ejjeffrey says,"If the opamp is saturated at its negative rail and the capacitor is charged up, the device will not oscillate."

If the capacitor is at the negative rail, then the capacitor is certainly not charged up but very nearly completely discharged to a voltage very near 0-volts, but internally the Voffset of the op-amp can still bias the op-amp negative input very slightly more positive than Vin-.

ejeffrey says then, "The negative input will be at Voffset, while the positive input will be at Voffset/2"

This two inputs will actually be at the same potential(when measured externally with a DVM) but the internal voltage difference between the two inputs internally will be Voffset, not Voffset/2w.

However, the effect of the op-amp's offset voltage can be in the direction to pin the output close to the negative rail at the bottom swing of the oscillation cycle and no further oscillation occurs or it can be that the oscillator refuses to start at power up.

However, if you take a large random sample of op-amps, it is quite probable that Voffset is evenly distributed as to create in half the sample of op-amps a positive bias at Vin- and, for the remainder, a negative bias at Vin- . In other words about 1/2 of the op-amps will have an offset voltage that will will favor and permit reliable operation over some

large range of temperature operation.

When I experimentally tried a random sample of 20 LM358's in the OP's circuit, half of them worked and half of them did not.

At the same time, the input bias current of the op-amp(which is usually desired to be as low as possible as a figure of merit for an op-amp) can be used to advantage to create a reliable offset that mandates the relaxation oscillator will start and maintain oscillation over temperature if the non-inverting (+input) resistor values are chosen appropriately large so as to create a large offset favoring oscillation. In this case all of the op-amps worked reliably.

Ejeffry says, "It doesn't matter. It is an unreliable circuit."

In any circuit design, if the values of the components are chosen appropriately to best exploit the properties of the circuit components, a reliable design will result. If they are chosen without careful analysis, unexpected surprises will result.

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