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what size resistor to reduce 4.5v to 3v?

Discussion in 'Misc Electronics' started by BIGSteve, Jan 26, 2005.

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  1. BIGSteve

    BIGSteve Guest

    got an old portable cd player needs 3vdc got a 4.5vdc car adapter need
    to make the 2 work together. So how do i reduce the 4.5v to 3v can i
    use a resistor? what size?
    thanks
     
  2. Jerry G.

    Jerry G. Guest

    Resistors in the proper configuration can work as a voltage divider. The
    voltage across the load is depended on the applied voltage, current, the
    value of the resistance in series, and also the load resistance.

    A simple series resistor, or a divider circuit is not accurate, unless the
    current pull from the load is very constant, and precise. To run your CD
    player you should get the proper regulated 3 VDC supply.

    If your CD player uses less than 1 amp, you can put two of 1N4007 rectifier
    diodes in series with the plus side of the voltage feed going to the player.
    The cathode sides (side with the silver ring) of the diodes must face the
    player's plus input. Each of these diodes will make a loss of about 0.68 to
    0.72 Volts. This should get the 4.5 Volts down to be close enough. There
    will not be very much added instability, because the voltage drop through
    these diodes is very stable and constant.


    --

    Jerry G.
    =====

    got an old portable cd player needs 3vdc got a 4.5vdc car adapter need
    to make the 2 work together. So how do i reduce the 4.5v to 3v can i
    use a resistor? what size?
    thanks
     
  3. CWatters

    CWatters Guest

    A single resistor is unlikely to work because the current drawn by the cd
    player isn't constant.

    You could probably use a "low drop out 3V regulator" and some capacitors but
    it might be worth looking for a cell phone adaptor that produces 3V. The
    voltage isn't usually written on the box - look for a label on the actual
    adaptor somewhere.
     
  4. Jamie

    Jamie Guest

    i would say that you could experiment with using 2 or 3 silicone diodes
    in series. each one will drop the voltage aprox. to 0.5..0.6 voltage.
    it mite be better to simply place a safe load on the end of the string
    and then measuring it with a DVM (volt meter) to verify that its close
    before connecting to the CD unit.
     
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