Classification of Rectifier

Rectifier

A rectifier may be defined as an electronic device, such as a semiconductor diode, used for converting Alternate current voltage or current into unidirectional voltage or current.

Classifications of Rectifiers

Rectifier circuits are basically of two types depending on the alternating voltage they take as input. They are:

(a)     Single phase rectifiers

(b)     Polyphase rectifiers

Rectifiers may be classified in to two categories depending upon the period of conduction. They are

(a)     Half-wave rectifiers

(b)     Full–wave rectifiers

Full wave rectifiers may further be classified in to two categories depending upon nature of the circuit connection. They are

(a)     Centre tapped full-wave rectifier

(b)     Bridge full-wave rectifier

Half wave rectifier

A half wave rectifier circuit is one which conducts current only during the positive half cycles of input a.c. supply. The negative half cycles of a.c. supply are suppressed i.e. during negative half cycles, no current is conducted and hence no voltage appears across the load. Therefore current always flows in one direction through the load.

 The main disadvantages of half wave rectifier

1.       The pulsating current in the load contains alternating component whose basic frequency is equal to the supply frequency. Therefore, an elaborate filtering is required to produce steady current.

2.       The a.c. supply delivers power on half the time therefore, the output is low.

Full wave rectifier

In fill wave rectifier, current flows through the load in the same direction for both half cycles of input a.c. voltage. The commonly used full wave rectifier circuits are (1centretap full wave rectifier (2) full wave bridge rectifier.

Centre tapped full wave rectifier

The circuit employs two diodes and a Centre tapped secondary winding is used with two diodes connected so that each uses one half cycle of input a.c. voltage.in other words the first diodes utilizes the a.c voltage appearing across the upper half of secondary winding for rectification, while the second diode uses the lower half winding.

Disadvantages of Centre tapped full wave rectifier

1.       It is difficult to locate the Centre tap on the secondary winding.

2.       The d.c output is small as each diode utilizes only one half of the transformer secondary voltage.

3.       The diodes used must have high peak inverse voltage.

Full wave bridge rectifier

Full wave operation van be obtained even without the Centre tapped transformer in bridge rectifier. It contains fort diodes connected to form bridge. Alternating voltage is applied to the diagonally opposite ends of the bridge through the transformer. Between other ends of the bridge the load resistance is connected through the load. 

 Advantages and disadvantages of bridge rectifier

The following are advantages

1.       No centre tap is needed in the transformer secondary.

2.       The output is twice that of the centre tap circuit for the same secondary voltage.

3.       The peak inverse voltage is one half that of the centre tap circuit.

 The following are disadvantages

1.       It requires four diodes.

2.       As during each half cycle of a.c input two diodes that conduct are in series, therefore voltage drop in the internal resistance of the rectifying unit will be twice. This is objectionable when secondary voltage is small.