Op amp

意想不到1

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Where do the 13.9v and 0.04v on the right voltmeter come from? Shouldn’t they be 0?

maychang

In the first figure, the right end of R5 is suspended, and the op amp has no negative feedback. Due to the offset voltage of the op amp, the output is saturated (here it is positive saturation). In the second figure, R5 is connected to the output of the op amp, and the voltage gain of the amplifier circuit decreases (decreases to R5/R1), and the offset voltage has a small impact. The impact of the offset on the output causes a 0.04V voltage at the output. However, the second figure is still wrong. The op amp's in-phase input should be grounded through a resistor.

意想不到1

Why should the same-direction input terminal be connected to a resistor and grounded?

maychang

Unexpected 1 Posted on 2018-4-17 17:20 Why should the same-direction input terminal be connected to the ground with a resistor?

"Why should the same-direction input terminal be connected to the ground with a resistor?" In order to provide a path for the op amp input current (bias current). The current input current path is the internal resistance of the voltmeter, which is too large.

maychang

The drawing is really bad, and the most basic rules are not followed. The voltmeter in the middle blocks the value of R5, which is not allowed. In fact, you only need to move the voltmeter slightly downwards.

wsdymg

The circuit drawing is a bit perfunctory.

huo_hu

In reality, the output of Figure 1 is not certain, either saturation output or ground.