Author - fee is proud Source - Flyboat Electronics Co., Ltd. of Guizhou

1. Foreword 

Pressure limiting type SPD basically use the tiles ZnO varistor (MOV), and the use of MOV geometry is usually large, large flow passage. Deterioration of ZnO Varistor failure manifested as movements continue to lower voltage, leakage current is increasing steadily, is a short circuit mode, when the leakage current continues to grow to a few mA ~ a few amperes, the temperature will continue to rise, if the can not cut off the circuit, will cause the breakdown led to MOV chip is hot-melt, once the chip is hot-melt MOV breakdown, it becomes a low resistance conductor, causing the system short-circuit and significantly reduce heat, heat from the protection agencies will lose effect. Will cause a serious fire, damage to equipment, serious consequences. Therefore, on the use of ZnO film pressure limiting valve type SPD, the failure to protect its core technology.  Can effective fail-safe, to prevent the accident, is related to the rise and fall of the whole industry a big problem. 

Heat from the MOV protection agencies must be achieved before the chip is hot-melt from the breakdown, in which there are two directions for improvement: a. heat from the protection of institutional structures to improve, so that low melting point alloy solder melting point of the time required for the shortest; b. MOV to extend as much as possible before the chips are hot melt adhered to the breakdown of time to ensure that heat from the body of the low melting point alloy solder melting; large heat capacity MOV chip is designed for this purpose.

2. To protect the structure from the existing thermal problems: 

2.1 out of traditional SPD thermal protection principle is the use of MOV chip failure after the load of the role of frequency, its leakage current growing cause chip heating the heat from the body of the low melting point alloy solder melting point, using the spring tension of the loop from the weld pull away from cut off the circuit to achieve the protective purpose. For example, many foreign companies in almost all lightning protection modules and domestic manufacturers such as the module's internal structure are so complicated structure of its Molded, mold expensive.

2.2 The structure because of spring tension, there will be two kinds of cases does not work: 

a. heat from the body of the deformed stuck, plastic case thermal deformation, spring break the plastic support column protection agencies such as lead failure, can not be separated, resulting in a fire-induced fires; b. chip has not yet expired, the welding point of the spring tension due to the long creep under the action of which was torn off and replaced frequently due to malfunction caused by the loss, which if it occurred in the mountains unattended, particularly when the base station not be tolerated. 

3. The new SPD for the basic principle and structure:

3.1 Basic principle:

The patent's basic electrical schematic diagram, and one of the most simple external circuit schematic diagram instructions see the figure below. External direct line can be used in the module can also be needed on the outside (the module size can be smaller). 

External direct line to the principle of description: As the light-emitting diode (LD) only 2 ~ 3mA of current can be lit, they can be a large resistor in series resistance, so that, when subjected to lightning, over voltage surge mainly by the resistance commitment will not be diode Jihuai.

3.2 works as follows: 

Through the internal structure improvements, the use of pressure-sensitive chip deterioration caused by a post-heating temperature of the chip, would constitute a loop of metal fuse (optional low melting point metal) fuse in order to achieve the purpose of open-circuit protection, fuse on the chip close to the surface the shortest distance from the thermal conductivity, thermal fusing time required for the shortest, and thus greatly increased reliability, since there is no mechanical tension, will not be broken down not open or wrong situation.

3.3 patent design plastic case of simple structure, can be done according to the volume needs to be small, such as using a standard 34 × 34 chip module size of 45 × 45 × 18 (with fault instructions), using the patent can be size reduced to 38 × 40 × 18 (with a fault indication lines). 

All in all, this patent has the following characteristics:

1. The use of the inherent properties of materials, Chase flow, high reliability and thermal fuse protection agencies; (large area direct heat transfer method) 

2. No mechanical spring tension structure, Molded Case structure is simple;

3. All electronic instructions and signal output. 

The following is an example of product, a red soft wire for external direction or signal output.  Can be used for the following occasions: 

1. Complete set of equipment can be integrated in an important, highly reliable power supply in order to provide the most secure internal lightning surge protection;

2. For lightning protection box to replace the plug-in module in order to reduce costs;

3. Other appearance less demanding occasions.