Introduction and application of varistor

The existence of resistance can ensure the safety of the circuit, so the resistance is an important component! SMD varistor is one of the common resistors, so do you know the working principle of SMD varistor? SMD varistors are generally used where, let me take you to find out.

The chip varistor is a chip packaged varistor, which is divided into two types of varistors from the package form. Plug-in varistors and chip varistors, varistors are generally used as gas discharge tube series and lightning surge protection, can also be used for electrostatic protection of various electronic/electric equipment, and chip varistors due to The package size is smaller, because it is suitable for electrostatic protection of highly integrated handheld electronic products nowadays.

From the above introduction, I believe it is not difficult for everyone to see that the chip varistor is actually an overvoltage/antistatic circuit protection device in a small package. Now that everyone knows the function of SMD varistor, let's understand the application of SMD varistor. The specifications and sizes of SMD varistors are diverse, from handheld electronic products to industrial equipment, I/O ports on the motherboard (RS232, USB, PS2, VGA, audio) and laptops, set-top boxes, and MP3 players , DVD players are inseparable from the protection of SMD varistors.

It is equivalent to a variable resistor, which is connected in parallel in the circuit. When the circuit is in normal use, the impedance of the varistor is very high, the leakage current is very small, it can be regarded as an open circuit, and it has almost no effect on the circuit. But when a very high surge voltage arrives, the resistance value of the varistor drops instantaneously (its resistance value can be changed from MΩ (megaohm) to mΩ (milliohm)), so that it can flow very large At the same time, the overvoltage is clamped to a certain value. Since the surge tolerance of the varistor depends on its physical size, it is possible to obtain different surge current values.

The salient feature of a varistor is that when the voltage applied to it is lower than its threshold "UN", the current flowing through it is extremely small, which is equivalent to a closed valve. When the voltage exceeds UN, its The resistance value becomes smaller, so that the current flowing through it increases sharply and the impact on other circuits does not change much, thereby reducing the impact of overvoltage on subsequent sensitive circuits. Using this function, the abnormal overvoltage that often occurs in the circuit can be suppressed, and the circuit can be protected from the damage of the overvoltage.