Why is Vcc of the op-amp -9 to +9?

Question/Problem: Why is Vcc of the op-amp -9 to +9 in the FlexiForce sample circuit?

 

Answer/Solution: The Vcc and Vee of the Op-Amp used in the FlexiForce sample circuit was chosen as +9V and -9V respectively for several reasons.

 

  1. The availability of +/-9V power supplies or batteries.
  2. The op-amp's output can swing to within 1.3V of the supply rails. This gives an output voltage of +/- 7.7V.  If the output is driven above this range, the op-amp will saturate.
  3. The circuit was set up to give a 0 to 5V output when the feedback is adjusted to match the sensor resistance at maximum pressure used.  Therefore, having a range much greater than +/- 5V is not needed.  NOTE: If a wider range is required, the op-amp power supply can be increased up to the maximum allowed on the op-amp datasheet.

Revision Date: 09/20/2007

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