Breadboard Testing

Nov 2, 2016

Tests:

• Connected AD623 to a 12V power supply for +Vs, 0V for Vs, 5V for non-inverting input, and adjusted the inverting input from 0 to 5V.
  • From this, the op-amp was deemed to be functional, as the differential was accurate, even with the non-inverting and inverting inputs at similar voltages. 
• Created circuit according to Falstad Simulation with 90k and 147k resistors for the voltage divider (R2 and R1). This allowed a maximum voltage of 4.5V with an input voltage of 12V.
  • The op amp output rapidly decreases to around 0.06V, but at a different rate compared to the voltage across the pre-charge 75 Ohm resistor.
  • Further testing is needed to ensure that the op-amp will only output close to 0V when the differential voltage across the pre-charge resistor is close to 0.
  • According to the oscilloscope reading, additional noise was added after the voltage divider, creating a sinusoidal oscillation.  

Oscilloscope Captures:

Test 1: Measured across the pre-charge 75 Ohm resistor.

• Behaves as expected, sharp spike when power is turned on, and gradually decreases to 0 in seconds.

Test 2: Measured across the two inputs going into the op-amp

• Similar to the measured graph from the pre-charge controller, but with a lower voltage as expected.  

Test 3: Measured between the op-amp's output and ground/Ref

• Time between the power on spike and reaching a value around 0 is much shorter, less than 1 second
• Appears to oscillate with increasing amplitude and decreasing value

Suggested tests for Saturday

• Recreate circuit on breadboard and on the oscilloscope, connect 1 channel across the pre-charge resistor, and another channel on the output. Determine the amount of time it takes before both reaches a value close to 0 (<0.1V)
• Try having a -Vs value of less than 0 (Use the power supplies in the electronic lab)