Page 326 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Single phase half wave controlled circuit

Single-phase controlled rectifiers, also known as phase-controlled rectifiers, play a crucial role in power electronics
applications. These devices are used to convert alternating current (AC) to direct current (DC) with the ability to
control the output voltage. This is achieved by adjusting the firing angle (or phase angle) of thyristors, which are
semiconductor devices capable of switching large currents.
A half-wave controlled rectifier utilizes a single thyristor that is connected in series with the load. Once triggered
at a specific firing angle during the positive half-cycle of the input AC supply, the thyristor begins to conduct, and
the output voltage waveform is determined by the firing angle and the input AC voltage amplitude. By adjusting
the firing angle, the average output voltage can be controlled, which affects the amount of power delivered to the
load. However, half-wave controlled rectifiers have the disadvantage of using only half of the input AC waveform,
resulting in high harmonic distortion and poor power circuit.

The output voltage can be changed by changing the firing angle α.

Single phase full wave half controlled bridge
The circuit diagram of single-phase full-wave half-controlled bridge is shown Fig. Two SCRs
and two diodes are used in this configuration. Single-phase a.c. supply is used as the input
to the bridge. It gives a full-wave rectified d.c. at its output. In the positive half of the input,
SCR and D are conducting while in the negative half, SCR and D are conducting and hence full wave
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rectification is obtained. The positive half of the input can be controlled by SCR when SCR remains idle. In the
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2
negative half cycle, SCR, is responsible for the control when SCR is idle. Hence, one half cycle of the input only
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CITS : E & H - Electronics Mechanic - Lesson 199 - 204