Created by
Created November 13, 2011
Last modified May 17, 2012
Tags ac-to-dc   bridge-rectifier   diode   time-constant  

Summary

Four diodes (a "bridge rectifier") plus a capacitor can be used to rectify AC into DC, with conduction over most of the the input power cycle.


Description

Vsrc and Rsrc represent a 12V, 60V voltage output, like you might find at the output of a small power line transformer.

D1, D2, D3, and D4 are each a 1N4007 diode. They're set up as a full-wave bridge rectifier. When Vsrc is positive, D1 and D2 conduct to charge capacitor C1. When Vsrc is negative, D3 and D4 conduct to charge C1.

C1 is the capacitor that we rely on to store and release energy for much of the voltage cycle.

Rload represents our load circuit -- perhaps it's a linear voltage regulator, or maybe just a simple resistive load like a light bulb.

A few things to try in CircuitLab

Load the simulation by clicking "Open in editor" above, and then click "Simulate" at the bottom. Run a time domain simulation.

Redefining ground

This kind of circuit can be hard to think about because, if we define ground to be at the negative end of Vsrc as we do here, both sides of the output of the bridge rectifier are moving with respect to ground. However, the difference between then stays relatively constant thanks to C1.

You can try moving the ground terminal to be at the bottom end of C1 -- see what happens! This can make it easier to look at the output waveforms, but in reality the same thing is happening. The only change is the definition of the zero voltage reference point.

Note that you don't want to put grounds in both places (and in real life, you don't want to build this circuit with those two points connected!). That would defeat the full-rectifier action.

Output voltage ripple

Take a look at how much the output voltage wiggles even though it's supposed to be DC! You can try making C1 bigger to reduce the ripple, but in the real world that's more expensive.

Try changing the load Rload, and see how this alters the output voltage waveform.

You can also replace Rload with a current source, which might better represent how something like a linear voltage regulator might look to this circuit.

See also

Diode half-wave rectifier:

AC Power Supply (Transformer and Bridge Rectifier):


Comments

Very nice. I used this to learn how this circuit works - especially related to the question of what is ground. I then used it to teach another person in my office.

thanks!

mark

by mjkuwp94
July 20, 2012

please tell me the common equation for the bridge rectifier circuit

by saswati
December 14, 2012

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