Detailed discussion on the method of distinguishing the positive and negative poles of SMD aluminum electrolytic capacitors

Distinguishing and measuring the positive and negative poles of the chip aluminum electrolytic capacitor. The black block with a mark on the capacitor is the negative pole. There are two semicircles on the capacitor position on the PCB. The pin corresponding to the colored semicircle is the negative pole. The length of the pin is also used to distinguish the positive and negative poles. The longer pin is positive and the shorter pin is negative.

When we don't know the positive and negative poles 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 pole of the electrolytic capacitor is connected to the positive power supply (black test pen when blocking) and the negative terminal is connected to the negative power supply (red test pen when blocking), the leakage current of the electrolytic capacitor is small (the leakage resistance is large). On the contrary, the leakage current of the electrolytic capacitor increases (the leakage resistance decreases). In this way, we first assume that a certain pole is the "+" pole, and the multimeter uses the R*100 or R*1K gear, then connect the assumed "+" pole to the black test pen of the multimeter, and the other electrode to the red test pen of the multimeter, and write down the scale where the needle stops (the needle is on the left and the resistance is large). For a digital multimeter, the reading can be read directly. Then discharge the capacitor (touch the two leads), then swap the two test pens, and measure again. In the two measurements, the one where the needle finally stopped at the left (or the resistance value was larger) meant that the black test lead was connected to the positive pole of the electrolytic capacitor.

Other:

Distinguishing positive and negative poles of chip capacitors

One is the common tantalum capacitor, which is in the shape of a rectangular parallelepiped, with the end marked with “-” as the positive end;

There is also a silver surface mount capacitor, which is probably an aluminum electrolytic capacitor. It is round on the top and square on the bottom, and is very common on optical drive circuit boards. This type of capacitor has the negative end marked with a "-".

Light-emitting diodes: The colors are red, yellow, green, and blue. The brightness is divided into three levels: normal brightness, high brightness, and super brightness. There are three commonly used packaging types: 0805, 1206, and 1210

Diode: According to the current limit, the packaging is roughly divided into two categories. The small current type (such as 1N4148) is packaged as 1206, and the large current type (such as IN4007) has no specific packaging form, only the specific size can be given: 5.5X3X0.5

Capacitors: can be divided into two categories: non-polar and polar:

The following two types of packages are the most common for non-polar capacitors, namely 0805 and 0603;

Polarized capacitors are what we usually call electrolytic capacitors. Generally, aluminum electrolytic capacitors are the most commonly used. Since the electrolyte is aluminum, its temperature stability and accuracy are not very high. SMD components are close to the circuit board, so they require high temperature stability. Therefore, most SMD capacitors are tantalum capacitors. According to their withstand voltage, SMD capacitors can be divided into four series: A, B, C, and D. The specific classification is as follows:

Type Package Type Withstand Voltage

A321610V; B352816V; C603225V; D734335V

The packaging of chip tantalum capacitors is divided into type A (3216), type B (3528), type C (6032), type D (7343), and type E (7845). The one with an angle indicates the positive pole (the one with a small triangle indicates the positive pole? I don’t know!)

Dip switches, crystal oscillators: Different specifications of SMD packages can be found in the market, and their performance and price will be related to their pin plating, nominal frequency and segment.

You can tell by the legs: the longer one is the positive pole and the shorter one is the negative pole.

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 a high temperature environment, which has a great impact on the life and stability. Solid capacitors use functional conductive polymers as dielectric materials, and will not burst when powered on if they are not used for a long time. And at low temperatures, they will not fail to achieve the desired characteristics and functions due to the slow movement of electrolyte ions. Compared with liquid electrolytes, solid capacitors have superior characteristics such as environmental protection, low impedance, high and low temperature stability, high ripple resistance and high reliability.