A rectifier uses diodes to make alternating current flow one way only. Half-wave and full-wave rectifiers differ in how much of the input they use.
This lesson is part of SPM Physics electronics. It relies on the one-way action in interpreting diode behaviour.
How do the outputs compare?
| Half-wave | Full-wave (bridge) | |
|---|---|---|
| Diodes | 1 | 4 |
| Uses | one half of each cycle | both halves of each cycle |
| Output shape | humps with gaps | humps with no gaps |
| Pulses each second from 50 Hz | 50 | 100 |
All the humps point the same way, so the load gets current in one direction.
Worked example: describing the half-wave output
The input is an a.c. sine wave. During the half cycle that makes the diode forward biased, the current flows and the output follows the input.
During the other half cycle, the diode is reverse biased and blocks. The output is zero. The graph is a row of humps with a flat gap after each one.
Worked example: adding a smoothing capacitor
Connect a capacitor across the load. While the voltage rises, the capacitor charges to the peak. When the input falls, the capacitor discharges through the load and keeps the voltage up.
The next hump recharges it before it drops far. The output is now a slightly wavy line near the peak value, called ripple, instead of separate humps.
The mistake that loses marks
A student writes “the rectifier makes a steady direct current”. A rectifier alone gives a direct but varying current, because the humps still rise and fall.
The accurate statement is “current flows in one direction only”. To call the output smoothed, you need the capacitor, and even then a small ripple remains.
Check yourself
The mains frequency is 50 Hz. How many output pulses each second does a full-wave rectifier give, and what does adding a capacitor do?
Answer
Each of the two half cycles in a cycle gives a pulse, so 2 × 50 = 100 pulses each second.
The capacitor charges at each peak and discharges between peaks, so the output is smoother, with a small ripple.
What to study next
Go on to reading transistor circuit functions. See the waveforms on a screen in explaining electron-beam and electronic-device principles.
Test yourself with the practice set. If you want a teacher to go through your output graphs with you, see online one-to-one Physics tuition.