Electronic components often fail during use. Failure means that the circuit may malfunction, thus affecting the normal operation of the equipment. Here we analyze the failure causes and common faults of common components.
Most of the failures in electronic equipment are ultimately caused by the failure of electronic components. If you are familiar with the cause of component failure and locate the cause of component failure in time, you can eliminate the fault in time and allow the equipment to operate normally.
Temperature causes failure
One of the important factors for component failure is the effect of ambient temperature on components.
Effect of temperature changes on semiconductor devices
Since the forward voltage drop of P-N junction is greatly affected by temperature, the voltage transmission characteristics and anti-interference degree of bipolar semiconductor logic elements (TTL, HTL and other integrated circuits) composed of P-N as the basic unit are also closely related to temperature. Relationship.
When the temperature increases, the forward voltage drop of the P-N junction decreases, and its door-opening and closing levels will decrease, which makes the low-level anti-interference voltage tolerance of the component become smaller as the temperature increases; high The level anti-interference voltage tolerance increases with the increase of temperature, causing output level deviation, waveform distortion, steady-state imbalance, and even thermal breakdown.
The P-N junction, the basic unit that constitutes a bipolar semiconductor device, is very sensitive to changes in temperature. When the P-N junction is reverse biased, the reverse leakage current formed by minority carriers is affected by changes in temperature. The relationship is:
formula:
ICQ: Reverse leakage current at temperature T0C
IICQ: Reverse leakage current at temperature TR℃
T-TR: Absolute value of temperature change
It can be seen from the above formula that for every 10°C increase in temperature, ICQ will double. This will cause the operating point of the transistor amplifier to drift, the transistor current amplification coefficient to change, the characteristic curve to change, and the dynamic range to become smaller.
The relationship between temperature and allowable power consumption is as follows:
formula:
Pcm: maximum allowable power consumption
Ta: operating ambient temperature
Tj: junction temperature of the transistor