What is the underlying working principle of a varistor? Why is its resistance large when the voltage is small, and suddenly becomes smaller when the voltage is large?

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What is the underlying working principle of a varistor? Why is its resistance large when the voltage is small, and suddenly becomes smaller when the voltage is large? [Copy link]

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What is the underlying working principle of a varistor? Why is its resistance large when the voltage is small, and suddenly becomes smaller when the voltage is large? What are the specific requirements for its response time? For example, if it is required to respond within 1 microsecond, but it can only respond in 1 millisecond, then its performance is definitely not up to standard.

maychang

The working principle of the varistor is similar to that of the Zener diode in the electronic circuit, both of which involve the breakdown of the PN junction.

The varistor is made of sintered zinc oxide powder, and the manufacturing process is similar to that of firing ceramics. After the ceramic sheet is made, silver is coated on the two end faces of the ceramic sheet, and then the leads are welded. From the circuit point of view, it is similar to many PN junctions mixed together, some in series and some in parallel. When the voltage across the varistor is relatively low, none of the PN junctions is broken down, and the resistance between the two electrodes is high. When the voltage between the two electrodes reaches a certain value, some PN junctions are broken down, causing more PN junctions to be broken down, and the resistance between the two electrodes becomes quite low.

maychang

The nonlinearity of the varistor is obviously not as good as that of a single Zener diode or TVS. However, its response time is fast enough, generally within 1us.

Obviously, the transition voltage of the varistor is related to the thickness of the ceramic sheet. The thicker the ceramic sheet, the higher the transition voltage. The energy it can withstand in a single discharge is related to the volume of the ceramic sheet. The larger the volume, the greater the energy it can withstand in a single discharge.

maychang

From the structure of the varistor, we know that the varistor can be regarded as a number of PN junctions connected in parallel and series. Therefore, the capacitance of the varistor is quite large, much larger than the capacitance between the two electrodes of the varistor, because it is equivalent to many diodes connected in parallel and series.

chunyang

The underlying working principle of the varistor is Zener breakdown. Its basic structural unit is a reverse series Zener diode composed of a metal oxide, and such Zener diodes are then connected in parallel and series to form the whole varistor.

For the response time, check the device manual. If the varistor you buy complies with the device manual, it is qualified.

se7ens

After reading the answers from the two great masters, I learned new knowledge. This is a very good question.

吾妻思萌

The characteristics of piezoelectric ceramics, why is a semiconductor a semiconductor? Because of its characteristics

langtuodianzi

Learned

zxw517

Been taught a lesson