What is the role of varistor thermistor in power supply circuits?

Generally, it is necessary to avoid the harmful inrush current generated when switching on and off in the electronic circuit, so in the power supply circuit, we will generally connect a power thermistor in series, which can well suppress a surge current when switching on and off.

When the thermistor is connected in series in the AC circuit, it mainly plays the role of "current insurance", and the varistor block parallel connection plays the role of "limiting voltage ultra-high" in the AC circuit.

So how does a varistor work? Let's make an analogy here to explain that the "nominal 300 volts" varistor works at the voltage of 220 volts in our normal residential electricity, if it is said that once the accumulation rises to 310 volts, more than 300 volts, once such a situation occurs, our varistor electrical appliances will be broken down, after passing a large current, it will blow our fuse, once our fuse is blown it plays a role in protecting the circuit behind, in this case, The varistor will quickly return to its previous operating state.

However, whether it is a varistor or a thermistor after working for a period of time under the normal condition of the power supply, if we blindly switch on and off frequently, this will cause great damage to our power supply, which is mainly due to the temperature rise of the thermistor or varistor, and its relative resistance value will decrease, which will have a great impact on the surge suppression ability, indicating that its limiting ability is very limited.

As long as we understand the working principle of varistors and thermistors, they can be better used in power supply circuits.

Thermistors, which are generally strung in a circuit, do not heat up if they are below the rated current, and the resistance value remains the same. If the overcurrent is heated, the resistance value increases rapidly and plays a role in protecting the circuit.

The varistor is generally connected in parallel at the input end of the circuit, if the voltage exceeds the threshold of the varistor, the resistance of the varistor reduces the breakdown to protect the circuit behind, the resistance of the thermistor is affected by the temperature, and different temperatures have different resistance values, which are used as temperature sensors, such as monitoring the working temperature of the battery.

Varistor: It is a resistive device with nonlinear volt-ampere characteristics, which is mainly used for voltage clamping when the circuit is subjected to overvoltage, and absorbs excess current to protect sensitive devices. The resistive body material of varistors is semiconductors, so it is a variety of semiconductor resistors.

Now heavily used"Zinc oxide"Varistors, the main material of which is composed of bivalent zinc and hexavalent oxygen.

Thermistor: It is a type of sensitive element, which is divided into positive temperature coefficient thermistor and negative temperature coefficient thermistor according to different temperature coefficients. Thermistors are typically characterized by being temperature sensitive, exhibiting different resistance values at different temperatures.

Positive temperature coefficient thermistors have a higher resistance value when the temperature is higher, and negative temperature coefficient thermistors have a lower resistance value at higher temperatures, and they both belong to semiconductor devices.

Knowledge sharing: How to distinguish between varistors and thermistors.

A thermistor is a sensor that senses heat, and the higher the temperature, the smaller the resistance, and a varistor is a sensor that feels pressure, and the greater the pressure, the smaller the resistance.

One is heat control and the other is pressure control.