power supply using bridge rectifier

Discussion in 'General Electronics Chat' started by mah, Jan 2, 2016.

  1. mah

    Thread Starter Active Member

    Mar 15, 2010
    276
    2
    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 ?
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,500
    2,366
    For 24vdc you would need ~17vac.
    Take turns off?
    Max.
     
  3. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    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.
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
    3,211
    619
    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.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,515
    1,246
    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.

    ak
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,766
    928
    You don't mention where your home is, but you could use 110 VAC to get 24 volts from your 220/48 xformer.
     
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