What is a varistor, and how does it protect electronic devices?
1 Answer
A varistor, also known as a voltage-dependent resistor (VDR), is an electronic component designed to protect electronic devices and circuits from voltage surges or transient overvoltages. It is commonly used in electronic devices, power supplies, and electrical systems to safeguard against potential damage caused by fluctuations in voltage.
Varistors are made of a semiconductor material with a nonlinear current-voltage characteristic. This means that the resistance of a varistor decreases as the voltage across it increases. In other words, varistors have a high resistance under normal operating conditions, but when the voltage exceeds a certain threshold (known as the "clamping voltage" or "breakdown voltage"), their resistance drops significantly, allowing a large amount of current to flow through the varistor.
The mechanism by which varistors protect electronic devices is as follows:
Normal Operation: Under normal voltage conditions, the varistor remains in a high-resistance state, acting like an open circuit. It does not interfere with the normal functioning of the circuit and does not conduct any significant current.
Voltage Surge or Transient: When a voltage surge or transient occurs in the circuit, such as a sudden increase in voltage due to lightning strikes, power line fluctuations, or switching events, the voltage across the varistor increases.
Conductive State: Once the voltage reaches the varistor's clamping voltage, it enters a low-resistance state. At this point, the varistor begins to conduct a large amount of current, effectively shunting the excess voltage away from the sensitive components in the circuit.
Protection: By diverting the excess current away from the sensitive components, the varistor protects them from being damaged by the high voltage. The varistor dissipates the excess energy as heat, which is usually well within its capacity to handle.
It's important to note that while varistors are effective at protecting against voltage surges and transients, they have a limitation to the amount of energy they can handle. In cases of severe or prolonged overvoltages, the varistor might not be able to dissipate all the energy, and it could fail. To enhance protection, varistors are often used in conjunction with other protective devices like fuses, circuit breakers, or gas discharge tubes (GDTs).
In summary, varistors are essential components in modern electronics to safeguard against voltage fluctuations and protect sensitive devices from damage caused by transient overvoltages. They offer a cost-effective and efficient means of surge protection for a wide range of electronic applications.
Varistors are made of a semiconductor material with a nonlinear current-voltage characteristic. This means that the resistance of a varistor decreases as the voltage across it increases. In other words, varistors have a high resistance under normal operating conditions, but when the voltage exceeds a certain threshold (known as the "clamping voltage" or "breakdown voltage"), their resistance drops significantly, allowing a large amount of current to flow through the varistor.
The mechanism by which varistors protect electronic devices is as follows:
Normal Operation: Under normal voltage conditions, the varistor remains in a high-resistance state, acting like an open circuit. It does not interfere with the normal functioning of the circuit and does not conduct any significant current.
Voltage Surge or Transient: When a voltage surge or transient occurs in the circuit, such as a sudden increase in voltage due to lightning strikes, power line fluctuations, or switching events, the voltage across the varistor increases.
Conductive State: Once the voltage reaches the varistor's clamping voltage, it enters a low-resistance state. At this point, the varistor begins to conduct a large amount of current, effectively shunting the excess voltage away from the sensitive components in the circuit.
Protection: By diverting the excess current away from the sensitive components, the varistor protects them from being damaged by the high voltage. The varistor dissipates the excess energy as heat, which is usually well within its capacity to handle.
It's important to note that while varistors are effective at protecting against voltage surges and transients, they have a limitation to the amount of energy they can handle. In cases of severe or prolonged overvoltages, the varistor might not be able to dissipate all the energy, and it could fail. To enhance protection, varistors are often used in conjunction with other protective devices like fuses, circuit breakers, or gas discharge tubes (GDTs).
In summary, varistors are essential components in modern electronics to safeguard against voltage fluctuations and protect sensitive devices from damage caused by transient overvoltages. They offer a cost-effective and efficient means of surge protection for a wide range of electronic applications.