The reasons and solutions for the breakdown of the MOS tube are as follows:

, The input resistance of the MOS tube itself is very high, and the capacitance between the gate and the source is very small, so it is easily charged by the induction of external electromagnetic fields or static electricity, and a small amount of charge can form a relatively high voltage on the capacitance between the electrodes ( U=Q/C), the tube will be damaged. Although the MOS input has anti-static protection measures, it still needs to be treated with care. Pack it in metal containers or conductive materials during storage and transportation, and do not put it in chemical materials or chemical fiber fabrics that are prone to electrostatic high voltage. When assembling and debugging, tools, instruments, workbenches, etc. should be well grounded. To prevent damage caused by the operator's electrostatic interference, if it is not appropriate to wear nylon or chemical fiber clothes, hands or tools should be grounded before touching the integrated block. When straightening, bending or manually soldering device leads, the equipment used must be well grounded.

Second, the protection diode at the input end of the MOS circuit generally has a current tolerance of 1mA when it is turned on. When excessive transient input current (over 10mA) may occur, an input protection resistor should be connected in series. And 129# did not add a protection resistor in the initial design, so this is also the reason why the MOS tube may break down, and this kind of failure can be prevented by replacing a MOS tube with a protection resistor inside. In addition, because the instantaneous energy absorbed by the protection circuit is limited, too large an instantaneous signal and too high electrostatic voltage will make the protection circuit useless. Therefore, the electric soldering iron must be grounded reliably during soldering to prevent leakage of electricity from breaking down the input end of the device. In general use, the residual heat of the electric soldering iron can be used for soldering after the power is turned off, and the grounding pins of the soldering iron can be soldered first.

The basic physical characteristics of static electricity are: there is a force of attraction or repulsion; there is an electric field, and there is a potential difference with the ground; a discharge current will be generated. These three situations can have the following effects on electronic components:

1. The components absorb dust, change the impedance between the lines, and affect the function and life of the components.

2. Due to the electric field or current destroying the insulating layer and conductor of the element, the element cannot work (completely destroyed).

3. Due to the instantaneous electric field soft breakdown or overheating of the current, the component is injured, although it can still work, but its life is damaged.

In the above three cases, if the component is completely damaged, it can be detected and eliminated in the production and quality test, and the impact is less. If the component is slightly damaged, it is not easy to be found during normal testing. In this case, it is often found to be damaged after many times of processing, even when it is in use. Not only is it difficult to inspect, but also the loss is difficult to predict. The damage caused by static electricity to electronic components is no less than the loss of serious fire and explosion accidents.

Under what circumstances will electronic components and products suffer from electrostatic damage? It can be said that electronic products are threatened by electrostatic damage in the whole process from production to use. From device manufacturing to plug-in soldering, complete machine assembly, packaging and transportation, and product application, they are all under the threat of static electricity. In the entire electronic product production process, every small step in every stage, electrostatic sensitive components may be affected or damaged by static electricity, but in fact, the main and easily neglected point is the transmission and transportation of components. process.

In this process, transportation is damaged due to static electricity that is easily exposed to external electric fields (such as passing near high-voltage equipment, frequent movement of workers, rapid movement of vehicles, etc.) disputes.

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