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Flashing LEDs - 9V

Discussion in 'Electronic Basics' started by Neil, Sep 3, 2006.

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  1. Neil

    Neil Guest


    I want to build a very simple circuit to alternately flash 2 high power
    LEDs - the sort you get in cycle lights. I have seen numerous
    circuits, either using a bistable oscilator with 2 transistors, or a
    555 IC, however, these all seem to run off 3 or 5v, and I would like to
    run this at 9v (I have a 9v supply where I want the LEDs). I would be
    grateful if someone could point me in the right direction as to how I
    might achieve this.


  2. The 555 will work at 9V, even 12 or 15V. So will "non-logic-level"
    power MOSFETs, such as ones by International Rectifier not specifically
    claimed to be "logic level". The "logic level" ones are also good for 9V
    as long as you can be sure the voltage never exceeds 10V. You can use a
    555 to switch MOSFETs.
    Also consider 4000B series logic - good for all voltages 4.5 to 15
    volts. 74C series logic is also good for at least the 4.5-12V range,
    maybe 15.

    Another consideration: Use 5V logic powered by a 5V regulator (7805 or
    the like) and have final logic outpouts drive gates of "logic level"
    power MOSFETs. The MOSFETs can still switch loads at voltages up to their
    drain voltage limits, 20 volts and up.

    - Don Klipstein ()
  3. ehsjr

    ehsjr Guest

    A 555 will do it. See:
    That's one of many urls that show flashing LED circuits.
    If the "high power" LEDs need more than about 150 mA,
    then you'll want to add transistor drivers, otherwise
    the 555 can do it correctly.

  4. default

    default Guest

    That first circuit, Eccles-Jordan multivibrator, will alternately
    switch incandescent lamps directly. 2N2102 will switch about an amp
    in that circuit, 2N3904 is good for 200 ma.

    Better than a 555 if you have to add transistors to switch the load
    (and don't need to vary the flash rate easily)
  5. "Bistable oscillator" sounds like a contradiction. Guess you mean astable
    (sometimes written as a-stable). This type of oscillators were ever build
    using electonic tubes, powered by up to 200V. Maybe more. There's no reason
    to use a 5V supply for transistorized oscillators. You can still use even
    200V, choosing the right transistors of course. So 9V will not be a problem.
    That's not to say you can apply 9V to a circuit designed to be used at 5V.
    Currents may rise too high and blow the transistors. Actual components
    depends on the current required by the LEDs and the on/off timing (duty
    cycle). A 0.1s flash once an hour will not be easy to build this way.

    petrus bitbyter
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