What Is an SMD Inductor?

Chip inductors are also called surface-mount inductors. Like other chip components (SMC and SMD), they are a new generation of leadless or short-lead microelectronic components suitable for surface-mount technology (SMT). The welding surfaces of the lead-out ends are on the same plane.

Chip inductor

Chip inductors are also called surface-mount inductors. Like other chip components (SMC and SMD), they are a new generation of leadless or short-lead microelectronic components suitable for surface-mount technology (SMT). The welding surfaces of the lead-out ends are on the same plane.

Chinese name

Chip inductor

nickname

Surface mount inductor

Origin

Late 1970s

R & D country

Japan and the United States

Technology

SMT

Chip inductors are derived from chips with leaded multilayer ceramic capacitors used directly for placement of hybrid integrated circuits (HICs). As early as the 1960s, American JDI and Sprague companies began production. In 1977, Japan's Panasonic Corporation first adopted SMT and SMC and SMD processes in consumer electronics products such as ultra-thin semiconductor radios.

In order to meet the needs of SMT, the research and development of chip inductors began, and industrialization was soon realized.

"Chip inductors" are titles that are classified in the form of inductor structures. According to the classification of the structure and manufacturing process, inductors are divided into two types: plug-in three-dimensional inductors and chip inductors. An inductive coil (also commonly a hollow coil) is formed on the magnetic core. The characteristics of this type of inductor are large inductance range, high precision of inductance value, high power, small loss, simple manufacturing, short production cycle, and sufficient supply of raw materials. The disadvantages are low degree of automated production, high production cost, and difficulty in small size Quantification. ^[1]

Chip inductors are divided according to the manufacturing process. There are four main types of chip inductors, namely wire wound, laminated, braided and thin film chip inductors. Among them, the winding type is the product of the miniaturization of traditional winding inductors,

The difference between chip inductors and chip beads

In the topic "chip electromagnetic compatibility countermeasures device", chip inductors are mainly used to suppress the occurrence of electromagnetic interference. So comparing inductors and magnetic beads (including chip inductors and chip beads) should also start from this topic.

The inductor itself is a reactive element and it does not consume energy in the circuit. The reason why the inductor can prevent the high-frequency signal from flowing in the line and play a role in suppressing electromagnetic interference is because the inductor reflects a high-impedance element under the action of the high-frequency signal, preventing the high-frequency signal from flowing in the line. The high-frequency signal is reflected back to the interference source. As far as the frequency range of this application is concerned, few exceed 50MHz.

For the magnetic bead, it is a soft ferrite core, which is connected in series on the line that needs to suppress interference. It is true that at low frequencies, the ferrite bead still reflects as an inductor in the series circuit. However, for higher frequency interference, the reduction of the magnetic core's magnetic permeability results in a decrease in the inductance and an inductive reactance component. Therefore, the blocking effect of the magnetic bead inductance on high frequency interference is reduced. At the same time, the core loss (eddy current loss) is increasing. The latter is equivalent to a loss resistance. The increase in the resistance component causes the total impedance of the magnetic beads to continue to increase. Therefore, when high-frequency interference passes through the ferrite, the blocking effect of the magnetic beads on high-frequency interference is still increasing, but This time, instead of reflecting the high-frequency interference back to the interference source, the magnetic beads converted the high-frequency interference into the form of thermal energy and dissipated it.

From this point of view, the structure of the inductor and the magnetic beads are not fundamentally different, but from the mechanism of suppressing interference (divided according to the frequency range of suppressing interference), the two are obviously different. One is to reflect the interference back Interference source (referring to inductance), the other is to absorb the interference (referring to magnetic beads).

In electronic equipment, the electromagnetic interference we want to suppress is nothing more than the interference that occurs on signal lines and power lines. Therefore, the applicable form of inductors in electromagnetic compatibility countermeasures, especially chip inductors, is from these two aspects. analysis.

1) Filtering of signal lines

The filtering effect of signal lines is more used to deal with interference problems from space (including interference radiated from space into equipment, and interference from equipment to space). This shows that the cable is a weak link in electromagnetic compatibility, and that common mode interference is the main hazard of the device. This is the fault caused by the antenna function of the signal line. For this reason, for unshielded signal line ports, a signal line filter should be installed. The filter should be installed on the interface between the signal line in and out, and the common mode interference signals with a relatively high frequency should be filtered out.

2), the filtering of the power line

In the transmission path of equipment's electromagnetic interference, the power line is the most important medium, because the length of the power line (including the equipment's power input line and the overhead line extension of the power transmission) is sufficient to form a passive antenna for radio frequency signals. In addition, the disturbances caused by the opening, closing and operation of various equipment in the power grid also spread freely in the power grid. Such interference poses a threat to the reliable operation of sensitive equipment in the power grid. The transmission of radio frequency signals on the power line is performed in two modes. One is the common model, which appears on the two paths of the line and the ground. The other is the difference model, which propagates on the line. The power line filter is inserted in the power line and is a device specifically used to suppress the propagation of radio frequency signals. Differential mode inductors are often not used in the design of power line filters, but common mode inductors are used. The two coils of the common mode inductor are wound on the same core (the same end is on the same side of the coil). This winding method cancels out the magnetic flux generated by the differential mode current (including the power supply current), and does not generate magnetic circuit saturation. ; And the common mode current reflects a large inductance, to achieve a large filtering effect. It should be noted that the windings of the two coils of the common mode inductor cannot be completely symmetrical, so the common mode inductor actually still has a certain degree of differential mode inductance component, which still has a certain degree of suppression on differential mode interference. From this point of view, whether it is a signal line or a power line, from the perspective of suppressing electromagnetic interference, the most commonly used measure is common mode suppression. Therefore, from the point of view of using chip inductors, the most commonly used are chip common mode inductors. In addition, the inductors provided by the manufacturers of electromagnetic compatibility measures are chip common mode inductors.