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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

    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?

    Any other simple circuit ideas welcome
  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.


    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:
    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
  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.

  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
  7. Brian

    Brian Guest

    Another approach is to use a switching converter IC, such as the MC34063A.
    Take a look at the drawing at

  8. Det var smuk og solrig dag da royalmp2001 skrev
    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.

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