Created by
Created February 04, 2012
Last modified February 04, 2012
Tags ac-to-dc   bridge-rectifier   power-supply   transformer  


An AC source, a transformer, and a bridge rectifier (full diode bridge) can turn an AC "wall" source into a usable DC source for low-voltage electronics.


At the core of many "wall wart" power adapters (the adapters that convert from high voltage 50/60Hz AC wall power to the low-voltage DC that many electronic devices need) are a few simple ingredients: a step-down transformer, a bridge rectifier (composed of four diodes), and a filter capacitor.

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.

Adjusting the load and filtering capacitor

How much "ripple" do you see in the output voltage? Adjust the resistance of R_LOAD and see how the discharge changes. Or, adjust the capacitor value C1 to provide more or less filtering.

Advanced: more filtering

Depending on the load, you can use more resistors, capacitors, and inductors to build a higher-order filter to reduce the voltage ripple substantially!

Or, try using this circuit in combination with a linear voltage regulator to provide a regulated output voltage. How much power does the regulator waste?

See also

Diode half-wave rectifier:

Diode full-wave rectifier:


I'm pretty novice at this, but can you please explain why you need the transformer? The circuit works fine with a voltage regulator at the output, L7805 for example.

by jwdupuy313
August 30, 2012

@jwdupuy313 The transformer provides both isolation for safety as well as a decrease in the AC voltage from the line level to near the final DC level. Also see

by mrobbins
August 30, 2012

the problem with a more complex filter net work is its "passive" which means loss Id try unloading your circuit a bit "c2"to1000 uf and "r1" to 470

by leonriege
February 05, 2013

So in a control circuit, if input voltage is only 24v to 36v AC(as opposed to 120V), and amperage is very limited(millivolts), is it safe to use only the voltage regulator? I would like to avoid the transformer if possible.

by jwdupuy313
February 06, 2013

Its been some time since I work with them but I think the LM7805 in the "to 220"package( 5 amp } has a max input of 40 volts check the data sheet you say 24 to 30 volts? how much current? from your source? we use xfmrs for several reasons the least of which is saftey if your pwr requirements are as small as you say get a 50va or whatever you need surplus from "all electronics"

by leonriege
February 07, 2013

Leave a Comment

Please sign in or create an account to comment.

Revision History

Only the circuit's creator can access stored revision history.