Operational amplifiers are very important components in analog circuits. They can form various circuits such as amplification, addition, subtraction, and conversion, and are widely used in circuit design. So, if the circuit is abnormal, how should we check whether it is the cause of the damage to the operational amplifier? M\u00f3dulo wifi inal\u00e1mbrico That is to use the "virtual short" and "virtual break" of the op amp to analyze the circuit, and then combine some small skills to judge. Next, let us first understand what is "virtual short" and "false break".Virtual shortVirtual short means that under ideal conditions, the potentials of the two input terminals are equal, so that the two input terminals can be regarded as short-circuited together, but in fact there is no short-circuit, which is called "virtual short". A necessary condition for virtual short is that the op amp introduces deep negative feedback.Due to the large voltage amplification factor of the operational amplifier, the open-loop voltage amplification factor of general-purpose operational amplifiers is above 80 dB. The output voltage of the op amp is limited, generally between 10 V and 14 V. Therefore, the differential mode input voltage of the op amp is less than 1 mV, and the two input terminals are approximately equal potential, which is equivalent to "short circuit". The greater the magnification of the open-loop voltage, the closer the potentials of the two input terminals are to the same.False breakA virtual break is when, ideally, zero current flows into the input of an integrated op amp. This is due to the infinite input resistance of an ideal op amp, as if there was an open circuit between the two inputs of the op amp. But in fact there is no open circuit, which is called "virtual break".Because the differential mode input resistance of the operational amplifier is very large, the input resistance of general-purpose operational amplifiers is more than 1M\u03a9. M\u00f3dulo ZYGBY Therefore, the current flowing into the input terminal of the op amp is often less than 1uA, which is much smaller than the current of the circuit outside the input terminal. Therefore, the two input terminals of the op amp can usually be regarded as an open circuit, and the greater the input resistance, the closer the two input terminals are to an open circuit.