Design Requirements of Varistor in PCBA Design
Special requirements for varistors in PCBA design. This circuit board manufacturer is a professional PCBA chip processor with rich production and processing experience. What are the requirements for varistors in PCBA design?
1. Operating temperature/storage temperature:
Keep the operating temperature of the circuit within the operating temperature range specified in the product specification. After mounting, the storage temperature when the circuit is not working shall be kept within the service temperature range specified in the product specification. Do not use at a high temperature that exceeds the specified maximum operating temperature.
2. Applied voltage
The voltage applied between the varistor terminals shall be kept below the maximum allowable circuit voltage. If it is used incorrectly, it will lead to product failure, short circuit, and may generate heat. The voltage used is below the rated voltage, but when it is used in the circuit where high frequency voltage or pulse voltage is continuously applied, the reliability of the varistor must be fully discussed.
3. Element heating
The surface temperature of the varistor shall be kept below the maximum working temperature specified in the product specification (the temperature rise caused by the heating of the element itself shall be considered). The temperature rise of the varistor caused by the circuit conditions shall be confirmed under the actual working condition of the equipment.
4. The use place is limited. The varistor cannot be used in the following places:
1) Places with water or salt water;
2) Places prone to condensation;
3) Places with corrosive gases (hydrogen sulfide, sulfurous acid, * *, ammonia, etc.);
4) The vibration or impact conditions at the place of use shall not exceed the scope specified in the product specification;
5. Circuit board selection
The serviceability of alumina circuit boards may be degraded by thermal shock (temperature cycling). When using, it is necessary to confirm whether the circuit board has an impact on the product quantity.
6. Setting of pad size
The more welding, the greater the pressure on the varistor will be, and it will cause quality problems such as component surface cracks. Therefore, when designing the PCB pad, the appropriate shape and size must be set according to the welding amount.
When designing, please keep the size of pads equal to the left and right. If the solder amount of the left and right pads is different, the solidification of the side with more solder amount will be delayed during welding cooling, and the other side may be subject to stress resulting in cracks in the components.
7. Configuration of components
The project after the varistor is welded and installed on the circuit board, or if the circuit board is bent during operation, the varistor may break. Therefore, the bending strength of the circuit board shall be fully considered when configuring components, and excessive pressure shall not be applied.
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