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Bridge rectifiers

Discussion in 'General Electronics Discussion' started by Heeran, Jul 3, 2013.

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  1. Heeran

    Heeran

    64
    0
    Nov 13, 2012
    Hi
    I am building a circuit and I have 230 ac volts coming in from y house plug. I need an output of 0 - 15 volts and a maximum output amp of 20amp. Please assist me as to what kind if four pin PCB transformer rating I require as well as what kind of bridge rectifier. I possible, could you provide me with a drawing and will I need to add a capacitor across the output poles of the bridge rectifier.
    Thanks
     
  2. davenn

    davenn Moderator

    13,654
    1,888
    Sep 5, 2009
    Heeran

    greetings

    I doubt you will find a PCB mount transformer that will be capable of 20Amps. Its going to be a reasonably big and heavy transformer. PCB mount transformers would be up to ~ 2 Amp max

    [​IMG]

    cheers
    Dave
     

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  3. Heeran

    Heeran

    64
    0
    Nov 13, 2012
    Hi
    Thanks a lot for your help.
    If I want to protect this circuit from lighting damage, what size of TVS should I use, I require one that has two pins and is connected I parallel across the input.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
    2,780
    Jan 21, 2010
    Protection from lightning is only ever going to be partial. You can always have a stronger strike or a nearer one that will kill your device.

    Practically, presume that a direct strike *will* destroy your device. Then figure out how much protection is economically viable given the probability of the event occurring, and the potential cost of the damage.

    If the device is connected 24x7 and you're in a lightning prone area, and something expensive is connected, and it's in a location that is more likely to be close to a strike, spend more.

    Typically you would use a TVS device rated higher than your normal mains voltage and with an energy rating as high as possible given your budget. TVS devices generally have a current limit, but the energy limit (say 100J) tells you how long they can last at that current. e.g. a 1000A 100V 100J device could withstand that 1000A with 100V across it for 1/1000 of a second. that's 100J/(1000A * 100V)

    Another device to consider is a gas arrestor or a spark gap.

    In many cases these devices will suffer when called on, so depending on the energy they are asked to absorb they may be unaffected, slightly degraded, effectively destroyed, or insufficient leading to damage to the protected device. Note that eventually you get to the final state as cumulative damage leads to failure at a lower energy level.

    Another factor is that energy from a lightning strike can enter from multiple sources. It might be seen as a huge spike in mains potential, but it can also result in a potential difference between neutral and earth, or it can come in via your outputs (say from an antenna), or it can just be inductively coupled to some of your wiring.
     
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