What it does
Mains electricity is AC: it pushes one way, then the other, 50 times a second. Phones, radios and LEDs need DC, which always pushes the same way. A diode only lets current through one way, so a few diodes can turn AC into DC. That is a rectifier.
- Half-wave. One diode. It passes the positive half of each cycle and blocks the negative half, so the load gets one pulse per cycle and nothing in between.
- Full-wave (centre-tap). A transformer with a tap in the middle of its secondary coil and two diodes. In each half cycle one diode conducts, so both halves reach the load the same way round: two pulses per cycle.
- Bridge. Four diodes in a diamond, no centre tap needed. Two diodes conduct in the positive half and the other two in the negative half; the current always goes through two of them, so 1.4 V is lost instead of 0.7 V.
- Smoothing capacitor. A capacitor across the load charges up at each peak and feeds the load while the input falls. The output becomes nearly steady DC with a small saw-tooth ripple. A bigger capacitor or a lighter load (bigger RL) gives less ripple.
Tap Positive half and Negative half to see which diodes conduct (they turn coloured). The wave plot shows the input (dashed) and the output across the load (solid) over three cycles.
This fits Class 12 Physics: semiconductor electronics (the diode as a rectifier, half-wave and full-wave rectifiers, filtering with a capacitor). Start with how one diode behaves in the PN junction tool; see how a capacitor stores charge in the parallel-plate capacitor lab, and build any circuit of your own in the circuit simulator.
How to use it
- Choose Half-wave, Full-wave or Bridge.
- Switch between the two half cycles to see the current path.
- Set the peak input voltage Vp and the load RL.
- Pick a smoothing capacitor and read the DC output, the lowest output, the ripple and the ripple factor.
- Compare the simulated numbers with the textbook estimates under the plot.
Worked example
Bridge, Vp = 12 V, RL = 1 kΩ, no capacitor: the peak output is 12 − 2 × 0.7 = 10.60 V. The textbook average 2Vm/π gives 6.75 V; the simulation gives 6.29 V, a little less because each pulse starts only once the input passes 1.4 V. The output drops to 0 V between pulses (ripple 10.60 V) and the ripple factor is 0.572.
Add 1000 µF. The output now stays between 10.50 V and 10.60 V: ripple 0.10 V at 100 Hz, DC output 10.55 V. The estimate Vr ≈ 10.60 / (100 × 1000 × 0.001) = 0.11 V agrees. Now lower RL to 200 Ω: the capacitor drains faster and the ripple grows to 0.47 V.
Half-wave with 1000 µF and 1 kΩ: the ripple is 0.22 V, about twice the bridge’s, because the capacitor has to last a whole 20 ms cycle instead of 10 ms.
Tips
- The ripple frequency tells you the type: 50 Hz for half-wave, 100 Hz for full-wave and bridge on 50 Hz mains.
- The estimate Vm/(f R C) only works when the ripple is small; with 100 µF and a heavy load it overestimates.
- Real supplies add a voltage regulator after the capacitor (a Zener diode is the simplest; see the p-n junction tool).
FAQ
Why does a bridge need four diodes when full-wave needs two? The centre-tap circuit uses half of the transformer coil in each half cycle; the bridge uses the whole coil both times, so it needs two more diodes to steer the current.
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Is this an official textbook tool? No. It is an independent practice page that follows the same school topics.
Where the numbers come from
- Half-wave, full-wave and bridge rectification, the averages Vm/π and 2Vm/π, the ripple estimate Vr ≈ Vm/(f_r R C) and the 0.7 V silicon diode drop are standard school physics and electronics.
- The step simulation (ideal diodes with a fixed drop, capacitor charging instantly and discharging through the load) was checked in the tests against an exact Python solution (scipy brentq and quad). Peak voltages, loads and capacitors are example values.
- Drawings are fibub's own. Nothing you enter is stored or sent anywhere.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.