This document discusses DC-DC converters known as choppers. It describes two types - step-down choppers and step-up choppers. A step-down chopper uses a thyristor switch to reduce input voltage to a lower output voltage for a load. Waveforms of the output voltage and current are shown. Different classes of choppers - Classes A through E - are defined based on the triggering schemes of the thyristors used. An example calculation is given to determine thyristor conduction period based on input voltage, output voltage, and operating frequency.
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Figure 2.1 shows a stepâdown chopper with resistive load.
The thyristor in the circuit acts as a switch. When thyristor is ON,
supply voltage appears across the load and when thyristor is OFF,
the voltage across the load will be zero. The output voltage and
current waveforms are as shown in figure 2.2.
Vdc
v0
V
V/R
i0
Id
t
tON tOFF
Idc
t
T
Fig. 2.2: Step-down choppers â output voltage and current waveforms
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Exercise
A Chopper circuit is operating on TRC at a
frequency of 2 kHz on a 460 V supply. If the load
voltage is 350 volts, calculate the conduction
period of the thyristor in each cycleperiod of the thyristor in each cycle.