The overheat protection technology applied to an overheat protection technology in the current Intel processor may have a serious security hole. When an Intel processor-based PC is overheated or some similar situation occurs, it is vulnerable to attack. There is also an overheat protection on the circuit. In the use of varistors may be unable to control the heat, then how do we deal with these situations.
1. Hot-melt fuse technology. This technology is to install low-melting-point metal protected by wax on varistors through a certain process. When the varistor leakage current is too high and the temperature rises to a certain extent, the low-melting-point metal fuses. The varistor is removed from the circuit to effectively prevent the varistor from burning. However, thermal fuses have reliability problems, and there is only about 5 years of reliable life in a thermally-enhanced environment. In a thermally cycled environment, hot-melt fuses need to be replaced periodically to maintain normal operation.
2. Use springs to pull low melting point soldering technology. This technology is currently used by most surge arrester manufacturers' pressure limiting SPDs. A low melting point solder joint is added to the varistor pins, and then a spring is used to pull this solder joint. The varistor leakage current is too large. When the temperature rises to a certain degree, the solder of the soldering point breaks, and the welding point rapidly separates under the action of the spring tension, so that the varistor is removed from the circuit, and the alarm contact is linked and issued. Alarm signal. Because the low melting point metal will flow at the stress point and cracks will occur, the solder of the low melting point solder joint in the spring tension will also flow and crack, so the problem with this device is that the solder will age and the device will break for no reason. .
3. Temperature fuse technology. The technology connects the varistor and the thermal fuse in series and utilizes heat conduction to conduct a leakage current on the varistor. The temperature fuse blows when the temperature rises to the set temperature of the thermal fuse. Varistors are removed from the circuit. In addition to the same problems with the life and reliability of the thermal fuse, the thermal protection of the varistor with the thermal fuse has the following problems: the thermal conduction path is long, the response speed is too slow, and the heat is passed through a certain thermal conductivity medium (fill material) temperature The fuse body and the internal fuse of the thermal fuse are then passed to the temperature-safe melt, thus determining the slow response of the thermal fuse.
4. Isolation technology. This technology places the varistor in a sealed case and is isolated from other circuits to prevent varistor smog and flame from spreading. In the case of various backup protection failures, isolation technology is also a simple and effective method, but it needs to occupy a large teaching space, but also to prevent smoke and flame from taking place in the box lead hole come out.
5. Potting technology. In order to prevent the varistor from smoking when it fails, some manufacturers use this technology to potentiate the varistor. However, due to the varistor's failure, internal arcing will occur, resulting in the failure of the sealing material and the generation of carbon and carbon. The production will also maintain the arc, which will often lead to internal short circuit and black smoke, and even cause the entire equipment room to be heavily smoked. Experiments show that: after the varistor sleeve heat shrink tube, due to the heat dissipation of the varistor is affected, its dissipation power is reduced, which affects the power frequency withstand capability of the varistor. From another perspective, heat dissipation Affected will also accelerate the aging of the varistor and affect the service life of the varistor.
Keywords: varistors