LM2904N Varistor is a special resistance device, whose resistance value will change when affected by external voltage. When the external voltage is lower than its working voltage, the resistance value of the varistor is very high, and it almost cannot pass the current; When the external voltage exceeds its working voltage, the resistance value of the varistor will rapidly decrease, thus forming a low resistance path that absorbs excess current for protection.
The protection function of varistor is mainly based on its special material and structure design. The following details how the varistor absorbs excess current for protection.
1. Varistor material
The main material of varistor is zinc oxide (ZnO), which has nonlinear resistance characteristics. When the external voltage is lower than the working voltage, the zinc oxide is in the insulation state, and the ability of current passing through the material is very low; When the external voltage exceeds the working voltage, the conductivity of zinc oxide will greatly increase, forming a low resistance path.
2. Varistor structure
A varistor is usually composed of two electrodes and a dielectric layer. The electrode is usually made of metal materials (such as silver, copper, etc.) by printing, spraying, etc. The medium layer is the accumulation of zinc oxide particles, also known as the pressure sensitive layer. When the external voltage is lower than the working voltage, the dielectric layer of the varistor is isolated and the current cannot pass through; When the external voltage exceeds the working voltage, the dielectric layer of the varistor becomes conductive and the current can pass through.
3. Operating principle
When the external voltage is lower than the working voltage, there are a lot of insulating oxides between the zinc oxide particles of the varistor, and the current cannot pass through. However, when the external voltage exceeds the working voltage, the external electric field will destroy the insulating oxide, so that a conductive channel will be formed between zinc oxide particles, thus forming a low resistance path and absorbing excess current.
4. Protection function
The main protection function of the varistor is to prevent other components in the circuit from being damaged by overcurrent by absorbing excess current. When the external voltage exceeds the working voltage, the resistance value of the varistor rapidly decreases, forming a low resistance path that absorbs and distributes the excess current to the ground or other safe places. By absorbing excess current, the varistor can protect other components in the circuit from being damaged by overcurrent.
Summary:
Through its special material and structure design, varistor can absorb and protect excess current. When the external voltage exceeds the working voltage, the varistor will form a low resistance path, absorb the excess current and disperse it to the ground or other safe places. The varistor plays an important role in protecting the circuit, which can prevent other components from being damaged by overcurrent.
