## Full wave bridge rectifier:

This post provides an information about full wave bridge rectifier. We will also see its working principle and advantages and disadvantages.

Full wave bridge rectifier circuit diagram

In full wave Bridge rectifier a transformer and four diodes are used. During the positive half cycle of secondary voltage, the diodes D2 and D4 are forward-biased, but diodes D1 and D3 do no conduct. The current is through D2, R, D4 and secondary winding.

During the negative half cycle, the diodes D1 and D3 are forward-biased, but diodes D2 and D4 do not conduct. The current is through D1, secondary winding, D3 and R.

The load current is in the same direction in both half-cycles. Therefore a unidirectional (d.c.) voltage is obtained across load resistor.

Average voltage = Vdc = 0.636 Vp = 2Vp/p

Where Vp = peak value of secondary voltage.

Since each diode conducts for only half cycle, the current rating (Io) of the diodes must be at least – half of the dc load current. i.e. 0.5 Idc.

Each diode must withstand a peak inverse voltage equal to the peak secondary voltage. PIV = Vp.

Therefore the PIV rating of the diodes must be greater than Vp. As the output is a full-wave signal, the output frequency is double the input frequency.

The maximum efficiency of bridge rectifier is 81.2%

Advantages of full wave bridge rectifier:

• Centre tap on the secondary of the transformer is not necessary.
• Small transformer can be used.
• For a bridge rectifier circuit PIV per diode is one-half of the value for each diode in a full-wave rectifier.

• In this type two extra diodes are used.
• The voltage regulation is poor.

## Half Wave Rectifier:

This post provides an information about half wave recifier and its working principle.

half wave rectifier

In this type only one diode is used. Generally a step-down transformer is used to provide the required secondary voltage. The transformer isolates the load from the line. This reduces the possibility of electric shock.

In the positive half cycle of secondary voltage, the diode is forward biased for voltages greater than the offset voltage. The offset voltage is 0.7 V for silicon diodes and 0.3 V for germanium diodes. This produces a half sine wave of voltage across the load resistor.

In the negative half cycle, the diode is reverse biased. The load current drops to zero.

The load current is always in the same direction. This provides rectification.

Average Voltage = Vdc = Vp/p = 0.318 Vp

Where, Vp = peak value of voltage across secondary. The value of direct current, the diode can handle is called as ‘Current rating of diode’ (Io).

Peak Inverse Voltage ā In the negative half – cycle, the diode is reverse-biased. All secondary voltage appears across the diode. The maximum negative (reverse) voltage appearing across the diode is called the ‘Peak Inverse Voltage’ (PIV). To avoid break down, the PIV must be less than PIV rating of the diode. For half wave rectifier PIV = Vp.

Maximum efficiency of half wave rectifier is 40.6 %.