power supply using bridge rectifier

Thread Starter


Joined Mar 15, 2010
I have a 220/48 v ac transformer and i want to use it to get 24 v which source 3 A at least with bridge rectifier to give 24 v , 3 A dc , should i use another 48/ 24 v ac or there is any thing else to down the voltage to 24 before rectifier ?


Joined Feb 24, 2006
AC voltages are RMS (Root Mean Square). A bridge rectifier will have a DC output roughly equal to √2 * RMS_Voltage. In your case:

48 VAC(RMS)*√2 ≈ 67.8 VDC

To regulate this down to 24 volts will be a challenge.


Joined Mar 30, 2015
Get a transformer better suited for the desired output voltage. Your output plus a few volts for regulator drop out, and a couple volts for diode drop and ripple would be around 29VDC. A transformer secondary around 20VAC would minimize power dissipation.


Joined Aug 1, 2013
As noted in post #3, the output of the bridge/filter capacitor will be about 65 Vdc after figuring in the bridge diodes forward voltage drops. You can regulate this to 24 Vdc with a simple circuit, but the circuit will dissipate over 100 W, requiring a large heatsink plus a fan. A much more efficient approach is to use a switching regulator, but this is a more complex circuit. If you don't want to build one, you can buy them on ebay for less than $20.