enter image description here

Given this circuit, I have to find \$\frac{V_2}{V_1}\$ as well as the magnitude of hysteresis.

I don't need a full solution. Any hints to approach this problem would suffice.

So far, I know the left op-amp is a Schmitt trigger and the right one has unity gain.

Edit update: Now I know that in case Schmitt trigger outputs 5V Inverting op-amp makes it -5V applying voltage divider in this case with 5 at one side and -5 at the other. I get two values either 7.5 or 2.5, 2.5 seems the correct answer but if I take 0.75R as the voltage drop for V+ then it's not correct why? Is it that the V+ automatically thinks that taking 7.5 as the reference Overshoots the saturation Voltage of the op-amp itself? update: V2/V1 graph looks like this, enter image description here

Inference: I tried to apply Voltage divider in the case where negative/positive potential was present instead of ground and I failed terribly. enter image description here enter image description here

  • \$\begingroup\$ @Joey Mallone . would you please provide me some hint regarding this problem? \$\endgroup\$ Jul 24, 2019 at 8:51
  • 1
    \$\begingroup\$ You need to show your attempt. \$\endgroup\$
    – adamaero
    Jul 24, 2019 at 15:37
  • \$\begingroup\$ Does the rule: voltages at the input terminals are equal qualify for the circuit with positive feedback or no feedback at all? \$\endgroup\$ Jul 24, 2019 at 15:51
  • \$\begingroup\$ Treat it like an ideal op-amp. Don't overthink it. \$\endgroup\$
    – adamaero
    Jul 24, 2019 at 15:54

1 Answer 1


Since the first op. amp. doesn't work in linear mode, a tip would be to start from its output in the two saturation voltages:

enter image description here

  1. Saturation voltage of the first op. amp.
  2. Output voltage of the second op. amp (gain = -1)
  3. Voltage reference for comparison (voltage divider)

The difference in the references is your hysteresis. I have no idea how can you consider a \$V_2/V_1\$ ratio if the first op. amp. is always saturated.

Simulating with a rail-to-rail op. amp.:

enter image description here


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