Voltage Sources/ AC measurements

Discussion in 'The Projects Forum' started by dtow1, Apr 27, 2010.

  1. dtow1

    Thread Starter New Member

    Apr 27, 2010

    I am a new member here. I am working on a project to measure ac values using an ADC. I am using a voltage divider to scale down the AC line voltage into the acceptable ranges for my ADC. My ADC cannot accept negative voltages with being damaged and I am attempting to put in a dc offset.

    So far I am trying to use a summing amplifier to sum the ac signal with the dc offset.

    I am getting my DC offset from elsewhere in the circuit where there is a regulated 18Vdc. I am using a voltage divider to scale it down to 1.5 volts and a buffer/follower op amp circuit to keep it at that constant 1.5 volts, since the follower keeps the other stage from affecting this voltage.

    The problem I am running into is that the AC signal keeps going through the follower/buffer into the DC divider which is a huge issue in this circuit as the DC values supply other circuits as well.

    If anyone can point me in the right direction so that I can sum the DC and AC signals without having the AC signal traveling back into the DC voltage divider I would greatly appreciate it.

  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Why not use a precision rectifier to insure your AC becomes DC, with all peaks positive? A further suggestion is to filter the rectified AC and convert that smoothed DC, so you don't need to make a zero crossing detector to aid in synching the conversion to the waveform.
    dtow1 likes this.
  3. dtow1

    Thread Starter New Member

    Apr 27, 2010
    Hello beenthere,

    Thank you very much for your reply. I had not thought of that, If I am following you I could use the rectified AC signal, which would just be the positive peaks, which would allow me to get the peak voltage. I like that approach, thank you for the feedback, I think your suggestion will work much better than what I am trying to do, and it certainly requires far fewer components. Thanks!