Similar to how the batteries in new energy vehicles can experience thermal runaway and catch fire, the batteries in e-cigarettes also pose a risk of thermal runaway, potentially leading to explosive incidents.
To enhance the safety of e-cigarettes, in addition to ensuring battery quality and the reliability of control chips, certain countries have mandated the use of fuses and other measures for added protection. For instance, the U.S. PMTA requires products to comply with UL 8139 standard certification. Furthermore, reports indicate that some countries in the Middle East have begun to implement similar requirements.
The UL 8139 standard addresses battery protection by outlining how to implement an alternative method to safeguard the battery circuit in the event of an MCU failure, thereby providing dual circuit protection. It is understood that safety concerns arising from MCU malfunctions and thermal runaway due to lithium battery short circuits can be mitigated through the use of PTC (Positive Temperature Coefficient) protective components, ensuring enhanced safety.
PPTC（Polymeric Positive Temperature Coefficient），即高分子聚合物正系数温度元件。又称可复式保险丝（Resettable Fuse）或聚合物保险丝（Polyfuse），俗称自恢复保险丝或过流保护片（Polyswitch）。PPTC自恢复保险丝是一种理想的元件，具备过流保护功能的同时有一定的温度保护功能。
PPTC在正常工作条件下，其表现出极低的电阻值，对电路性能基本上不会产生影响。当异常电流发生或环境温度提高时，其阻值迅速提高，呈现高阻抗的状态，从而限制异常电流流过 PPTC 元件，此过程称为“动作”。当故障得到排除后，PPTC 元件自动恢复到低阻状态，此时电路又可以回到正常工作的状态。
在种类方面，自修复保险丝有插脚、低阻贴片、常规贴片、电池片等类型。
PPTC无正负极性之分。因PPTC在保护状态下，表面温度高，要安装在通风状态下，对高温敏感的元器件不要与PPTC直接接触，
PPTC自恢复保险丝，无需人工更换，经过试验连续保护1万次不失效，又称万次保险丝，可以完全取代普通热熔断体。
三、自恢复保险丝在电子烟上的应用
自恢复保险丝在电子烟中的运用主要是了提供过流保护。当电子烟产生短路或过载时，自恢复保险丝迅速增加其电阻值，从而限制通过的电流，保护电路不受伤害。
一旦故障消除，保险丝会在一段时间内冷却下来电阻值恢复到低值，允许电路重新工作。
这类自恢复功能避免了以前一次性保险丝在产生故障后更换的麻烦，提高了电子烟的安全性和用户的便利性。
一些PＴＣ保险丝还能够防油特性，这对电子烟尤其重要，由于电子烟在使用进程中会出现烟油渗漏，如果保险丝避免烟油腐蚀，将大大提高其在电子烟中的性能和可靠性。选择ＰＴＣ保险丝时，应斟酌电路的最大电流、工作温度、工作电压和直流阻抗等参数，以确保选用适合的保险丝型号。
资料来源：东莞市竞沃电子科技有限公司
原文始发于微信公众号（雾化科技展）：PPTC self-healing fuse used in electronic cigarettes
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