Can the op amp inputs exceed the power supply range?

飞鸿浩劫

Can the op amp inputs exceed the power supply range? [Copy link]

I found the above picture when I was looking for the absolute value circuit, and then I fell into deep thought.

The op amp input can accept an input voltage beyond the power supply range after simulation. Why is this the case? Inverting amplifier circuit, power supply 5V, input -3V, but output 3V

chunyang

Generally no. The specific requirements shall be subject to the device manual and the maximum tolerance value shall not be exceeded.

飞鸿浩劫

chunyang posted on 2019-11-14 18:01 Generally no, the specific requirements shall be subject to the device manual and shall not exceed the maximum tolerance value.

But the simulation results are very puzzling. The op amp used is also a common CMOS op amp. The circuit on the first floor is a single-power supply absolute value circuit from the ADI official website. Since there is a single-power supply absolute value circuit, the input must exceed the power supply range.

maychang

In general, the op amp input cannot exceed the power supply range.

However, when simulating the circuit in the first post, the op amp inverting input does not exceed the power supply range, because when the INPUT terminal is negative, the op amp output is positive, and the op amp inverting input is zero (virtual short). If the op amp allows the input terminal to be zero, it can work normally.

飞鸿浩劫

maychang posted on 2019-11-14 18:32 Generally, the op amp input cannot exceed the power supply range. However, when simulating the circuit in the first post, the op amp inverting input did not exceed the power supply range, ...

Oh, it's short, I see.

wsmysyn

IN- is a virtual ground point, and the negative voltage is not directly applied to IO, so there is no problem. If it exceeds this level, there will be a problem, and the diode to GND will be turned on. Generally, the absolute maximum level is

GND - 0.6V, VCC + 0.6V, that is, considering the voltage drop of the diode, it is actually possible that it will be turned on at 0.4V.

飞鸿浩劫

wsmysyn posted on 2019-11-14 19:22 IN- is a virtual ground point. Negative voltage is not directly applied to IO. There is no problem. If it exceeds this level, there will be a problem. The diode to GND will be turned on. Generally, the absolute maximum level...

The diode voltage drop should not be considered

wsmysyn

Feihong Haojie published on 2019-11-14 19:39 The diode voltage drop should not be considered

The IO structure is like that. The ESD protection circuit is equivalent to a diode. It will be turned on when the range is exceeded. But there is really no need to pay too much attention to it.

chunyang

Feihong Haojie published on 2019-11-14 18:08 But the simulation results are very puzzling. The op amp used is also a common CMOS op amp. The circuit on the first floor is the single-power supply absolute value circuit on the ADI official website. ...

Because of the existence of R2, the op amp's non-inverting input is grounded. According to the virtual short principle, the level of the op amp's inverting input is 0, not a negative value. If the resistance of R2 is 0, then it is overvoltage.

飞鸿浩劫

chunyang published on 2019-11-15 13:43 Due to the existence of R2, the op amp's inverting input is grounded. According to the virtual short principle, the level of the op amp's inverting input is 0, not a negative value. If the resistance of R2 is 0, ...

Understood