Rectifier

RECTIFIER

Rectifier is a circuit which changes the direction of current i.e. it converts alternating current (AC) into direct current (DC). The rectifier consists of several diodes based on the circuit used; the rectifiers are classified into three types:

1. Half wave rectifier

2. Full wave rectifier

3. Bridge rectifier

Half wave rectifier:

The half wave rectifier is circuit consists of a single diode which converts alternating current into pulsated direct current.

The below circuit diagram show half wave rectifier

The half wave rectifier converts only positive half cycle of the alternating current. The above circuit consists of step down transformer is connected to diode and the load resistance. When alternating signal allow in the circuit the diode allows only positive half cycle, hence negative half cycle is eliminated.

*The wave forms obtained for half wave rectifier is given below:

Observe the wave form you would notice that a gap is left between two positive half cycles. The gap is due to absence of negative half cycle.

*The efficiency of half wave rectifier is 25%

Full wave rectifier:

The full wave rectifier is a circuit consists of two diodes which convert alternating current into complete direct current. The circuit diagram is shown below:

The full wave rectifier converts both positive and negative cycles into unidirectional form. The above circuit consists of step down center tapped transformer; the secondary side of a transformer is connected to diodes.

*The wave forms obtained by full wave rectifier are given below:

Operation:

1. When AC supply is given to the full wave rectifier, the

transformer steps down the voltage to 9V.

2. In full wave rectifier both the diodes are operated simultaneously

3. When diode D1 conducts the D2 is in OFF mode, then D1 conducts positive half cycle

4. When diode D2 conducts the D1 is in OFF mode, then D2 conducts negative half cycle

*Form the view of wave forms compare with half wave rectifier the gap between two positive cycles is filled with negative cycle which is converted by diode D2. Hence continuous current mode operation takes place.

*The efficiency of full wave rectifier is 50%.

Bridge rectifier:

The function of Bridge rectifier is similar to the Full wave rectifier; the only difference is high output efficiency and strandization. The below circuit belongs to Bridge rectifier.

The bridge rectifier consists of four diodes named D1, D2, D3, D4 and a load resistance.

Operation:

1. when AC supply is given to the transformer reduces the voltage upto 9V. This 9V secondary voltage of transformer is fed to the bridge of diodes.

2. At first for producing positive half cycle the diodes D1 and D3 are in forward bias and the diodes D2 and D4 are in reverse bias, hence no conduction takes place in reverse bias.

3. When D2 and D4 are in forward bias the negative half cycle is rectified, at this time D1 and D3 are in non-conducting mode.

4. By the action of four diodes the alternating current is converted into direct current as shown in below wave forms:

*The output is measured at load resistance.

*The efficiency of Bridge rectifier is 75%.