可恢复保险丝的内部结构

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可恢复保险丝内部结构

 

§01 解PTR


  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。

  

 

  结 ※


  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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