank you for your answers, I will learn from it~~~

lkh747566933

The optocoupler is marked with a withstand voltage of 85V, but in reality it may reach 100V or even higher. That is no problem at all. However, it is better to use an optocoupler with a higher withstand voltage.