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 determine the minimum width of the gate pulse required to turn on the SCR, we need to consider the behavior of the R-L load circuit.

1. Calculate the time constant (τ) of the RL circuit:

The time constant ( τ ) is given by:

[

τ = frac{L}{R}

]

where:

– ( L = 0.2 , text{H} )

– ( R = 20 , Omega )

Substituting the values:

[

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

]

2. Calculate the current through the load when the SCR is turned on:

The current through the R-L circuit reaches its steady-state value given by:

[

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

]

This is the maximum current after a sufficient time has passed after the SCR turns on.

3. Determine the minimum pulse width needed:

To turn on the SCR, the gate pulse must provide enough time for the current through the SCR to reach the latching current (100 mA). We’ll calculate this based on the exponential growth of current in an