How to make an overvoltage protection circuit?

sky999

How to make an overvoltage protection circuit? [Copy link]

 

The maximum input voltage of the board is 60V. How can I disconnect it when it exceeds 60V? I used a self-resettable fuse, but who knew that it would explode directly due to overvoltage?

maychang

The resettable fuse is used to prevent overcurrent.

Did you connect the resettable fuse in parallel across the input?

sky999

maychang posted on 2020-7-20 13:44 The resettable fuse is used to prevent overcurrent. Did the OP connect the resettable fuse in parallel at both ends of the input?

No, it's in series with the positive pole, 30VPPTC fuse, it will explode when connected to 48V

maychang

sky999 posted on 2020-7-20 14:12 No, it is connected in series to the positive pole, 30VPPTC fuse, and it will explode when connected to 48V

"30V PPTC fuse explodes when connected to 48V"

If a 30V PPTC fuse is used for 48V, it will be damaged.

sky999

maychang posted on 2020-7-20 14:16 "30V PPTC fuse, connected to 48V, it will explode" 30V PPTC fuse used for 48V, it should be damaged.

I didn't use it, I just wanted to test whether it could be used as an overvoltage protection, but it exploded as soon as I connected it.

maychang

The maximum input voltage of the board is 60V. How can I make it disconnect when it exceeds 60V?

One method is to connect a voltage regulator tube below 60V in parallel to the input end of the circuit board, and then connect a self-recovery fuse in series at the power supply. When the power supply voltage exceeds 60V, the voltage regulator tube will be broken down, the current will increase, and the self-recovery fuse will be activated.

maychang

Another method is to add a power supply voltage detection circuit, which allows the use of a relatively high power supply voltage and can withstand the highest voltage that the power supply may produce. When the detection circuit detects that the power supply voltage reaches a certain value (for example, 60V), the circuit board is disconnected (but the detection circuit is still connected to the power supply).

sky999

maychang posted on 2020-7-20 14:22 The maximum input voltage of the board is 60V. How to make it disconnect when it exceeds 60V? One way: Use a voltage regulator tube below 60V in parallel with the input of the circuit board...

Should the resettable fuse be as high voltage as possible? Otherwise, it will explode again.

sky999

maychang posted on 2020-7-20 14:29 Another way: add a power supply voltage detection circuit, which allows the use of a relatively high power supply voltage and can withstand the highest possible power supply voltage...

Um, I've thought about this, I see, thank you.

maychang

sky999 posted on 2020-7-20 14:56 Should the resettable fuse be as high as possible? Otherwise, it will explode again

The resettable fuse is essentially a thermistor with a positive temperature coefficient. When the temperature does not reach a certain value, the resistance is very small. When the temperature rises to a certain value, the resistance increases sharply. When the load is working normally, the current does not exceed the action value of the resettable fuse, the temperature of the resettable fuse is not high, and the resistance is very small, which does not affect the normal operation of the load. When the load is short-circuited, the current through the resettable fuse increases, the temperature of the resettable fuse increases, the resistance increases, and the current is limited to a relatively small value. In this state, the voltage across the resettable fuse is close to the power supply voltage, so the power dissipation is quite large and the temperature will not decrease. If the load short-circuit fault disappears, the current in the resettable fuse decreases, the temperature decreases, the resistance decreases, and the entire circuit returns to normal.

maychang

sky999 posted on 2020-7-20 14:56 Should the resettable fuse be as high as possible? Otherwise, it will explode again

Therefore, the resettable fuse has a maximum voltage that can cut off the circuit. If the power supply voltage is higher than the maximum voltage that the resettable fuse can cut off, then when a short circuit occurs, the voltage across the resettable fuse is too high, and the temperature will rise to a value that the resettable fuse cannot withstand, and the resettable fuse will explode.

sky999

maychang posted on 2020-7-20 14:22 The maximum input voltage of the board is 60V. How to make it disconnect when it exceeds 60V? One way: Use a voltage regulator tube below 60V in parallel with the input of the circuit board...

When the power comes in, the positive pole passes through the fuse first, and then the voltage-stabilizing diode is connected between the positive and negative poles, right?

sky999

maychang published on 2020-7-20 15:08 The self-resettable fuse is essentially a thermistor with a positive temperature coefficient. When the temperature does not reach a certain value, the resistance is very small. When the temperature rises to a certain value, the resistance increases sharply...

There seems to be no difference in function between a resettable fuse and a thermistor?

chunyang

sky999 posted on 2020-7-20 15:25 When the power comes in, the positive pole first passes through the fuse, and then the voltage-stabilizing diode is connected between the positive and negative poles, right?

That's right, some anti-reverse connection circuits also adopt similar practices.

chunyang

sky999 posted on 2020-7-20 15:26 So there seems to be no difference in function between a resettable fuse and a thermistor?

The curves can be very different, so you might want to look at the device manuals for the two and compare them.

sky999

chunyang posted on 2020-7-20 15:47 Yes, some anti-reverse connection circuits also adopt similar practices.

If the circuit voltage is 12~60V directly and the power is 0.1W~2W, can I use a 60V 5W Zener diode? What size should the current-limiting resistor in front be?

accon

Cascade dual pmos and voltage regulator tube

sky999

accon posted on 2020-7-21 07:13 Cascade dual pmos and voltage regulator tube

Cascade dual pmos? ? I don't understand

lkh747566933

The fuse blew, probably because the instantaneous current was too large. Use a TVS tube.