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Rung 7 · See change over time

Rectify and smooth AC

Build a bridge rectifier, then use a capacitor to reduce the valleys in its output.

intermediate40 minutes0 of 4 stages explored
Open blank FalstadReference options
A twelve volt peak alternating source feeding a four-diode bridge, smoothing capacitor, and one kiloohm load.
12 volt peak AC source -> four-diode bridge -> 100 microfarad capacitor in parallel with 1 kiloohm load

Knowledge this exercise builds on

Lesson 5: DC vs ACLesson 7: Power and Energy: Watts, Watt-hours, and Electric Bills

Practice loop

Try each step before revealing its answer.

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ComponentsSee the parts and values before you start.
  • One 12 V peak, 50 Hz AC voltage source
  • Four diodes
  • One 1 kΩ load resistor
  • One 100 µF capacitor
  • Input and output scopes
PredictCommit to an expected result before running the circuit.

Predict how a bridge uses both AC half-cycles. Then predict what the capacitor does near each waveform peak and valley.

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The bridge redirects both AC half-cycles so load current keeps one direction. A 50 Hz source therefore produces 100 Hz rectified pulses. The capacitor charges near each peak and supplies part of the load as the rectified voltage falls between peaks.

BuildWire the circuit yourself from a blank canvas.

Build the bridge first without the capacitor. Confirm full-wave pulsing output, then place the capacitor in parallel with the load.

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Orient the four diodes so either source polarity drives current through the load in the same direction. Connect the 100 µF capacitor directly across the load, with its positive side on the bridge’s positive output.

MeasureSee what to inspect, compare, and change.

Measure output frequency without the capacitor. Then compare output ripple with 47 µF, 100 µF, and 470 µF. Lower the load resistance and record what changes.

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The unsmoothed bridge output pulses at 100 Hz. Increasing capacitance from 47 µF to 470 µF reduces the fall between peaks, so ripple becomes smaller. Lowering load resistance draws more current and discharges the capacitor faster, so ripple increases.

ExplainConnect the observation back to your model.

Explain why the capacitor charges near peaks, supplies part of the load between peaks, and cannot produce perfectly flat DC by itself.

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Rectification controls direction. Smoothing shifts stored energy through the short gaps between rectified peaks. Regulation would be a later stage.

The capacitor charges only when bridge voltage rises above capacitor voltage. Between peaks, it releases stored electric-field energy into the load, so its voltage must fall somewhat. That repeating fall is ripple.

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Safety boundary

This is a low-voltage educational model.

Do not translate it into mains construction, household wiring, battery-pack work, or real protection settings. Real electrical systems need rated components, proper protection, test equipment, and qualified safety judgment.