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The cause of the thermistor burning out _ the role of the thermistor in the power circuit

Article source:admin Popularity:Published time:2019-10-29 17:44

How do you know that the thermistor is broken?
The multimeter selects the appropriate resistance gear. The two test leads are respectively contacted at both ends of the thermistor, and the thermistor is heated by hand or heated by other means. If the resistance changes linearly, it proves to be good, and if there is no change, it means that it has failed.

There are several reasons why the thermistor burns out:
1. The instantaneous current of the thermistor is too large, and the resistance coil is broken.
2. The resistance wire of the thermistor is insulated and protected to form a short circuit between the coils;
3. The line voltage is unstable and undulating, and the instantaneous voltage exceeds the safety index of the thermistor.
The above three points are only the cause of the general problem. The specific situation depends on various factors such as the use environment of the thermistor.

Thermistor burnout causes

What should I do if the induction cooker is damaged?
Damage to the induction cooker thermistor needs to be stopped and repaired and replaced in time.
Induction cooker thermistor damage:
The thermistor in the middle of the induction cooker coil is used to detect the temperature of the cookware, to prevent dry burning of the pan and to control the temperature of the food in the pan. When this thermistor is damaged, the induction cooker stops the power output (no heating) and displays the fault code.

The role of the thermistor in the power circuit
The role of NTC and PTC thermistors in the power supply circuit is described in the form of a question and answer.
Question 1: What is the main function of the NTC resistor in series in the AC circuit? How does it work?
Question 2: What is the main function of the varistor connected in parallel in the AC side circuit? How does it work! What would be the impact if there were no two components?

Induction cooker thermistor

The series connection of NTC resistors mainly plays the role of "current insurance" in the AC circuit.
The varistor is connected in parallel in the AC side circuit mainly to "limit the voltage super high". In order to avoid the inrush current generated in the electronic circuit at the moment of power-on, a power type NTC thermistor is connected in series in the power supply circuit, which can effectively suppress the inrush current at the time of starting. And after the completion of the suppression of the inrush current, the resistance value of the power type NTC thermistor will drop to a very small extent due to the continuous action of its current. It consumes negligible power and does not affect normal operating current. Therefore, the use of power-type NTC thermistors in the power supply circuit is the easiest and most effective measure to suppress the surge during startup to ensure that electronic equipment is protected from damage.
NTC thermistor suppresses inrush current during startup

Q: According to what you mean, it is better to put the varistor in the back of the fuse, so that the varistor will not cause any harm to the grid when it is turned on?
The fuses are generally slow! It is correct to use NTC. NTC has a high resistance when not energized. Once energized, the resistance is still high, limiting the inrush current. As the NTC has a current flowing through it, the temperature increases and the resistance drops to a very low level, which can be ignored.

However, in this case, the current is small and the resistance is small during normal operation. Then suddenly a surge current, or the circuit that makes the current increase, then it can not play a protective role, that is to say, the varistor can only be used to prevent surges when the power is on?

Basically there is no surge current after normal work, right?
Only surge voltage. If there is a surge current, such as a short circuit in the power supply, because the NTC has been turned on, it can't help it, only the fuse works. Remember that NTC is just boot protection. Imagine that if the circuit has been powered up normally, the NTC has low resistance, and when it encounters high voltage, the NTC is powerless to protect.

It is good to say that after a period of normal operation of the power supply, frequent switching on and off will cause damage to the power supply. Because at this time, due to the temperature rise of NTC, the resistance value decreases, and the ability to suppress surge is limited.
To be honest, NTC is used to suppress power surges that are booting up, and it is not possible to switch on and off frequently. Because it needs to wait for NTC cooling, return to its cold state resistance, it can be turned on again. Otherwise, the meaning of installing NTC is gone.
For small power supply current, small NTC does not heat up very much, so it has a certain effect.

I know that I use NTC resistors. If you use ordinary resistors + relays or thyristors, I wonder if it is OK?
Very good, much stronger than simply using NTC resistors, NTC will lose its inhibition when it is powered off and immediately powered up.
So frequent switching machines, NTC is invalid.
However, the thyristor's bias circuit does not work for a single resistor, and it is estimated that the high-power power supply will not work, so that the loss is a bit large. PTC is an insurance function and NTC is a limiting surge current.

NTC: Negative temperature resistance, the higher the temperature, the smaller the resistance, which is used to limit the startup surge current in the input loop. It generates heat during normal operation, and the resistance is reduced, which does not affect the work, but it consumes energy, and the power consumption cannot be ignored. NTC can also be used for temperature measurement.

PTC: Positive temperature resistor, string in the input loop. Also known as: resettable fuse. It generates heat when overcurrent, and the resistance increases, which is equivalent to the input disconnection. After cooling, the resistance is reduced and can continue to work without replacement. Often used with varistor, TVS.

Similar to the avalanche effect of the regulated DIODE, the current increases rapidly after the clamp voltage is exceeded, but does not short-circuit, which is different from the discharge tube.

PTC has many uses, such as the degaussing circuit of color TV, the starting circuit of refrigerator compressor and so on.
Over temperature protection sometimes uses PTC, which is in the loop PTC. NTC may be used, but PTC is equivalent to the role of the fuse, NTC is used to limit the starting current.

PTC is equivalent to a fuse

Keywords:Thermistor burnout causes

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