LearnTronics
Diode Rectifier and Filter Capacitor
Recipe #5 — diode rectifier and smoothing capacitor
A diode and capacitor can turn an AC waveform into a simple DC supply for a light load.
Safety: this example begins at an already-isolated low-voltage AC source, such as a transformer secondary. It is intentionally not a mains-wiring lesson.
Follow the current: AC rises positive → D1 conducts → C1 charges → AC falls → D1 stops conducting → C1 supplies the load for a short time → next positive peak recharges C1.
What the capacitor changes
Without C1, the output is a series of one-polarity pulses. With C1, the voltage falls more slowly between peaks, producing smoother DC with some remaining ripple.
Another way to think of the capacitor
It is like a small reservoir. The diode refills it near waveform peaks, and the load drains it between peaks.
More load means more ripple
A heavier load removes charge from the capacitor more quickly. A larger capacitor generally reduces ripple, but it also changes charging current and places more stress on the rectifier and source. Real power supplies must consider those current ratings.