Please help with my power supply project

Discussion in 'The Projects Forum' started by DanAir, Jan 31, 2007.

  1. DanAir

    Thread Starter New Member

    Jan 31, 2007
    I'm going to build a power supply for my tinkering projects using an existing 120/240 VAC to 12/24 VAC transformer rated at 48VA, and will use the 12V option. My week of reading has not answered all of my questions, so I need to ask an expert(s).

    The bridge rectifiers I'm looking at on have spade terminals:
    Mouser part numbers: 512-GBPC12005 12amp 50v
    512-GBPC36005 35amp 50v
    512-GBPC35004 35amp 400v
    The difference in cost is very small, so would a part with a higher rating be a better choice, considering a larger transformer could be used in the future?
    Is current loss a factor in rectifiers, thus making a minimally rated part the only reasonable choice? Are all of these too big?

    Reading has suggested a capacitor connected across the DC output of the bridge rectifier for smoothing out the AC ripple. Is this correct, and if so, what size capacitor would be required?

    Any advice will be greatly appreciated !!!

  2. Mazilla

    New Member

    Jan 31, 2007
    Hello DanAir.

    If I have not misunderstood you, the power supply, you are designing, will be very simple: transformer, bridge and capacitor. It really will be enough for device which doesn’t require high quality of power/voltage.
    Any of listed bridges can be used in circuit like yours. But I recommend use that part, with higher maximum reverse voltage.
    Probably it is a good idea to use voltage stabilizer to increase the quality of your circuit’s power supply.

    About capacitor: it is very important part of power supply circuits.
    The higher capacitance, in this case, is preferable. But to safe you money you should calculate that one using maximum voltage pulsing parameter of load.

    Best regards,
  3. DanAir

    Thread Starter New Member

    Jan 31, 2007
    Thanks for the is a very simple circuit. You recommend the 400volt, 35 amp bridge, correct? This transformer is 48 va, but I may use a larger one in the future with this same rectifier. That is OK?

    As far as the capacitor, I don't know how to calculate its value...the circuit initially will be loaded less than 4 amps at 12 volts. What value and type of capacitor should I use?

    Thanks Again,
  4. dragan733

    Senior Member

    Dec 12, 2004
    Why to use 35A bridge for 4A? 35A bridge is with big dimensions.

    About the capacitor, use 1000uF/1A. Therefore for 4A use 4000uF. I.e. take 6800uF.

    About the transformer. Yes, you can use larger power of the transformer, but from other side that is bigger dimensions, weight and price of the transformer
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
    If cost is no barrier then consider size and mounting. With those types of diodes you an use them with lower voltage and current but you can't use a little one for bigger things. I'd consider the bigger bridge. The nice thing about the larger ones is they have a higher opps value.
  6. Gadget

    Distinguished Member

    Jan 10, 2006
    And of course a good current rating IS desirable especially if a large smoothing capacitor is used due to the Peak currents involved.
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    C >= 0.7(I)/Er(f) Where Er is the maximum allowable ripple voltage.