Full Wave Rectifier
A full wave rectifier is a circuit that allows the flow of current in only one direction, ensuring that the output voltage remains positive throughout. The primary purpose of a full wave rectifier is to convert AC power into DC power, which is essential for many electronic devices and systems. The negative half-cycles of the sinusoidal input waveform are eliminated, thereby ensuring a steady and continuous current flow in a single direction. Full wave rectifier finds applications in various domains, including power supplies, battery charging systems, audio amplifiers, and radio receivers.
Circuit Types of Full Wave Rectifiers
There are two main circuit types of full wave rectifiers: center-tapped and full wave bridge rectifiers.
Center-Tapped Full Wave Rectifier
A center-tapped full wave rectifier consists of a transformer with a center-tapped secondary winding and two diodes. The center-tapped transformer divides the secondary winding into two halves, allowing for a more efficient conversion of AC to DC. During the positive half-cycle of the input AC voltage, one of the diodes becomes forward-biased and conducts, allowing current to flow through the load connected to the output terminals. Simultaneously, the other half of the secondary winding remains in the reverse bias state. During the negative half-cycle, the polarity reverses, causing the other diode to conduct, thus ensuring a continuous flow of current through the load resistance in the same direction. This configuration allows both halves of the input AC cycle to be utilized, resulting in a higher efficiency than half-wave rectifiers.
Full Wave Bridge Rectifier
The full wave bridge rectifier uses four diodes arranged in a bridge configuration. The input AC voltage is applied across two opposite corners of the bridge, while the output DC voltage is obtained across the load resistance. During each half-cycle of the AC input voltage, two diodes become forward-biased, and the other two diodes become reverse-biased. This configuration allows current to flow through the forward-biased diodes and toward the output terminal, resulting in a unidirectional current flow and a higher average output voltage than a half-wave rectifier. However, it is essential to note that the output of a bridge rectifier is still a pulsating DC, containing ripples that can be reduced using a capacitor filter.
The performance of a full wave rectifier can be evaluated based on several key metrics, including:
1. Ripple Factor (γ)
This metric quantifies the amount of AC component or ripple in the rectified output. It is calculated using the formula:
- Vrms is the RMS (root mean square) value of the AC component of the output voltage.
- VDC is the DC component of the output voltage.
The ripple factor for a full wave rectifier is approximately 0.48, assuming an ideal condition (no load resistance or filtering).
2. Rectification Efficiency (η)
It measures the efficiency of the rectifier in converting AC input power into DC output power. The rectification efficiency (η) can be calculated as:
- PDC is the DC output power.
- PAC is the AC input power.
A full-wave rectifier’s rectification efficiency is higher than a half-wave rectifier. It is around 81.2% under ideal conditions.
3. Peak Inverse Voltage (PIV)
It refers to the maximum voltage across the diodes in the reverse-biased direction during the negative half-cycle of the input AC. For a full wave bridge rectifier, the PIV across each diode is equal to the peak value of the input AC voltage.
- Vpeak is the peak value of the input AC voltage.
4. Form Factor (FF)
Form factor is a measure that indicates the shape or form of the output waveform concerning its average or RMS (root mean square) value. For a full wave rectifier, the form factor is given by the ratio of the RMS value to the average value of the output voltage. It is expressed as:
- Vrms is the RMS value of the output voltage.
- Vavg is the average value of the output voltage.
For a full wave rectifier, the output voltage is a pulsating DC with ripple, and the form factor is approximately 1.11, assuming ideal conditions and no load resistance or filtering.
5. Peak Factor (PF)
Peak factor is a measure that indicates the ratio of the peak value of the output voltage to its RMS value. It quantifies the extent of variation or peaks in the waveform compared to its average value. The peak factor for a full wave rectifier is calculated as:
- Vpeak is the peak value of the output voltage.
- Vrms is the RMS value of the output voltage.
The peak factor for a full wave rectifier is approximately 1.414, considering ideal conditions.
Article was last reviewed on Saturday, December 30, 2023