Rectifiers and Types of rectifiers

RECTIFIERS

The “rectifier” is a circuit that converts AC voltages and currents into pulsating DC voltages and currents. It consists of DC components and the unwanted ac ripple or harmonic components which can be removed by using filter circuit. Thus the output obtained will be steady DC voltage and magnitude of DC voltage can be varied by varying the magnitude of AC voltage.

Filters: A circuit that removes ripples (unwanted ac components) present in the pulsating dc voltage.

Regulator: A circuit that maintains the terminal voltage as constant even if the input voltage or load current varying.

Types of rectifiers:

Rectifiers are grouped into two categories depending on the period of conduction.

(a)Half wave rectifier               (b) Full wave rectifier

Half wave Rectifier:

Principle

It is a circuit that converts alternating voltage or current into pulsating voltage or current for half the period of input cycle hence it is named as “half wave rectifier”.

Construction

^Ø   It consists of step-down transformer, semiconductor diode and the load resistance.

^Ø   The step-down transformer – reduce the available ac voltage into required level of smaller ac voltage.

^Ø   The diode can be used to convert the ac into pulsating dc.

Operation

^Ø   During the positive half cycle of input, the diode D is forward biased, it offers very small resistance and it acts as closed switch and hence conducts the current through the load resistor.

^Ø   During the negative half cycle of the input diode D is heavily reverse biased, it offers very high resistance and it acts as open switch hence it does not conduct any current. The rectified output voltage will be in phase with AC input voltage for completely resistive load.

Full wave Rectifier:

Principle

A circuit that converts the ac voltage or current into pulsating voltage or current during both half cycle of input is known as “full wave rectifier”.

Operation

^Ø   During positive half cycle of ac input, diode D₁ becomes forward biased, provides very small resistance and acts as closed switch, resulting in the flow of current.

^Ø   During negative half cycle, diode D₁ reverse biased, offers high resistance and it acts as open circuit.

Voltage Regulation:

Ratio of Difference of secondary voltage to Primary voltage to secondary voltage.