AC to variable DC power supply please

Discussion in 'General Electronics Chat' started by Gunz1159, Oct 15, 2010.

  1. Gunz1159

    Thread Starter New Member

    Oct 12, 2010
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    Hi,

    Can any one build me a regulated power supply variable from 0v to 12v Dc from a 240v AC. Please ? ? ? ? ? ? ?
     
  2. bertus

    Administrator

    Apr 5, 2008
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  3. tom66

    Senior Member

    May 9, 2009
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    So you want us to do your homework?

    Here is one example circuit you could try.

    http://www.electronics-project-design.com/VariableDCPowerSupply.html

    Remember to use an isolated power supply (like a transformer as shown in the circuit) to get the unregulated DC.

    Also remember that as this is a linear power supply to drop the voltage heat is dissipated in the regulator. For that reason for current levels over 100mA you MUST heatsink the regulator.
     
  4. Audioguru

    New Member

    Dec 20, 2007
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    The LM317 has a minimum output voltage of 1.25V, not 0V.
    If its load current is less than 10mA, by using 330 ohms instead of 120 ohms then its output voltage might rise.
     
  5. tom66

    Senior Member

    May 9, 2009
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    That is a good point.

    To get zero volts out you can turn the power supply off, but if you need to vary the voltage in that range of 0-1.25V then another circuit will need to be built.

    The problem is it is difficult for a regulator to go below its reference voltage. But it is possible if you have an op-amp as a linear regulator (with appropriate pass transistor) and adjustable reference.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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