Working principle of step down chopper for R load

A step-down chopper with resistive load.

1) The thyristor in the circuit acts as a switch.

2) When thyristor is ON, supply voltage appears across the load

3) When thyristor is OFF, the voltage across the load will be zero.

Average\; output\; voltage\; V_O =\frac{1}{T}\int^{T_{ON}}_0 V_s dt = \frac{V_sT_{ON}}{T}=DV_s
Where, D is duty cycle = TON/T.

TON can be varied from 0 to T, so 0 ≤ D ≤ 1. Hence output voltage VO can be varied from0 to VS.
Therefore, Effective\; input\; resistance\;R_i=\frac{V_s}{T_{savg}}=\frac{V_s}{DV_s/R}=\frac{R}{D} so, we can conclude that output voltage is always less than the input voltage and hence the name step down chopper is justified. The output voltage and current waveform of step down chopper with resistive load is shown in above figure.