triangle waveform and sweep generator

Discussion in 'The Projects Forum' started by badbaud, May 22, 2012.

  1. badbaud

    Thread Starter Member

    Mar 5, 2009
    26
    0
    I have found plenty of triangle waveform generator circuits but they can't do any actual work.

    The waveforms are cute to look on a scope but they float somewhere between + and ground. Not from ground to + and back.

    I have a 12V DC 3 Amp load, the circuit is potted so I can't get inside it to modify the original circuit.

    I need to sweep this load's power from all of the way on to all of the way off
    and back again. Frequency adjusted from 10 Hz down to .1Hz with a pot.

    Needing constant current is not an issue.

    Adjusting the high voltage limit and low voltage limit of the sweep is necessary.

    Attached, I hope, is the basic sweep circuit I have started with.

    It's output hangs close to the 12V rail and is around 4 Volts peak to peak and I can't remove the positive voltage offset to get a signal I could drive a higher current bipolar transistor with to control the load without affecting the sweep shape.

    Any help would be appreciated.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,766
    2,536
    The problem is rail to rail is usually not practical, as the vast majority of electronic devices (including transistors) do not do rail to rail well. This is especially true if you are after good linearity characteristics. It is more important to have a fixed dependable voltage on a P-P rating.

    [​IMG]

    This circuit does a reliable 1/3 to 2/3 Vcc. You want rail to rail? Find an op amp or amp that can to it and have a gain of 3. The odds are you won't have much luck. You need a second power supply that is independent of the 1st, so you can hit the voltage specs you want.
     
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