24 to 12 volt circuits

Discussion in 'General Electronics Chat' started by MI Installs, Jul 26, 2007.

  1. MI Installs

    Thread Starter New Member

    Jul 26, 2007
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    Installing equipment on off road machinery that is 24 volts. I would like to get my power source from the ignition switch. The device only draws 50mA @ full power (12 Volts) and I have a limited amount of space to work with.:confused:
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,178
    1,799
    For 50 mA @ 12V you just might be able to use a 7812 in a TO-220 package. At 600 mW it will get just a bit warm.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    That should work OK - but you should also use some capacitors on the input and output to prevent oscillations, because it's a given that the wire length is going to be at least a foot either way. Use an 0.33 uF cap to ground on the input, and a 0.1 uF cap to ground on the output, both with a 30v rating. Otherwise, the oscillations could lead to some mighty high voltage spikes.

    A Texas Instruments uA7812C has a rated output of up to 1.5A (with proper heat sinking, of course) with a minimum Vin of 14.5 and max Vin of 30. If you get it too warm, it'll let you know by shutting down (thermal overload protection). A National LM7812 or other xx7812 would work just the same.
     
  4. MI Installs

    Thread Starter New Member

    Jul 26, 2007
    2
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    Thanks for the responses

    Would it be possible to get a drawing of this circuit?
     
  5. John Luciani

    Active Member

    Apr 3, 2007
    477
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    There are drawings in the LM7812 datasheet.

    (* jcl *)
     
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