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Simple circuit to generate 12VDC from a 9v battery?

Discussion in 'Electronic Basics' started by royalmp2001, Mar 23, 2006.

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  1. royalmp2001

    royalmp2001 Guest

    Hello everyone,
    I need to generate 12vdc from a 9v square battery, cheaply and simply,
    supplying about 20mA.
    I have looked at DC-DC convertors, but haven't come across anything
    suitable.

    I found this circuit that does something similar with a 555 timer but
    it can only supply about 12mA. Any ideas how to increase the current
    capability a little?

    http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm#5volts.gif

    Any other simple circuit ideas welcome
    Thanks
    Marius
     
  2. If you can tolerate a quarter volt of p-p ripple:
    I think that one is pretty efficient. You can tweak R1 and R2 to get
    closer to 12V, but figure about 500k-1Meg total resistance for the
    pair and that you need some 1.23V at the FB pin.

    Jon
     
  3. http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm#5volts.gif

    That circuit creates a negative voltage that is smaller than the supply.
    You need a boosting converter with a positive output. You need
    something arranged more like this:
    http://www.reconnsworld.com/power_voltdoubler.html
    This should supply enough current, just put a 1K resistor on the output
    and a 12V Zener to ground (after the resistor) to clamp the voltage at
    12V.
     
  4. Oops, I just re-read your post and you need 20mA out. Lower the 1K
    resistor I suggested to about 220 ohms and use a 1W Zener.
     
  5. Tim Williams

    Tim Williams Guest

    ^^^^
    Ah, well 9V squared is 81V, plenty to use a resistor to drop down to 12V.
    ;o)

    Tim
     
  6. kell

    kell Guest

    And if you still don't get enough current out, reduce the value of R2.
    Output current from a doubler circuit like that is proportional to
    frequency.
     
  7. Brian

    Brian Guest

    Another approach is to use a switching converter IC, such as the MC34063A.
    Take a look at the drawing at http://www.fncwired.com/9to12VoltExample/

    Brian
     
  8. Det var smuk og solrig dag da royalmp2001 skrev
    i
    sci.electronics.basics:
    How about two 1.5V batteries in series with your 9V battery. That is
    simple, and you don't throw away a lot of energy in conversions.
     
  9. John Fields

    John Fields Guest

     
  10. Deefoo

    Deefoo Guest

    This thread reminded me of a funny error from a freshly graduated
    electronics engineer that we hired some years ago. He needed something like
    7.5V from a 5V power supply, so he simply wired a resistor voltage divider
    in "reverse", ie he connected 5V to the output... Luckily I spot the error
    before he made a pcb for it.

    --DF
     
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