AC Voltage ramp from function generator

Discussion in 'General Electronics Chat' started by Ambroggio, Jun 2, 2015.

  1. Ambroggio

    Thread Starter New Member

    Jun 2, 2015
    Dear all,
    I am looking for schematics to build an AC voltage ramp generator. Basically I'm applying, from a function generator, a sinusoidal wave with 1V (effective tension) to two electrodes. But I want to reach the final amplitude (1V) in around 25min. This means I am looking for something that will allow to increase stepwise 0.2V each 5 min until 1V and stay continuously at 1V. Any suggestion?
    thanks so much
  2. ian field

    Distinguished Member

    Oct 27, 2012
    A programmable unijunction transistor has a rising ramp voltage across its timing capacitor, you can buffer that with a source-follower JFET stage and amplify it further from there if needed.

    IIRC: the 2N6027/6028 are examples of PUTs to get your search started - but you can make a substitute for that 4-layer device with a cross connected complementary pair of bipolar transistors.

    If it doesn't have to be ground referenced - you can turn the PUT circuit upside down and use a small signal SCR like the 2N5061.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    I have a function generator that can be remotely controlled from a computer program via a IEEE bus or a serial port. Any chance of borrowing something similar...

    It sounds like you have a sinosoid out function gen. You likely need to vary (modulate) its output voltage level as a function of a homebrew slow ramp generator. The modulator is likely to be more difficult than the ramp...
  4. AnalogKid

    Distinguished Member

    Aug 1, 2013
    It would help to know the sinewave frequency and the load. Going ahead anyway, one way is to attenuate the sinewave down to 0.2 V and put that into a PGA, programmable gain amplifier. Drive the PGA with the outut of a counter driven by a low speed clock, or the final three bits of a higher speed clock into a long counter. As those final three bits count up, the amplifier gain increases, increasing the amplitude of the sinewave output.