Rectification is the process of converting alternating current (AC), which periodically reverses direction, into direct current (DC), which flows in only one direction. This is essential for powering electronic devices that require a steady DC supply from the AC mains.
A diode is the key component used in rectification because it allows current to flow in only one direction (forward-biased) and blocks it in the other (reverse-biased).
In half-wave rectification, a single diode is used to pass only one half-cycle of the AC input to the load.
| Half-Cycle | Diode State | Output |
|---|---|---|
| Positive | Forward-biased (low resistance) | Current flows through load |
| Negative | Reverse-biased (very high resistance) | No current flows |
Full-wave rectification converts both half-cycles of the AC input into a unidirectional output, making more efficient use of the input signal.
The most common full-wave rectifier uses four diodes (, , , ) arranged in a bridge configuration. No centre-tapped transformer is required.
Positive half-cycle (top terminal positive):
Negative half-cycle (bottom terminal positive):
In both cases, current through the load flows in the same direction, giving a full-wave rectified output.
| Property | Half-Wave | Full-Wave (Bridge) |
|---|---|---|
| Diodes required | 1 | 4 |
| Output frequency | ||
| Efficiency | ~40.6% | ~81.2% |
| Ripple | High | Lower |
The output of a rectifier is pulsating DC — it varies between zero and the peak voltage. A smoothing capacitor is connected in parallel with the load resistor to reduce this variation (called ripple).
The approximate peak-to-peak ripple voltage is:
where:
To reduce ripple:
Note: A full-wave rectifier with a smoothing capacitor produces much less ripple than a half-wave rectifier with the same capacitor, because the capacitor is recharged twice per cycle instead of once.