Rectifiers

Half Wave RectifiersHalf Wave Rectifier Tutorial

The voltage at point A does the opposite of that at point B.
When A is increasing in a positive direction, B is increasing in a negative direction.
It is rather like the two ends of a see-saw.

During the first half cycle of the waveform shown on the left, A is positive and B is negative.
The diode is forward biased and current flows around the circuit formed by the diode, the transformer winding and the load.

Since the current through the load, and the voltage across the load are in the same proportions, then the voltage across the load is as shown in the right hand diagram, during the first half cycle.
During the second half cycle, A and the anode are negative, B and the cathode are positive.
The diode is reverse biased and no current flows. This is indicated by the horizontal line in the right hand diagram.

The diode only conducts on every other half cycle.There is one pulse for every cycle in. i.e 50 pulses per second (in India)
The diode only conducts during half the cycle. Hence, HALF-WAVE RECTIFICATION.

The rectified voltage is DC (it is always positive in value). However, it is not a steady DC but PULSATING DC. It needs to be smoothed before it becomes useful.

If the diode is reversed then the output voltage is negative.

Full wave Rectifiers

The left hand waveform shows the input voltage (50 Hz AC in India).

The voltages at points A and B on the transformer are changing in opposite directions.
When A is increasing in a positive direction, B is increasing negatively.
It is like the opposite ends of a see-saw.
During the first half cycle, A is positive and B is negative.
D1 has positive on its anode, D2 has negative on its cathode.
Both are forward biased. Current flows around the circuit formed by these diodes, the load and the transformer winding, as shown in the second diagram. The current flowing up through the load produces a pulse of voltage across the load as shown in the right hand waveform.

During the next half cycle, A is negative and B is positive.
D4 has positive on its anode, D3 has negative on its cathode.
Both are forward biased.
Current flows around the circuit as shown in the bottom diagram, again flowing in the same direction through the load and producing another pulse of voltage.

Since the full cycle is used this circuit is called a FULL-WAVE rectifier.
Since there are two pulses for each cycle of input, there are 100 pulses per second out (in india).

The pulsating DC can be smoothed with a reservoir capacitor, as in the half-wave rectifier circuit.
Since the pulse frequency is higher than that of the half-wave rectifier, it is easier to smooth.