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After understanding the principle of virtual short and virtual break,
After understanding the principle of virtual short and virtual break, we can use it to judge whether the device is good or bad in the actual application of the operational amplifier circuit. According to the principle of the virtual short of the amplifier, if the op amp works linearly, the voltages at the same input terminal and the reverse input terminal must be equal, even if there is a difference, it is at the mv level. Of course, NB-IOT wireless communication in some high input impedance circuits, the internal resistance of the multimeter will have a little influence on the voltage test, but generally it will not exceed 0.2V. If there is a difference of more than 0.5V, the amplifier must be damaged!
In many instruments and meters, there are integrated operational amplifiers for small signal amplification. It is more fragile than other integrated blocks and components, so it can be said to be a shortcut for repairing instruments and meters to quickly judge whether it is good or not. Many integrated blocks in more complicated instruments are directly welded on the printed circuit board, the circuit board is inserted into the socket, and the distance between the circuit boards is also very small, so it is difficult to directly measure the voltage. Some simple and practical methods for judging integrated op amp blocks are proposed below.
1. After powering on for a period of time, touch the temperature of the integrated op-amp block by hand. If the temperature is greater than 50°C, you should suspect whether it is damaged.
2. If possible, measure its DC current and it should be within a few milliamperes. Otherwise it is damaged.
3. The integrated op amp has a single op amp and several op amps combined, and you should be familiar with its power supply and input and output pins. There are also certain rules that can be found and found in relevant manuals. The resistance between the input pins of the integrated operational amplifier should be relatively large (generally greater than 10 M ohms). If the measured value is small, it should be observed that there is a diode with infinite value at the input end, otherwise it will be damaged.
4. The online measurement input voltage should be relatively small. Generally below 0.1 V. If you touch the input terminal with your hand, the voltage should change at the output terminal, or if you touch the two terminals of the feedback resistor with your hand (equivalent to connecting a resistor in parallel), the output will also change accordingly.
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