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What are the alternatives of LED Flasher/Oscillator LM3909?

Discussion in 'General Electronics Chat' started by alanzhao, Jan 23, 2004.

  1. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The minimum supply voltage for an ordinary 555 is 4.5V.
    The minimum for a Cmos 555 like an LMC555 or TLC555 is 1.5V but then it has hardly any output current and a charge-pump circuit is needed to double the voltage to light an LED.
     
  2. THESTOCKSGUY

    THESTOCKSGUY New Member

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    Lm3909

    I am looking at an inventory of +67,000 Pcs.....from 1 Company.

    Why are there alarms for scarcity and alternatives to this chip ?

    Ebay Scalpers have a $2.99 + $1.99SH each.

    Google: CHINA ELECTRONICS LM3909

    Paul T. Knisely (Seattle) 4258065209
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    A Cmos 555 does not double the supply voltage like the LM3909 does so it needs a 3V battery instead of a 1.5V battery.
    The Cmos 555 has an extremely low output current when its supply voltage is low but the LM3909 supplies plenty of current to the LED when its supply voltage is from 1.0V to 1.5V.
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The minimum supply voltage for an ordinary 555 is 4.5V. A Cmos 555 works with a supply as low as 1.5V but its output current is extremely low and it does not double the voltage like an LM3909.
     
  6. BADFLOPPY

    BADFLOPPY New Member

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    Better you use a transistorised astable multivibrator with NPN & PNP transistor and a POT in series with feedback Capacitor. This is the cheapest circuit and the simplest one.
    [​IMG]

    Use left npn biasing resistor as 1m, pnp collector res 1 k, feedback capacitor (1-10uf) & pot 220e to 1k. Use led biasing resistor as per supply & led current.
    The wrong supply and the supply node is emitter of PNP transistor. Please excuse me as I draw in hurry.
     
    Last edited: Nov 16, 2009
  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Bill bowden has almost the same circuit except it has a voltage doubler so it works from a single 1.5V battery cell:
     

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