Easy question!

Discussion in 'General Electronics Chat' started by Jeffrey Jay, Nov 1, 2006.

  1. Jeffrey Jay

    Thread Starter New Member

    Nov 1, 2006
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    0
    Hey guys

    I have a small device that requires 9vdc and all I have present (truck trailer) is 12 vdc. What do I need to convert? Load is less than two amps or so.

    Thanks!! :confused:
     
  2. Papabravo

    Expert

    Feb 24, 2006
    9,900
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    Some linear regulators of the 78xx10 Variety and some schottky diodes, and some capacitors should do the trick. How were you planning to fabricate the circuit?
     
  3. Jeffrey Jay

    Thread Starter New Member

    Nov 1, 2006
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    0
    Sounds pretty deep for me...I was thinking just selecting a resistor to drop a couple three volts...Do you think this is something I could purchase pre assembled? Seems like it should'nt be too hard??

    Thanks for your assistance! -Jeff
     
  4. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    You can get a device from a truck stop that will convert 12vdc to whatever you want and it comes with adaptors. Flying J has them.
     
  5. Jeffrey Jay

    Thread Starter New Member

    Nov 1, 2006
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    0
    Oh, cool! Thanks!! -Jeff
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    The problem is that 3 Volts = (12 V - 9V) times 2 Amps = 6 Watts. That will be a pretty expensive resistor to say nothing of the fact that at low current the drop will be less than 3 Volts.

    Where do people get this quaint notion that a dropping resistor will not dissipate potnetially large amounts of power.
     
  7. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    And with a resistor of course, if the load current drops, the voltage will rise.

    A 7809 will regulate to 9 volts at 1.5 amps.

    5 diodes in series (1N5408 or similar) will drop 3 volts across them.... but if your 12 volts rises to 14 volts..(as in when battery fully charged) then that will mean there is now 11 volts out.
     
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