- Full Wave Rectifier Definition: A full wave rectifier is defined as a device that allows current to flow through the load during the entire cycle of the input voltage, using two or more diodes.
- Diode Configuration: In a full wave rectifier using diodes, each diode conducts during one half of the input voltage cycle.
- Center Tapped Transformer: A center tapped transformer is used with two diodes to achieve full wave rectification, where each diode conducts during alternate halves of the cycle.
- Bridge Rectifier: A bridge rectifier, made of four diodes, provides full wave rectification by ensuring the load current flows in the same direction during both halves of the input cycle.
- Waveform and Parameters: The input and output voltage waveforms are fully rectified, and important parameters include the average load current (Idc) and the ripple factor.
A rectifier diode conducts substantial forward current when forward voltage exceeds its operating threshold. A reverse-biased p-n junction diode ideally blocks, although real devices have leakage and voltage limits.
A centre-tapped two-diode circuit or four-diode bridge routes alternate halves of an AC voltage through the load in the same direction. The unfiltered output is pulsating DC and falls to zero at each ideal input zero crossing.
This process is called full wave rectification.
With a centre-tapped transformer, two p-n junction diodes D1 and D2 conduct on alternate half-cycles. Each half of the secondary supplies the same load polarity, so output voltage and current have twice the input frequency for a sinusoidal source.
Circuit Diagram of Full Wave Diode Rectifier
The following diagram shows the two-diode, centre-tapped full wave diode rectifier connection.
A bridge rectifier uses four diodes and does not require a centre-tapped source.
On the half-cycle shown, diagonal diodes D1 and D3 conduct while D2 and D4 block. The other diagonal pair conducts on the opposite half-cycle. Both paths send load current in the same direction, although each path includes two forward diode drops.
A bridge uses the full transformer secondary on both half-cycles and each reverse-biased diode generally needs a lower peak inverse-voltage rating than in the comparable centre-tapped circuit. The centre-tapped circuit has only one conducting diode drop per path, while the bridge has two. The better choice therefore depends on output voltage, current, transformer design, loss and cost.
Input Voltage and Output Voltage Waveform
The following ideal results for a resistive-load full wave rectifier assume a sinusoidal source and zero diode forward drop:
The average load current Idc is 2Im/π:
During either conducting interval, load-current magnitude is iL = Im|sin ωt|.
For an ideal unfiltered full-wave rectified sine, ripple factor is the RMS AC component divided by the DC component and equals approximately 0.482. A filter changes this value.
