555 Timer pin 3 help

Discussion in 'General Electronics Chat' started by MnobodyM, Nov 5, 2010.

  1. MnobodyM

    Thread Starter New Member

    Nov 5, 2010
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    0
    Hello
    please help how to get down voltage from 555 timer pin 3 down from 0.9v to 0v help please :confused:
    input voltage is 13v
     
    Last edited: Nov 5, 2010
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    0 V at what load? Use 555-3 to drive a reed relay with mercury wetted contacts to give near 0 V up to relays rating. Or use power FET with inversion from 555 to give around 50 m ohms.
     
    Last edited: Nov 5, 2010
  3. iONic

    AAC Fanatic!

    Nov 16, 2007
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    a diode maybe?
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Are you talking about a conventional 555 or a CMOS 555?

    Pin 3 on a convention 555 will reach 0V easily. If not you have something dramatically wrong with your circuit.
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I agree with Bill. There could be something wrong.
    Post your schematic to see if there is anything wrong with it.

    Bertus
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    The output saturation voltage of the 555 timer's pin 3 will increase with the amount of current you're trying to sink.

    At light loads, it's nearly 0v. As you approach 200mA sink current, the saturation voltage increases. If you attempt to sink more than 200mA, the saturation voltage will become excessive.
     
  7. Wendy

    Moderator

    Mar 24, 2008
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    I was thinking about that while driving. I suspect the OP is trying for more than 0.1A, it seems to be a common mistake. 200ma (the absolute max, you should not try for more than half that) is plenty of current for most applications, if you need more you need transistor drivers.

    If you have pushed this chip too hard forcing it beyond its limits it is probably blown. They can only take so much.
     
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