555 Control Voltage

Discussion in 'General Electronics Chat' started by Razor Concepts, May 6, 2011.

  1. Razor Concepts

    Thread Starter Active Member

    Oct 7, 2008
    212
    1
    Say a 555 is set up in astable mode such as this:
    [​IMG]

    The frequency of that, with control voltage at the standard 2/3 V, is this:
    [​IMG]

    Now, what if the control voltage isn't 2/3V? What would the new frequency formula be?

    TIA!
     
  2. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The datasheet shows that the frequency changes and the duty-cycle of the output pulses also changes. It is called Pulse-Position-Modulation.

    There is no formula but you might be able to figure it out.
     
  3. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    It is pure RC math, available in every text book. Since Pin 5 is connected to the voltage set points you can easily vary off the 2/3 setup point.

    It is a function of natural logs, which you know since you showed an atypical formula for this oscillator.
     
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