This section provides overview, applications, and principles of varistors. Also, please take a look at the list of 26 varistor manufacturers and their company rankings.
A varistor is a semiconductor device with two electrodes whose resistance changes depending on the applied voltage.
The word "varistor" means "variable" and "resistor," i.e., "resistance that changes.
For this reason, it is sometimes called a non-direct resistance or a voltage-dependent resistance.
Voltage and current are not proportional to each other. When the voltage applied to the varistor is low, the resistance is high, and when the voltage is high, the resistance is low.
Another characteristic of varistors is that they have symmetrical current-voltage characteristics and therefore have no polarity.
Varistors vary in resistance according to voltage.
This characteristic can be used to protect IC elements from static electricity or to protect electronic equipment from lightning surges.
If an abnormal voltage is applied to an element, such as an IC or an electronic device, it may cause malfunction or destruction.
In addition, when a high voltage is applied to varistors, the resistance of the varistors becomes low.
This allows current to flow through the circuit more easily, and the voltage drop in the line impedance reduces the load on the electronic equipment.
Varistors characteristics can be expressed as I=KV^α, where I is the current and V is the voltage.
Where K is a constant specific to the device and α is the voltage non-linearity coefficient (α coefficient).
The voltage non-linearity coefficient is a coefficient that expresses the curvature after the refraction point, the point where the resistance transitions from low to high.
The equivalent circuit of varistors consists of two upside-down Zener diodes connected in parallel with a capacitor.
From this we can see that the varistors have a capacitor component, which means that the voltage applied to the varistors is low, and that the varistors have a small amount of capacitance when it has a high resistance.
In other words, although the varistors show high resistance up to a certain voltage, when a load exceeding a certain voltage is applied, the resistance suddenly drops and a large current flows due to the quantum mechanical tunneling effect.
Therefore, when a high-voltage load is applied to an element or electronic device, the varistors play the role of releasing static electricity to ground and so on.
*Including some distributors, etc.
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