Voltage-To-Freq

Discussion in 'The Projects Forum' started by rafaello, Mar 17, 2013.

  1. rafaello

    Thread Starter New Member

    Mar 10, 2013
    5
    0
    Hello,


    I'm looking for Voltage-To-Frequency converter circuit including only analog components. (passive, op-amps, transistors).

    Output signal can be either 50% duty cycle square wave or 90%+ duty cycle (low voltage only during capicator discharge - preferred!). Max. 40kHz.


    I've found this interesting schematic:

    http://circuits.linear.com/img/435_circuit_1.jpg

    But I'm not sure it will work. In my simulation (LTSpice) the transistor is in cut-off all the time. Capicator (op-amp V-, 0,1uF) discharges through the polystyrene capicator...

    Please, help me with this one, or maybe You know some other circuits? Thank you.
     
  2. ifixit

    Distinguished Member

    Nov 20, 2008
    638
    108
    What frequency range do you need to cover with what voltage range?

    Thanks,
    Ifixit
     
  3. rafaello

    Thread Starter New Member

    Mar 10, 2013
    5
    0
    ~0V to 10V input voltage
    and
    ~0Hz to 10kHz output freq.

    Would be perfect.
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,001
    3,229
    Post you .asc file so we can run your simulation.
     
  5. rafaello

    Thread Starter New Member

    Mar 10, 2013
    5
    0
    Here you go. I understand, that "0.001 (polystyrene)" means 0.001 uF.

    You can see, that it's working... but try to remove the transistor and there won't be a difference.
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    The transistor is there to prevent latchup when starting.
    Remove your UIC from the .tran statement and see what happens when the transistor is removed.
    With the transistor installed, once the circuit is operating properly, the base-emitter junction is reverse biased, so it is basically out of the circuit.
     
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