A rectifier circuit that only rectifies the positive half cycle or negative half cycle of the input sinusoidal signal is known as a half-wave rectifier.

An electronic device that converts a sinusoidal AC signal to a pulsating DC signal is known as a rectifier. This process of conversion of AC signal to DC signal is known as rectification.

Illustration

Half-Wave Rectifier

Here a step-down transformer is used whose primary side is connected to the AC signal and the secondary side is connected to a diode in series with a load resistance RL.

Half-Wave Rectifier

During the positive half cycle of the AC signal, the P site of the diode is in higher potential compared to the N side. So, the diode is forward biased i.e. the diode gets ON and conducts current for the positive cycle of the input signal. Hence current flows in the circuit and there will be a voltage drop across the resistor.

During the negative half cycle of the input AC signal, the N side of the diode is in higher potential compared to the P side. So, the diode is reverse biased i.e. the diode gets OFF and does not conduct current for the negative half cycle of the input AC signal. Therefore, the voltage and current remain zero for the load.

Here, the output of the rectifier consists of a ripple. It means that the output is not a constant DC. To make this signal ripple-free, a shunt capacitor is connected across the load.

Half-Wave Rectifier with Shunt Capacitor Filter

Half-Wave Rectifier

Half-Wave Rectifier

The shunt capacitor used above will help to filter the output rectified signal. When the diode is forward biased during the positive half cycle, the diode conducts current. During this period capacitor charges quickly to the peak value of the supplied voltage C capacitor charges up to point b. The capacitor will hold the charge or energy until the input supply to the rectifier goes negative.

When the diode is reverse biased during the negative half cycle there is no conduction of current. During this period capacitor, discharges through RL. The voltage across the capacitor VC decreases exponentially with time constant RLC. The time constant must be large enough so that the capacitor maintains the sufficiently high voltage across the load during the negative half cycle.

When the rectified voltage exceeds the capacitor voltage VC during the next positive half-cycle (given by point ‘c’ in the waveform) the capacitor again gets charged up to Vsmax or VLmax( point ‘d’ on the waveform).

The process of charging and discharging the capacitor is repeated until the input supply is present and output is fairly maintained to a constant voltage.


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