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I'm trying to get a PWM modulated signal using the next circuit enter image description here
It is supposed the oscillator part changes the voltage from 2.5 V to -2.5 when reaching saturation, I was expecting something like this
enter image description here
using the variable resistor to change the duty cycle , but the output done is
enter image description here What Im missing? Its wrong done the circuit? The variable resistor is placed right?

UPDATE
After updating the circuit
enter image description here
It gets the next output enter image description here

but Im having trouble with the source since only after these values (0-25V) its behaving like the triangle source and the time on/off (duty cicle) is showing as well, I was trying to use a small source but I dint get how to correct the hysteresis; aside the oscillator part seems to be not working, even when changing the property of the variable resistor
enter image description here

I have never used a variable resistor in pspice so I don't know if this is well connected or the property well adjusted. It was expect to varyate the duty cycle by changing the value of the resistor R12.

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    \$\begingroup\$ Try removing the 330 ohm on the opamp output and better display your waveforms so at least people can know what you are probing. \$\endgroup\$
    – Andy aka
    Feb 10, 2020 at 21:17

2 Answers 2

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Voltage source V9 is dictating the across C1. Therefore, C1 is not charged or discharged through R9 and you will not see the typical RC charge and discharge curves like you drew them.
You are just probing the voltage of this voltage source.

Not familiar with the tool you use, but if possible, remove V9 and give C1 an initial voltage.

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You're driving the negative input directly from V9. As such, the negative feedback is disabled and C1 does nothing but absorb current. You probably wanted a series resistor between V9 and the negative input.

You also have far too much hysteresis. With your output around -13V, your positive input is hanging at -6.5V. Your negative input is driven by V9 and has a range of 1-5V; therefore your output will remain low indefinitely. The hysteresis should be much smaller, and instead of being centered at ground, it should be centered around 3V.

Once those are fixed, I think you'll find that introducing hysteresis works against what you're trying to accomplish by slowing down the signal. Your slow-moving output will have abrupt jumps in voltage each time the hysteresis high and low points are hit.

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