Rectifier and Smoother

A diode keeps only the positive half of an AC signal, and a capacitor smooths it toward DC.

Intermediate
Analog Electronics
6 parts

Opens in your browser with the parts, wiring and code already in place. Press Run to watch it work, then change anything you like.

How it works

The function generator makes a 100 hertz sine wave that swings 5 volts above and below zero, like a small AC supply. A single diode in the path only conducts when the input is higher than the output, so the negative half is blocked completely and the positive half passes with about 0.6 volts lost across the diode. That is a half-wave rectifier, and its output is a series of positive humps with gaps between them.

A 10 microfarad capacitor and a 1 kilohm load sit after the diode. The capacitor charges up to each peak and then supplies the load while the input falls away, which fills in most of each gap. What is left is a small ripple, falling as the load draws charge and jumping as the next peak recharges it. The oscilloscope shows the raw input in yellow and the smoothed output in blue. This is the first stage of nearly every power supply.

Parts

Function Generator
Diode
Resistor
Capacitor
GND
Oscilloscope

Wiring

Function Generator OUT → Diode Anode
Diode Cathode → Resistor A
Diode Cathode → Capacitor +
Resistor B → GND
Capacitor - → GND
Function Generator GND → GND
Oscilloscope CH1 → Function Generator OUT
Oscilloscope CH2 → Diode Cathode
Oscilloscope GND → GND

Arduino code

// Rectifier and Smoother
// Press Run: channel 1 is the AC input, channel 2 the rectified, smoothed output.
// There is no sketch to write: this is a circuit, so there is nothing for code to do.
void setup() {
}

void loop() {
}

Try changing it

Select the capacitor and change its capacitance to 100. The ripple shrinks a lot, because a larger capacitor holds more charge between peaks.
Change the load resistor to 220 and the ripple grows, because a heavier load drains the capacitor faster.
Change the generator frequency to 400 and the ripple falls again, as the peaks come four times as often.

Open this circuit and run it

Next challenge

Op-Amp AmplifierAn op-amp with two resistors in its feedback loop multiplies a small signal by a precise…