Latching current for an SCR is 100 mA, a dc source of 200 V is also connected to the SCR which is supplying an R-L load. Compute the minimum width of the gate pulse required to turn on the device. Take L = 0.2 H & R = 20 ohm both in series

To compute the minimum width of the gate pulse required to turn on an SCR given the parameters:

– Latching current (I_L) = 100 mA = 0.1 A

– DC Source Voltage (V) = 200 V

– Inductance (L) = 0.2 H

– Resistance (R) = 20 Ω

1. Determine the time constant (τ):

The time constant (τ) for an RL circuit is given by:

[

τ = frac{L}{R}

]

Substituting the given values:

[

τ = frac{0.2 , text{H}}{20 , Omega} = 0.01 , text{s} = 10 , text{ms}

]

2. Determine the voltage across the load:

The voltage across the load can be calculated using Ohm’s law:

[

V_R = I cdot R

]

In steady state, the maximum current (I) can be found from:

[

I = frac{V}{R} = frac{200 , V}{20 , Omega} = 10 , A

]

3. Get the required rise time to reach the latching current:

The current through the inductor can be expressed as: