For an SCR , dv/dt protection is achieved through the use of

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RC across SCR

Explanation: SCR dv/dt protection is achieved by connecting a series RC circuit, known as a 'Snubber Circuit', in parallel (across) the SCR. This circuit limits the rate of rise of voltage across the device when it is in the OFF state, preventing accidental triggering due to junction capacitance.

Working Principle: When a fast-rising voltage is applied, the internal junction capacitance of the SCR ($C_j$) acts as a low-impedance path, causing a high charging current ($i = C \frac{dv}{dt}$) to flow. This current acts like a gate trigger, potentially turning the device ON prematurely. The external snubber capacitor $C_s$ provides an alternative path, while the series resistor $R_s$ limits the peak discharge current when the SCR turns ON.

Key Formulas: $i = C_j \frac{dv}{dt}$ — Charging current responsible for false triggering; $\frac{dv}{dt} \approx 0.632 \frac{V_s}{R_s C_s}$ — Approximation of voltage rise limit

Key Points: The snubber circuit prevents the voltage across the SCR from rising faster than its rated dv/dt capability.; The resistor $R_s$ is essential to limit the capacitor discharge current during the SCR turn-on process.; A snubber circuit is a standard passive protective component in power electronics converters.

Advantages: Prevents false triggering of the SCR.; Protects the SCR from high-voltage transients.

Disadvantages: Increases power loss in the circuit due to the resistor.; Adds extra volume and cost to the power circuit design.

Applications: AC-DC Converters (Rectifiers); AC Voltage Controllers; Inverters

Additional Info: The snubber capacitor also helps in suppressing high-frequency oscillations.. Option C (L in series) is used for di/dt protection, not dv/dt protection.

Answer: B is correct — An RC snubber circuit is connected in parallel with the SCR to limit the rate of rise of voltage (dv/dt) across it.

Exam Tip: Always remember: Series Inductor ($L$) provides di/dt protection, while a Shunt RC Snubber provides dv/dt protection.

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