The traditional disposable fuse as an overcurrent protection element can only be protected once, and needs to be replaced after the fuse. Due to its self-recoverable nature, polymer self-recovery fuses can be installed and reused at a time. As a new type of over-current protection element, it has more and more applications in line protection.
1. Working principle
The polymer self-healing fuse is composed of polymer material and conductive particles. Under normal circumstances, the conductive particles form a chain-shaped conductive channel in the polymer matrix material, and the component is maintained in a low-impedance state. When an overcurrent (such as a short circuit) occurs in the circuit, the heat generated by the large current causes the polymer material to expand rapidly, cutting off the chain-shaped conductive channel, the component changes from low impedance to high impedance, blocking the circuit, protecting the load, after troubleshooting, The polymer material shrinks automatically and the conductive channels reconnect. The component itself is restored to its original state, thereby achieving the goal of "reuse without replacement, once and for all". (The working principle is shown in Figure 1,2
Second, the installation method
Since the resettable fuse has no polarity, it can be used in series with an AC or DC power supply. Shanghai WAYON's self-resetting fuses offer a variety of installation options, such as plug-in or surface mount.
3. How to choose
1 Determine the following data and requirements of the work line:
(1) Average working current (I) and working voltage (V) (no need to consider peak value)
(2) The ambient temperature (T) of the components used (the possible temperature rise should be considered)
(3) Component voltage drop / resistance requirements
(4) Action time requirements. For example, the protection time requirement of USB3.050 for USB3.0 is that the fault current is less than 8A within 5 seconds.
2 Choose product series according to V value (V≤Vmax), I value (I≤Ih) and installation method.
3 Check the corresponding table of insulation current Ih of this series of products, find the holding current value corresponding to this series of products under the ambient temperature T value, find the working current value of one or more models with Ih value greater than or equal to, that is, it is an available alternative model.
4 Test the above preliminary requirements according to the requirements of (1) and determine the best model.
4. The influence of ambient temperature on holding current and trigger current (It)
Both the holding current and the triggering current are variables related to the ambient temperature and decay as the ambient temperature increases. The attenuation is shown in Figure 3.
Fifth, the relationship between the operating time and the ambient temperature and current The speed of the self-recovery fuse changes with changes in the ambient temperature and current. Higher ambient temperature or higher current means shorter operating time.
6. Self-recovery characteristic of resistance value
After the power failure disappears, the element resistance quickly returns to the initial value. The recovery characteristics of the resettable fuse resistance over time are shown.