Step Down Chopper with Resistive Load


Step down chopper is used to step down the dc voltage. The circuit diagram of step down chopper with resistive load is given in Fig. 1. The step-down chopper has input voltage of 220 V and resistance of 10 Ω. The switch (S1) is operated with signal of 1 kHz switching frequency and 50 % duty cycle.

Fig. 1 Circuit diagram of step-down chopper with resistive load.
Step-down chopper operates in two mode. 

Mode-1: When the switch is ON, the switch voltage, VSW is 2 V, output voltage, vo is (VS - VSW), and output current, io is (vo /R).

Fig. 2 Equivalent circuit of step-down chopper with resistive load during mode-1.

Mode-2: When the switch is OFF, the output voltage and current are zero.

Fig. 3 Equivalent circuit of step-down chopper with resistive load during mode-2.
Waveform showing switching signal (S1), input voltage (VS), output voltage (vo), and output current (io) for step down chopper with resistive load is given in Fig. 4.

Fig. 4 Waveforms for step-down chopper with resistive load.
The average and RMS value of output voltage for step-down chopper can be obtained with following formulas.

Average Output Voltage, Va = (V- VSW) ✕ ( TON / (TON+TOFF) )
Va = (220 - 2) ✕ ( 0.0005 / (0.0005+0.0005) )
Va = (220 - 2) ✕ ( 0.5 ) = 109 V

RMS Output Voltage, VO(V- VSW) √ (TON/(TON+TOFF))
VO = (220 - 2) √ (0.5) = 154.15 V

Reference

M. H. Rashid, “Power Electronics: Circuits, Devices and Applications,” Prentice Hall India, Second Edition, 2006.

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