Recoverable fuse characteristic test

 

§01 can Restore the fuse

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One 、 Background introduction

   Last time I disassembled an electronic pet dog ,  On its internal circuit board See a relatively large recoverable fuse .  This kind of device is used in limiting circuit overcurrent protection .  Compared with other kinds of current fuses ,  It can recover by itself It brings great convenience to the application .

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Two 、 Recoverable fuse principle

   Inside the recoverable fuse , There is a special layer of matter . It contains conductive carbon particles , Embedded in organic plastic .  At normal temperature , These conductive particles are in contact with each other , The whole device is in a conductive low resistance state .  As the temperature goes up , Organic plastic expands and deforms , Destroyed the internal structure , Carbon particles do not touch each other , The device is in a high resistance state .  When the temperature drops , The organic plastic is restored to its original state , Carbon particles re contact , The device returns to a low resistance conductive state .  This is the basic principle of recoverable fuse .
  

3、 ... and 、 Characteristic analysis

   according to PTC The working principle can be known ,  Compared with ordinary fuses , Its conductivity depends on carbon particles , Therefore, the relative on resistance is relatively large .  During overcurrent protection , It does not completely block the current ,  Just limit the current to a relatively small range .  So this kind of fuse is suitable for some In electronic products with low working current .

  

Four 、 Performance measurement

   Here is the one at hand PTC Conduct characteristic measurement .   The first step is to measure its resistance ,  The second step is to measure its protection current ,  The third step is to measure its overcurrent transient characteristics ,  Finally, measure the relationship between its protection current and working voltage .

  
   Use SmartTweezer, measurement PTC The resistance of the two pins ,  The resistance value is ：  246mΩ.

  
   Using programmable power DH1766, measurement PTR Protection current ,  The output voltage is 3.3V, It can be seen that the corresponding output current is 0.488A.  You can see this recoverable insurance at hand The protection current is 0.5A, The power consumption is about 1.65W.

  
   Use Hall current sensor to detect the protection short-circuit current . The hall sensor range is set to 100mV/A.  stay PTC To impose on 3.3V, This is the current change .  from 1 Power up in seconds ;  In the following 2 The current is at 5A Saturation state . This is a DH1766 Output current limiting .  Then the current began to drop sharply .  Finally, it stabilized at 0.5A about .   so PTC The current limiting speed is relatively slow .  It takes about two seconds to limit the current to 0.5A.

  
   It's tested here PTC The dynamic characteristics of ,  It takes two seconds for the transition process to limit the current .  Finally, measure PTC The relationship between applied voltage and current .  The measurement method is relatively simple ,  utilize DH1766 Output different voltages ,  Measure the final output current limit .
  
   The output voltage is from 2V, Change to 6V,  This is the measured voltage and current curve .  You can see that as the voltage increases , The smaller the current limiting current .  Consumed in PTC The power on the remains approximately constant .  This is calculated by current and voltage PTC Power consumption on .  It can be seen that it is generally maintained at 1.5W about .

  
   about PTC The relationship between voltage and current limiting ,  Generally, there is a constant power relationship .  The higher the working voltage , The smaller the current limit is .
  
 

※ total    junction ※

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   this The characteristics of commonly used recoverable fuses are measured ,  Master its characteristics , It is very important for correct application .

  

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• Measure OUTV,OUTI
  

from headm import *
from tsmodule.tsvisa        import *
from tsmodule.tsstm32       import *

idim = []

for i in range(200):
    meter = meterval()
    printf(meter)
    idim.append(meter[0] * 10)

    time.sleep(0.1)

t = arange(200) * 0.1

plt.plot(t, idim)

plt.xlabel("Time(s)")
plt.ylabel("Current(A)")
plt.grid(True)
plt.tight_layout()
plt.show()