Bridge rectifier and smoothing
A DB107 bridge rectifier turns 12 V AC into DC, and a 470 uF capacitor smooths it: about 10.6 V with a 0.2 V ripple at 100 Hz. There is no microcontroller in it: the simulator solves the 6 parts as a circuit, so it runs the moment you press Run, and nothing needs compiling.
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Beginner About 20 minutes to build and run. Runs in your browser. Free, and no account needed.
What you'll learn
- How a diode bridge turns AC into DC
- Why full wave rectification doubles the ripple frequency
- A smoothing capacitor holds the voltage between peaks
- Ripple shrinks with a bigger capacitor or a lighter load
- Reading a scope trace and a multimeter together
- Difficulty: Beginner
- Time: About 20 minutes
- Parts: 3
How it works
This circuit has no code. A signal generator makes 12 V peak AC, which swings positive and negative. A DB107 bridge rectifier holds four diodes that flip the negative half over, so the output only ever pushes one way.
Two diodes conduct on each half cycle, and each costs about 0.7 V. So the DC output peaks at about 12 minus 1.4, or 10.6 V. A 470 uF capacitor then fills the gaps between peaks while a 1k resistor drains it as a load.
The oscilloscope shows the result. CH1 reads the DC output with a small ripple of about 0.2 V at 100 Hz, twice the 50 Hz input, which is what full wave means. CH2 shows the generator itself.
Parts list
3 parts, plus the jumper wires and 3 bench instruments. Every one is in the editor's parts bin.
- 1 × Signal generator
- 1 × Bridge rectifier, DB107
- 1 × Capacitor, 470 µF
- 1 × Resistor, 1k ΩIn Starter Kit, Claw Machine Kit, Halloween Prop Kit.
- 1 × Oscilloscope
- 1 × Multimeter
Wiring table
Every connection, pin by pin, read from the circuit itself. Each row joins the pin on the left to the pin on the right, by a jumper wire or a breadboard strip.
| Part and pin | Connects to |
|---|---|
| Bridge rectifier, DB107 pin AC1 | Signal generator pin OUT |
| Oscilloscope pin CH2 | Signal generator pin OUT |
| Signal generator pin GND | Ground |
| Bridge rectifier, DB107 pin AC2 | Ground |
| Capacitor, 470 µF pin 1 | Bridge rectifier, DB107 pin DC+ |
| Resistor, 1k Ω pin 1 | Bridge rectifier, DB107 pin DC+ |
| Oscilloscope pin CH1 | Bridge rectifier, DB107 pin DC+ |
| Multimeter pin V | Bridge rectifier, DB107 pin DC+ |
| Bridge rectifier, DB107 pin DC- | Ground |
| Capacitor, 470 µF pin 2 | Ground |
| Resistor, 1k Ω pin 2 | Ground |
| Oscilloscope pin GND | Ground |
| Multimeter pin COM | Ground |
The notes that come with it
There is no microcontroller in this one, so nothing is compiled: the simulator solves the circuit itself. The file in the editor is the notes that come with it.
// A full-wave bridge rectifier with a smoothing capacitor.
//
// The generator is 12 V peak AC at 50 Hz. Every half cycle two of the
// bridge's four diodes conduct, so DC+ climbs to the peak less two diode
// drops: 12 - 2 x 0.7 = about 10.6 V. Between peaks the 470 uF capacitor
// carries the 1k load, and sags by
//
// ripple = I / (2 f C) = 0.0106 / (2 x 50 x 470e-6) = about 0.23 V
//
// The scope's CH1 shows that ripple at twice the mains frequency, 100 Hz,
// which is what full wave means. CH2 is the generator's output measured from
// DC-: on its positive half it sits a diode drop above DC+, on its negative
// half a diode drop below ground, because the generator floats. Things to try: take the capacitor out and watch the
// humps come back, or make it 47 uF and the ripple grows ten times.
Troubleshooting
The usual mistakes with this circuit, and the fix for each.
- The output is a row of humps and not steady DC This project
Check that the 470 uF capacitor is connected from DC+ to ground. Without it you see the raw rectified waveform. - No output at all This project
Make sure the generator ground joins the AC2 pin and DC- is grounded, so the bridge has a complete path. - The circuit under test shows clipped or distorted signals. Signal generator
A sine swinging below zero can exceed what an input allows. Add a DC offset or bias so the signal stays inside the supply range of the part. - Measurements are off or noisy. Signal generator
Join the generator's ground to the circuit ground. Keep amplitude and frequency within what the connected parts can handle. - The output voltage is lower than expected. Bridge rectifier
Two diodes conduct at a time, so you lose about 1.4 V from the AC peak. The DC voltage is the peak (RMS times 1.41) minus that. - The output is rippled, or the part is wired wrong. Bridge rectifier
Add a smoothing capacitor across the DC output, matched to the load. The two AC pins have no polarity, and the plus and minus pins do, so mind the labels. - An electrolytic capacitor heats up, bulges or pops. Capacitor
Electrolytics have a polarity. The stripe marks the negative leg, which goes toward ground. Also keep the voltage under the rated value, such as 10 V or 16 V. - An RC circuit charges much slower or faster than expected. Capacitor
The time constant is R times C. A 10 k resistor with a 100 uF capacitor gives 1 second, and about 5 seconds to charge fully. Check that you read the value on the part right.
Change it and keep it
Open it in the editor, change the circuit or the code, and keep your version in a free account.