SMD capacitor, also known as SMD capacitor, surface mount capacitor, the appearance is usually yellow, black or light blue. Can be divided into non-polar and polar two categories. This paper mainly discusses the polarity patch capacitor positive and negative distinction.
The positive and negative electrodes of the patch aluminum electrolytic capacitor distinguish and measure the black block marked on the capacitor as the negative electrode. There are two semicircles on the capacitor position on the PCB, and the pin corresponding to the colored semicircle is the negative pole. Also useful pin length to distinguish between positive and negative long foot is positive, short foot is negative.
When we do not know the positive and negative electrodes of the capacitor, we can use a multimeter to measure it. The medium between the two poles of the capacitor is not an absolute insulator, and its resistance is not infinite, but a finite value, generally above 1000 megohms. The resistance between the two poles of the capacitor is called insulation resistance or leakage resistance. Only when the positive terminal of the electrolytic capacitor is connected to the positive power supply (black pen when electricity is blocked) and the negative terminal is connected to the negative power supply (red pen when electricity is blocked), the leakage current of the electrolytic capacitor is small (leakage resistance is large). Conversely, the leakage current of the electrolytic capacitor increases (the leakage resistance decreases). In this way, we first assume a certain pole, the pointer multimeter selects R * 100 or R * 1K block, then connect the assumed pole with the black probe of the multimeter, and the other electrode with the red probe of the multimeter, and record the scale at which the probe stops (the resistance of the probe is large to the left),(for the digital multimeter, the reading can be directly read.) Then discharge the capacitor (touch the two leads), then switch the two pens and re-measure. In the two measurements, the black probe is connected to the positive electrode of the electrolytic capacitor when the last position of the probe is to the left (or the resistance is large).
One is a common tantalum capacitor, which is in the shape of a cuboid, and the end with the "-" mark is positive. Everyone can look at the pictures I sent;
There is also a silver surface mount capacitor, which should be aluminum electrolysis. The top is round and the bottom is square, which is very common on the optical drive circuit board. The capacitor is negative at the end marked with a.
Polar capacitors are what we usually call electrolytic capacitors. Generally, aluminum electrolytic capacitors are the most commonly used ones. Because their electrolyte is aluminum, their temperature stability and accuracy are not very high. However, chip components require high temperature stability because they are close to the circuit board. Therefore, tantalum capacitors are the most common ones. According to their different withstand voltages, patch capacitor can be divided into A, B, C, D four series, the specific classification is as follows:
Type Package Form Withstand Voltage
A, 3216,10V
B, 3528,16V
C, 6032,25V
D, 7343,35V
SMD tantalum capacitor package is divided into A type (3216),B type (3528),C type (6032),D type (7343),E type (7845). The beveled one indicates the positive pole.
Judging from the feet, the long ones are positive and the short ones are negative. On the capacitor body, the one with half color paint is the negative electrode.
(There is a special introduction in the picture I sent) The term solid electrolyte or liquid capacitor refers to the material used for its cathode. The advantage of using electrolyte as the cathode is that the capacitance can be very large. However, the electrolyte is easy to volatilize and leak in high temperature environment, which has a great influence on the life and stability. The solid capacitor uses functional conductive polymer as a dielectric material, which is not used for a long time. And at low temperatures will not be due to the slow movement of electrolyte ions and can not achieve the desired characteristics and functions, compared to liquid electrolyte, solid-state capacitors with environmental protection, low impedance, high and low temperature stability, high ripple resistance and high reliability and other superior characteristics.