可恢复保险丝内部结构
§01 拆解PTR
昨天测试了这颗来自于电子宠物狗 内部电路上的可恢复保险丝， 今天使用刻刀查看一下这个器件的内部结构。
下面是拆解这个课 PTR内部结构过程，这个过程的确比较缓慢，下面慢慢进行拆解。最后使用钳子夹扁PTR，它露出内部金属结构。 可以看到外部引线是直接焊接在外部金属壳上， 金属壳下面显露出黑色物质； 从侧面看，黑色物质是夹在上下两层金属片之间， 具有一定的厚度。 电流就是通过金属电极，黑色物质进行传递的。
下面在试图将两层金属片打开。 由于是金属壳，将其剥开还是比较困难的。 这是最后拆解的状态。
通过上述拆解剖析， 可以看到可恢复保险丝的基本结构， 就是在两个金属电极之间， 增加了正温度系数的物质。它的电阻随着温度增加呈现指数级别的增加。 当流过的电流加热PTC物质，引起温度升高，进而阻断电流进一步的增加。
※ 总 结 ※
对于电子线路中使用的可恢复保险丝，本文通过拆解查看了它的基本结构。 从另外一方面也对该期间的工作原理有了进一步的了解。 这位正确使用该器件打下了基础。
一、PTC的基本应用
如下是在 Choosing the Correct PTC Resettable Fuse 给出了使用 PTC的一些基本注意的问题：
1、确定电路参数
The PTC selected should be able to carry the inrush current along with expected overload current spikes and normal operating current. A PTC resettable fuse is a protection device only intended to operate during overcurrent and/or overtemperature events that are not normal operation and are generally undesired conditions. They are not intended to be a switch that operates numerous times in normal operation. Treating PTC fuses as switches can cause them to fatigue if cycled too many times or held in a tripped position for extended periods of time.
Also, a resettable PTC fuse is not a one-time fuse (or positive one-time disconnect). There still is a small amount of residual current that flows through the PTC when in a tripped position where a one-time fuse is a one-time disconnect that is designed to permanently open during an overcurrent event.
2、选择PTC
based on the maximum ambient temperature and steady-state current. Use thermal derating graphs/charts.
3、确定阻断时间
The time-to-trip curves are a useful tool to help determine the proper needed trip current for an application. If available, each PTC value has a colored line representing the time it takes to trip for different current values. Using the example curve in Figure 2 and following the yellow line from the top of the graph to the bottom, the PTC typically trips at the following: • 1000 seconds at 1.5 A • 1 second at 4.8 A • 0.2 seconds at 9 A • 0.03 seconds at 18 A • 0.01 seconds at 25 A
▲ 图2.1.1 阻断时间
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