What are the special requirements for varistor in PCBA design?
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1. Operating temperature/storage temperature: After the varistor is mounted, the storage temperature should be kept within the operating temperature range indicated in the product specification when the circuit is not working. Do not use it in excess of the specified maximum temperature.
2. Operating voltage: Please keep the voltage applied between the terminals of the varistor below the large allowable circuit voltage. If it is used incorrectly, it will lead to product failure, short circuit and possible heat generation. When the voltage used is below the rated voltage, but it is used in the circuit where high frequency voltage or pulse voltage is continuously applied, it is necessary to fully discuss the reliability of the varistor.
3. Component heating: Please keep the surface temperature of the varistor below the maximum working temperature specified in the product specification (the temperature rise caused by component heating should be considered). The temperature rise of varistor caused by circuit conditions should be confirmed under the working condition of the actual equipment.
4. The place of use is limited. The varistor cannot be used in the following places: 1) the place with water or salt water; 2) places where dew is easy to condense; 3) Places with corrosive gases (hydrogen sulfide, sulfurous acid, ammonia, etc.); 4) The vibration or impact conditions in the place of use shall not exceed the scope specified in the product specification;
5. PCB selection: The performance of alumina PCB may be deteriorated due to thermal shock (temperature cycle).
6. Setting of pad size: The more the amount of welding, the greater the pressure on the varistor, which will lead to quality problems such as surface cracks of components. Therefore, when designing PCB pads, the appropriate shape and size should be set according to the amount of welding. When designing, please keep the pad size equal. If the amount of solder on the left and right pads is different, the solidification of the one with more solder will be delayed during soldering cooling, and cracks may appear on the other side.
7. Configuration of components: After the varistor is welded and installed on the PCB (or the PCB is bent during operation), it may cause the varistor to crack. Therefore, the bending strength of the PCB should be fully considered when configuring components, and excessive pressure should not be applied.
