square wave oscillator, threshold

Discussion in 'Homework Help' started by uofmx12, Nov 9, 2011.

  1. uofmx12

    Thread Starter Member

    Mar 8, 2011
    55
    0
    Vth=Vcc*(R1/(R1+R2))

    [​IMG]

    Square wave oscillator, can someone explain the threshold equation? Also, why only R1 and R2 used?
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    R only affects the charging/discharging time of C and therefore the output frequency. It does not affect the threshold.

    R1 and R2 function as a potential divider, so that when the output of the amplifier swings from V+ to V-, the voltage on V2 swings by a smaller amount.

    When the voltage on the capacitor (V1) reaches the threshold (voltage on V2) the output switches.

    Note that the amplifier output will not usually reach V+ or V-. There will be a small voltage drop. See the amplifier data.
     
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