SMD patch varistor existing problems and solutions

Electronic products are widely used in daily life, but if they are used and protected improperly or used for a long time, problems will occur. If there is a problem, electronic products cannot be used. In the final analysis, there are problems with the electronic components assembled internally. Today, I will tell you how to determine whether there is a problem with the SMD patch varistorand how to solve it

First of all, let's look at the functions and uses of SMD patch varistors. SMD patch varistor is a kind of resistance device with nonlinear volt-ampere characteristics. It is very sensitive to voltage and will change with the change of voltage. It is mainly used to clamp the voltage when the circuit is under overvoltage and absorb excessive current to protect other devices

Therefore, when you find that an electronic product, such as a rice cooker and a plug-in, is no longer used, don't worry about replacing it at this time. You can disassemble it yourself to see if there is a problem with the rheostat. During the inspection process, we can use a multimeter to check whether there is a problem with the rheostat according to the resistance value of the rheostat.

During the inspection process, not only the rheostat has a problem, but also other devices have a problem. If you are not Old driver, I suggest that you send the whole electronic board to the original factory for maintenance or special maintenance points

If there is a problem with the rheostat and other equipment, and you are still an amateur electronic engineer, the problem is much simpler. You only need to replace the rheostat. There is no doubt that theSMD chip varistormust be produced by a regular manufacturer with a brand

The failure mode of the rheostat is usually short circuit. In order to prevent fire caused by short circuit of power supply due to rheostat failure, a temperature safety tube or heat release mechanism can be connected in series on each rheostat. The temperature fuse tube shall have good thermal coupling with the rheostat. When the rheostat fails (high impedance short circuit), the heat generated by it will blow the temperature fuse tube, thus separating the failed rheostat from the circuit and ensuring the safety of the equipment

When a higher power frequency temporary overvoltage acts on the rheostat, it may cause the rheostat to break down and immediately short circuit (low impedance short circuit), and the temperature fuse will blow too late, which may cause a fire

In order to avoid this phenomenon, an impact resistant power frequency fuse can be connected in series on each rheostat (in the case of aging failure, a separate power frequency fuse may not be able to fuse). The rheostat can also be used in series with the ceramic gas discharge tube. During normal operation, the ceramic gas discharge tube is not connected, and theSMD patch varistorhas no leakage current, which can greatly extend the service life; When being impacted by the surge, the ceramic gas discharge tube first breaks down, and then the surge voltage is limited by the rheostat. The total residual voltage is the sum of the two voltages, slightly increasing (tens of volts); After the impact, due to the current limitation of the rheostat, the discharge tube can not maintain continuity and extinguish the arc, and restore the normal working state; When the rheostat fails due to short circuit, the ceramic gas discharge tube will also fail rapidly due to excessive power frequency current, but most of its failure modes are open circuit, which is not easy to cause fire