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What's wrong with this basic configuration?

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seyyah

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Inputs to this circuit are DC and up to 10V. The output is sometimes stable and sometimes oscillates. What's the problem here? Also when the diode turns on due to high output voltage, lowering the input voltage may not help and it may oscillate or not recover from saturation. But a zener recovers in this situation. What goes on here? anybody can explain? Thanks.
 

Why not use a resistor divider on the opamp output so that the voltage can only swing 0-5V max instead of clamping the output to 5V.

If you must have it that way, then place a low value resistor of 100 Ohm in series with the opamp output inside the feedback loop.
 

E-design said:
Why not use a resistor divider on the opamp output so that the voltage can only swing 0-5V max instead of clamping the output to 5V.

If you must have it that way, then place a low value resistor of 100 Ohm in series with the opamp output inside the feedback loop.
Click to expand...

Like in the schematic? What does 100 ohm do? Does the diode have any relation with the unstability? I did not understand how to use the resistor divider when i don't know what the input voltage will be?

In the old configuration, when signal's negative (IN1-) is connected to the gnd, then the output stabilizes by the way.
 

You may be experiencing some form of latch-up. The 358 is not very prone to that, but I see you have a TLC2272 in your diagram now. The resistor helps to prevent this condition. Placing it inside the feedback loop makes the opamp to compensate for its effect on the overall output condition.
 

The LM358 is not a rail to rail opamp. With the negative power rail of the opamp connected to ground, the circuit has a hard time stabilizing when the input voltage is zero. Also, it IN- goes more positive than IN+, the circuit can never stabilize, as it cannot drive the output negative.

Try removing R11 connection to ground and connect it to a small positive voltage, like 1 to 3 volts from a battery. (By biasing the input with a dc offset, you give it some headroom and move away from the rail. ) If the oscillations go away, then you know its a headroom issue.
 

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