Rectifier

An electrical circuit which converts the AC current into DC current.Such process is known as rectification.There are two type of rectifier i.e

1)Half wave rectifier

2)Full wave rectifier

1)Half wave rectifier

Rectifier which rectified only half of its AC current to DC. Output is obtain only during alternating half cycle of input AC current.

Working process of half wave rectifier

Its working is based on the fact that the resistance of p-n junction become low when forward bias and become high when reverse bias.

The circuit diagram of half wave rectifier is shown in figure. Its consist of a Transformer a p-n junction diode 'D' and the load resistance 'RL'. The primary coil of the transformer is connected to the AC mains and the secondary coil is connected to the load resistance RL through the diode D. The DC output is drawn from the load resistance RL. During the positive half cycle of secondary voltage the diode D is forward bias therefore the current flow through the diode and the load resistance hence diode conduct easily.Similarly during half cycle of secondary voltage the diode act as reverse bias therefore there is no conduct of current through diode and load resistance. In this way half wave rectifier works.

2)Full wave rectifier

The rectifier which rectified full of its AC current to DC voltage.Output is obtained during both half cycle of its AC supply input. There is two type of full wave rectifier.

a)Center tapped full wave rectifier

Rectifier which rectified full of AC input to DC output by using two diode connected to the center tapped secondary coil of the transformer and load resistance 'RL'.

fig:a

fig:b

Working process of center tapped full wave rectifier

We have already discuss about full wave rectifier. It is based on the fact that the resistance of P-N junction becomes low when forward bias and become high resistance when reverse bias.

The circuit diagram of a full wave rectifier is shown in figure. The diode (D1 and D2) are connected to the center tapped secondary coil of the transformer and the load resistance (R) in such a way that the diode conduct during alternate cycle of the input AC supplied.

During positive half cycle of secondary voltage upper diode D1 is forward bias and lower diode D2 is reverse bias. Thus the current flows through diode D1 and load resistor R. During negative half cycle of secondary voltage upper diode D1 is reverse bias and lower diode D2 is forward bias. Thus the current flows through diode D2 and load resistor R.Here the half wave of input AC supplied Vin is rectified by one diode D1 and the next half wave is rectified by diode D2. Fig(b) show the rectified output voltage Vout obtain across the load resistor R for the supplied input AC voltage. The current flows through R are the same direction for both half cycle. Thus the output current through the load is said to be direct current.

b)Bridge rectifier

Rectifier which rectified full of AC input to DC output by using four diode connected to form a bridge.

Working process of bridge rectifier

Its working is based on the fact that the resistance of p-n junction become low when forward bias and become high when reverse bias.

The circuit  diagram of bridge rectifier  is shown in figure it consist of four diode D1,D2,D3 and D4 connected to form bridge. the input of acis applied across the primary coil  of the transformer the end of the secondary coil are connected to the two opposite end and the b and d are connected to the load resistance .The voltage drop across the load resistance give the output voltage.

When an AC input is applied to the primary coil of the transformer the voltage induced in the secondary coil .During positive half cycle of the secondary voltage suppose one end X of the secondary coil 'S', is positive and its other end Y is at negative. Then the diode D4 and D2 is forward bias and D1 and D3 are reverse bias. D2 and D4 conduct current through the load resistance and D1 and D doesn't conduct current.Again during the negative half cycle of secondary voltage suppose one end is Y at positive then the diode D2 and  D4 act as reverse bias so it doesn't conduct current but diode D1 and D3 act forward bias so they conduct current through the load resistance .In both cycle the current through cycle the AC input supplied is rectified full input dc. This way bridge rectifier work.