Comparison of the similarities and differences between self recovery fuse and disposable fuse

Structure comparison:
A one-time fuse is generally composed of three parts:
1 the main body is a low melting point of the metal wire or metal sheet made of melt, is the fuse core.
2 electrode tip: connection circuit and melt, with good conductivity.
3 brackets: fix the melt and make the three part a rigid whole
Self recovery fuse (self recovery fuse is divided into PPTC and CPTC two kinds of polymer ceramic, the following are introduced in this paper is made of polymeric resin polymer PPTC) after special treatment (Polymer) and conductive particle distribution inside (Carbon Black). In the normal operation of polymeric resin tightly conductive particles bound in the crystalline structure, form a chain conductive pathway under the normal state of the resettable fuse resistance is too low (a few tens of milli ~ e).

Two. Comparison of self recovery fuse principle
Self recovery fuse Normal state Trip status Trip status
Fig. 1 principle of fuse action
As shown in Figure 1, for a self - restoring fuse, the heat generated by the current flowing through it is small and does not change the crystal structure. When the short circuit or circuit overload occurs when the current heat generated by the polymerization resin melt, matrix expansion, which makes the separation of soot particles, thereby forming a Trip element. When troubleshooting, re crystallization, soot particles to form conductive channel, low resistance recovery.
But for a one-time fuse, when the current overload or short circuit, the calorific value is greater than the amount of heat, the heat accumulated in the melt, once the temperature rises to the melting point of the fuse, fuse, current is cut off, after troubleshooting, not self recovery. Figure 2 self recovery fuse action curve
Specifically, the self recovery fuse action principle is a kind of energy balance, when the current flows through the self recovery fuse element, because the I2R will produce heat, and the heat generated will emit to the environment, not out will increase the temperature.
The action curve is shown in figure 2:
Point1: when the temperature is low, the heat generated all out;
Point2: when the current is too large or the environment temperature is higher, produce more heat, so as to improve the temperature of self recovery fuse, in Point 2 to achieve balance;
Point3: when the current or ambient temperature is increased, the self recovery fuse will reach a higher temperature, in Point 3 to achieve the balance (the critical point of action);
Point3 ~ Point4: at this time the current or ambient temperature continues to increase, the heat generated will be greater than the distribution, so that the temperature of the self recovery fuse components increased rapidly. In this stage, the resistance increase of temperature change will be very small. Range: self restoring fuse is in a high impedance state, limiting current to protect equipment
Three. Performance parameter comparison Table 1 Comparison of disposable fuse and self recovery fuse
Disposable self recovery fuse fuse with the main difference are shown in Table 1, most of the cases, two kinds of product performance there are still many differences, especially in the resistance / action / time / safety performance of self recovery has the obvious difference.
Application field comparison
Both can be used to make circuit over-current protection, the use of many fields and occasions are similar, there are some occasions these two products can be used, but also can replace each other. For example, in the over-current protection requirements are not too high in the application of these two types of battery protection products can lead.
However, in the protection of some important devices such as IC applications, or the power supply input / output only a one-time fuse can be competent for its protection function, these parts of the impedance requirements are also higher. In addition, in the event of a failure, it is necessary to troubleshoot troubleshooting, but also requires the use of disposable fuse.
Some must avoid overheating and burning products occasions, often need a hot plug operation interface over-current protection, simple troubleshooting, resulting in temporary and non fault circuit protection device over current select self recovery fuse.
main parameter
The main parameters are as follows:
Holding current (IH): the maximum steady state current at 25 DEG C at ambient temperature.
Action current (IT): minimum current to start protection at 25 C ambient temperature.
Maximum voltage (Vmax): the maximum voltage that can withstand under rated current.
Maximum current (Imax): the maximum current that can withstand under rated voltage.
Action time (Ttrip): the maximum operating time under the specified current.
Power loss (Pd typ): the power consumed in the operating state.
The minimum initial resistance (Rmin): normal temperature products with minimum resistance.
The maximum resistance (R1max) after the trigger: after reflow soldering or action recovery, static 1 hours after the resistance value.
Temperature derating: since a self restoring fuse is a thermal sensitive element, any ambient temperature fluctuations affect the performance of the device. As shown in figure 3:
The relationship between the current and temperature in the A zone from the time of the recovery fuse (high resistance);
B zone describes the relationship between the current and temperature of the self restoring fuse when the circuit is in normal operation;
C self recovery fuse may act or keep in a low state of resistance (depending on the components of the resistance and temperature) Fig. 3 temperature derating chart
Action time: Figure 4 shows the operating time curve of the self restoring fuse at a temperature of between 0 and 75. 75 degrees of environmental heat input is higher than 0 DEG C, so the self recovery fuse required extra power consumption (I2R) is relatively small, resulting in smaller operating current can be self recovery fuse start at a specific time (or in a given current faster action). The greater the overload current or the higher the ambient temperature, the shorter the operating time. Figure 4 action time chart