The traditional disposable fuse can only be protected once as an overcurrent protection element, and it needs to be replaced after the fuse. While the polymer self-recovery fuse can be installed and reused once. As a new type of overcurrent protection element, it is widely used in line protection.
I. Working principle of polymer self-recovery fuse
Polymer self-recovery fuse is composed of polymer materials and conductive particles. Generally, the conductive particles form chain-like conductive channels in the polymer matrix material, and the component maintains a low impedance state. When overcurrent (such as short circuit) occurs in the circuit, the heat generated by large current causes the polymer material to expand rapidly and cut off the chain-like conductive channel. The element changes from low impedance to high impedance, cutting off the circuit and protecting the load. After troubleshooting, the polymer material automatically shrinks and the conductive channels are reconnected. Its components are restored to their original state, thus achieving the purposes of reuse, no need of replacement and once and for all.
Second, the polymer self-recovery fuse selection
1. Determine the following data and requirements of the working line;
(1) average working current (I) and working voltage (v) (no need to consider peak value);
(2) Environmental temperature (t) of the used parts (possible temperature rise must be considered);
(3) Voltage drop/resistance requirements of components;
(4) Action time requirements. For example, the protection time of USB3.050 for USB3.0 requires that the fault current should be less than 8 A within 5 seconds;
2. Select product series according to V value (V≤Vmax), I value (I≤Ih) and installation method;
3. Check the insulation current Ih correspondence table of this series of products, find the holding current value corresponding to this series of products under the ambient temperature T value, and find the working current value of one or more models with Ih value greater than or equal to, that is, the usable alternative model;
4. Test the above preliminary requirements according to the requirements of (1) and determine the best model;
III. Influence of ambient temperature of polymer self-recovery fuse on holding current and trigger current (It)
Hold current and trigger current are variables related to ambient temperature, which decay with the increase of ambient temperature.
4. Relationship between Action Time and Environmental Temperature and Current The speed of polymer self-recovery fuse changes with the change of environmental temperature and current. The higher the ambient temperature or current, the shorter the running time.
V. Recovery characteristics of resistance value
After the power failure disappeared, the resistance of the components quickly recovered to the initial value. It shows the characteristic that fuse resistance can be restored at any time.
