what is snubber and where it used?

A snubber is an electronic protection circuit, a snubber circuit is used for protection from malfunctioning of active components by high voltage “snubs” or surges in supply voltage. The snubber circuit is used in thyristor circuits for protecting the switching devices from false turn-on by surge voltage that is higher than its specified breakdown voltage. For example, an SCR is specified for up to 600V anode voltage. Then it may be turned on when a spike of near 600V occurs without a gate triggering. This voltage snub may not damage the SCR but malfunctions circuit operation. The snubber circuit for SCR suppresses surge voltage. And resist false switching of SCR.

Semiconductor switching devices are limited to a maximum breakdown voltage. At the above voltage level device conduct even in turned-off condition. An erroneous turning-on flows an undesired current from the load attached to the switching device. Although the applied voltage is predetermined in the circuit. But in practice semiconductor devices, wiring, and PCB tracks exhibit stray inductance and stray capacitance. This capacitance and inductance are also called parasitic capacitance and parasitic inductance. The parasitic inductance stores magnetic energy. And series and parallel practice capacitance and inductance generate ringing upon transient current and voltage. The ringing amplitude merges with the applied voltage in the graph, and the total voltage across the device is increased. An increment in voltage is a snub or surge.

Working principle of Snubber Circuit

A Snubber circuit may consist of a capacitor or a series RC circuit.  Sometimes it is employed with a diode. The Snubber circuit is connected parallel across the thyristor or the switching device. In the Capacitive snubber circuit, the capacitor stores transient voltage which is higher than biasing voltage. At the initial time of transient, the voltage drop across the thyristor slowly rises, even that transient voltage is passed. Thus, transient voltage is damped. In circuits, where the transient source has more surge energy then a small resistor in series of the capacitor is used. This resistor increases the charging time constant, dissipates transient energy and controls damping factor . This configuration is called the RC snubber circuit. RC circuit across a switching device disturbs switching parameters and performance. So, sometimes snubber circuit is designed as a diode in series with a parallel RC circuit. This configuration is called the RCD snubber circuit. In normal circuit operation, the Diode isolates the RC circuit from being an addition to the thyristor inductive load. Whenever switching occurs, the transient voltage which is more than the diode’s avalanche breakdown the diode conducts, and transient overvoltage is damped by the RC circuit. Thus, the RCD circuit keeps the thyristor or switching device safe and within the working limit. Even If the width of the transient pulse is wider.

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