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I got a feed forward controller differential op-amp here. so its v+=v-.
how ever once i increase R9 to more then 6k, v- starts changing rapidly in respect to v+, as can be seen by the images, any one know why that is happening?
I got a feed forward controller differential op-amp here. so its v+=v-.
how ever once i increase R9 to more then 6k, v- starts changing rapidly in respect to v+, as can be seen by the images, any one know why that is happening?
In both cases, your output is railed to the supply. In this region, the way the opamp changes its outputs is not very well defined. In addition to this, the model used for PSPICE likely doesnt model this region of operation very well.
Your problem is your circuit. Work out the math first. For proper circuit operation, you need to keep the opamp linear. Ways to fix your issue are reducing the 5V offest input, or reduce your 6k/7k to something that keeps the opamp within its power supply output range (check datasheet) - probably something like +/-1.5V from the supply rails.
How about an explanation of what you need the amplifier to do?
PSPICE is not going crazy - it's telling you something about your design.
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