It consists of a series combination of a resistor and a capacitor in parallel with the thyristors. It is mainly used for dv / dt protection.
The snubber circuit is used for the dv/dt protection of the SCR. It is a series combination of a resistor and a capacitor in parallel with the SCR.
- The snubber Circuit is a series combination of resistor ‘R’ and capacitor ‘C’.
- They are connected across the thyristor to be protected.
- The capacitor ‘C’ is used to limit the dv/dt across the SCR.
- The resistor ‘R’ is used to limit high discharging current through the SCR.
- When switch S is closed, the capacitor ‘C’ behaves as a short-circuit.
- Therefore voltage across SCR is zero.
- As time increases, voltage across ‘C’ increases at a slow rate.
- Therefore dv/dt across ‘C’ and SCR is less than maximum dv/dt rating of the device.
- The capacitor charges to full voltage Vs; after which the gate is triggered, and SCR is turned ON and high current flows through SCR.
- As di/dt is high, it may damage the SCR. To avoid this, the resistor R in series with ‘C’ will limit the magnitude of di/dt.
- The technique of ‘snubbing’ can apply to any switching circuit, not only to thyristor/triac circuits.
- The rate of rise of turn-off voltage is determined by the time constant
- RLC. Where RL is the circuit minimum load resistance, for instance the cold resistance of a heater or lamp, the winding resistance of a motor or the primary resistance of a transformer.