Capacitance refers to the amount of charge stored under a given potential difference. It is widely used in power supply filtering, signal filtering, signal coupling, resonance, DC blocking, etc. It is an indispensable electronic component in the field of electronics and power. .
In the circuit design, there is a common understanding that "the device's margin design can be reliable if the margin is as large as possible without confidence," in fact, this view is wrong. For safety capacitors, the withstand voltage margin is too large and can cause a failure, called "low voltage failure."
The mechanism of low voltage failure is the presence of dielectric leakage current. In the case of large humidity, due to the leakiness of the capacitor, moisture can be infiltrated. When the voltage is applied to the two poles of the capacitor, the infiltrated moisture surface will form a leakage current due to its conductivity. Excessive leakage current will cause the energy storage characteristics of the capacitor. Significantly reduced, the result is the loss of the characteristics of the capacitor. This phenomenon is most likely to occur when power is applied after a humidity storage test.
Industry experts said that in order to maintain good electrical storage capacity, smooth circulation, not easily damaged by current, the choice of high-quality wire-to-board connectors is the key. When the AC power passes through the capacitor, its direction changes repeatedly, and its size also changes regularly. The capacitor is connected to the AC power supply, the capacitor is continuously charged and discharged, and the charging current and the discharging current which are consistent with the alternating current change law (phase difference) flow in the circuit. In these links, the pin header can be very good. Protective effects.
Capacitor installation considerations
a, used capacitors can no longer be used, but can be removed as a cycle check to test electrical performance;
b. If the capacitor is charged, discharge it with a resistor of about 1kΩ before use;
c. If the capacitor is stored under conditions of more than 35 ° C and humidity greater than 70%, the leakage current may rise, and the rated voltage may be applied by a resistor of about 1 kΩ before use;
d. Confirm the rated capacity, voltage and polarity of the capacitor before installation.
e. Do not use capacitors that fall on the ground;
f, the deformed capacitor should not be used;
g. The positive and negative lead spacing of the capacitor should match the position of the PCB board soldering hole. If the capacitor is forcibly inserted into a circuit board whose hole pitch is not matched, stress will act on the lead wire, which may cause the capacitor to short-circuit or increase the leakage current;
h. Insert the capacitor pins or solder pins into the PCB board during installation until the bottom of the capacitor is attached to the surface of the PCB;
i. Do not apply more than the specified mechanical pressure. When a pulling force is applied to the capacitor lead-out line, the pulling force acts on the inside of the capacitor, causing a short circuit inside the capacitor, and an open circuit or leakage current rises. The capacitor is soldered to the board and the capacitor is not shaken strongly.