Power supply help!!

Discussion in 'Homework Help' started by imfaizzi, Oct 18, 2008.

  1. imfaizzi

    Thread Starter Member

    Oct 11, 2008
    20
    0
    hi

    Will a 5V power supply enable a 3V circuit of a bell?

    I've designed my Power supply using a 12V step-down transformer and 7805 chip which gives an output voltage of 5V whereas the circuit requires 3V to get operated.

    Wiil it??
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    A 3V bell might smoke and burn if you feed it 5V.
    Or the current might be too high for the 7805 and it will get too hot and shut down.
     
  3. imfaizzi

    Thread Starter Member

    Oct 11, 2008
    20
    0
    then whats the solution??? :confused:
     
  4. chrissyp

    Active Member

    Aug 25, 2008
    82
    10
    Hi
    Check the current of the bell and if it is within the spec of a variable voltage reg ,use one of those instead of a fixed reg.
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    Depending upon how you derive your 12v supply you have enough voltage to arrange an asymmetric ± supply or even a second small negative one. You can use this to return the reference pin of the 7805 to the negative rail instead of zero. With suitable choice of rails you can arrange the output of the regulator to be 3 volts above zero, but 5 volts above the negative rail.
     
  6. imfaizzi

    Thread Starter Member

    Oct 11, 2008
    20
    0
    can I use any other component besides "7805", in the first place, to restrict my output to 3V? Is there any IC available of such kind?
     
  7. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    The L200 will go down to 2.5 volts.
     
  8. chrissyp

    Active Member

    Aug 25, 2008
    82
    10
    I would prefer to use an LM117 although it is 1.5a it will drop as low as 1.2v -36v. My ST databook says L200 min voltage is 2.85v , thats a bit too close for comfort to 3v.
     
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