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In a circuit what specifically are varistors used for ?

Varistors, also known as voltage-dependent resistors or VDRs, are electronic components used in circuits primarily for voltage regulation and protection against voltage spikes or surges. These components exhibit a nonlinear voltage-current characteristic, meaning their resistance decreases significantly with an increase in voltage. Varistors are employed in a variety of electronic and electrical systems for different purposes. Let’s delve into the specific applications and functions of varistors in a circuit:

1. Surge Protection:

  • Voltage Spikes and Surges:
    • Varistors are commonly used to protect electronic devices from voltage spikes and surges. These transient voltage events can occur due to lightning, switching operations, or other external factors.
  • Clamping Action:
    • Varistors act as voltage clamps. When the voltage across them exceeds a certain threshold, their resistance decreases, allowing them to conduct and divert excess current away from sensitive components, thus protecting the circuit.

2. Overvoltage Protection:

  • Sensitive Electronics:
    • Varistors are employed in circuits with sensitive electronic components, such as integrated circuits and semiconductor devices, to prevent damage caused by overvoltage conditions.
  • Quick Response:
    • Varistors respond rapidly to changes in voltage, offering a quick and effective means of protecting against overvoltage situations.

3. Voltage Regulation:

  • Stabilizing Voltage:
    • Varistors can be used in circuits to stabilize the voltage by providing a controlled resistance that varies with the applied voltage.
    • They are sometimes used in conjunction with other voltage regulation components to achieve a desired output voltage.

4. Suppressing Electromagnetic Interference (EMI):

  • Noise Filtering:
    • Varistors can help suppress electromagnetic interference by absorbing unwanted high-frequency noise generated by other components in the circuit.
    • They provide a shunting path for high-frequency signals, reducing interference in sensitive electronic systems.

5. Power Supply Protection:

  • Power Line Conditioning:
    • Varistors are used in power supply circuits to condition and protect against fluctuations and disturbances in the electrical supply.
    • They enhance the robustness of power supplies by mitigating the impact of voltage variations.

6. Lightning Arrestors:

  • Overhead Power Lines:
    • Varistors are employed in lightning arrestors for protecting overhead power lines and electrical distribution systems from lightning-induced voltage surges.
    • They help prevent damage to transformers, substations, and other critical components.

7. Automotive Applications:

  • Transient Protection:
    • Varistors are used in automotive circuits to protect electronic systems from voltage transients caused by events such as load dumps or sudden changes in battery voltage.
    • They contribute to the reliability of electronic control units (ECUs) in vehicles.

8. Telecommunications:

  • Equipment Protection:
    • Varistors play a crucial role in protecting telecommunications equipment, such as modems and routers, from voltage spikes induced by lightning or other disturbances on communication lines.

9. Inductive Load Protection:

  • Motor Control Circuits:
    • In circuits controlling inductive loads, such as electric motors, varistors are used to suppress voltage spikes generated during the switching of inductive loads.
    • This protects semiconductor devices like transistors and ensures the longevity of the motor control circuit.

10. Gas Discharge Tubes (GDT):

  • Combination with Varistors:
    • In some applications, varistors are used in combination with gas discharge tubes to provide additional protection against transient overvoltages.

Conclusion:

Varistors serve as versatile components in electronic circuits, offering valuable protection against voltage spikes, surges, and other transient events. Their nonlinear voltage-current characteristic and quick response make them essential for safeguarding sensitive electronic equipment and ensuring the reliable operation of various electrical systems. The specific application of varistors in a circuit depends on the requirements of the system and the nature of potential voltage-related disturbances.

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