voltage clamping circuit

Discussion in 'General Electronics Chat' started by ad5oj, Oct 3, 2005.

  1. ad5oj

    Thread Starter New Member

    Oct 3, 2005
    I am using an analog to digital converter to measure the output of an OP amp. The A/D converter has a maximum input voltage of 5v. However the OP amp is powered by 12v. I need to ensure that the voltage into the ADC will never exceed 5 volts without changing the linearity of any voltage below that point. If I put a reverse biased Zener diode to clamp the voltage below 5v, will it distort any signal below 5v and if so what other options are there.

    Thanks for your help,
  2. Sebi

    Well-Known Member

    Sep 24, 2005
    Use two diodes for input protection: one cathode to+5V, anode to input, the another cathode to input, anode to GND. Of course a serial resistor from opamp output needed (about 1k).
  3. beenthere

    Retired Moderator

    Apr 20, 2004

    Quick-and-dirty is to use an old CA3140 op amp. Pin 8 is a strobe, and will pull the output to 0 if it goes to 0 volts. Use a comparitor to sense 5 volts and pull the strobe pin down if that level is exceeded. - you can also use the low out of the comparitor to tell the micro that the voltage went too high.