What Is a Surface Mount Inductor?

Chip inductors, also known as power inductors, high current inductors and surface mount high power inductors. Features miniaturization, high quality, high energy storage and low resistance.

Generally, the inductors in electronic circuits are air-core coils or coils with magnetic cores, which can only withstand relatively low currents and withstand low voltages. Power inductors also have hollow coils and cores. Thick wire winding can withstand tens of amps, hundreds, thousands, or even tens of thousands of amps.

Power chip inductors are divided into two types, with and without magnetic cover, which are mainly composed of magnetic core and copper wire. It mainly plays the role of filtering and oscillation in the circuit ^[1]

There are four main types of chip inductors: wire wound, laminated, braided and thin film chip inductors. Two types are commonly used: wire wound and laminated. The former is the product of the miniaturization of traditional wound inductors; the latter is produced by multi-layer printing technology and stacking production process, and the volume is smaller than that of wound chip inductors. It is a key product developed in the field of inductor components.

Winding type

It is characterized by a wide range of inductance (mH H), high accuracy of inductance, small loss (that is, large Q), large allowable current, strong inheritance of manufacturing technology, simplicity, and low cost. There are restrictions on miniaturization. Ceramic-cored wire-wound chip inductors can maintain a stable inductance and a relatively high Q value at such a high frequency, thus occupying a place in high-frequency circuits.

TDK's NL series inductors are wire wound, 0.01 ~ 100uH, accuracy is 5%, and high Q value can meet general needs.

NLC type is suitable for power circuit, rated current can reach 300mA; NLV type has high Q value, environmental protection (recycled plastic), can be interchanged with NL; NLFC has a magnetic screen, suitable for power lines.

Laminated

It has good magnetic shielding, high sintering density, and good mechanical strength. The disadvantages are low pass rate, high cost, small inductance, and low Q value.

Compared with the wound chip inductor, it has many advantages: small size, which is conducive to the miniaturization of the circuit, the magnetic circuit is closed, and it will not interfere with the surrounding components, and it will not be interfered by nearby components, which is beneficial to the components High-density installation; integrated structure, high reliability; good heat resistance and solderability; regular shape, suitable for automated surface mounting production.

TDK's MLK type inductors are small in size, have good solderability, have magnetic screens, use high-density design, monolithic structure, and high reliability; MLG type has small inductance and uses high-frequency ceramics, suitable for high-frequency circuits; MLK operating frequency 12GHz, high Q, low inductance (1n ~ 22nH)

Thin film

It has the characteristics of maintaining high Q, high precision, high stability and small volume in the microwave frequency band. The internal electrodes are concentrated on the same level, and the magnetic field distribution is concentrated, which can ensure that the device parameters do not change much after mounting, and it has good frequency characteristics above 100MHz.

Braided

The characteristic is that the inductance per unit volume at 1MHz is larger than other chip inductors, smaller in size, and easier to install on a substrate. Miniature magnetic components for power processing.

The three most important points to consider when choosing an inductor for portable power applications are size, size, and size. The circuit board area of mobile phones is very tight and precious, especially as various functions such as MP3 players, TVs, and video are added to the phone. Increased functionality will also increase battery current consumption. As a result, modules that have previously been powered by linear regulators or connected directly to batteries require more efficient solutions. The first step to a more efficient solution is the use of a magnetic buck converter. As the name implies, an inductor is needed.

In addition to the size of the inductor, the main specifications include the inductance at the switching frequency, the DC resistance (DCR) of the coil, the rated saturation current, the rated rms current, the AC impedance (ESR), and the Q factor. Depending on the application, the choice of inductor type-shielded or unshielded-is also important.

Similar to the DC bias in the capacitor, the 2.2H inductance of manufacturer A may be completely different from that of manufacturer B. The relationship between the inductance value and the DC current in the relevant temperature range is a very important curve, which must be obtained from the manufacturer. The rated saturation current (ISAT) can be found on this curve. ISAT is generally defined as the DC current at which the inductance drop is 30 [[%]] of the rated value. Some inductor manufacturers do not specify ISAT. They may only give DC currents at temperatures above 40 ° C.

The inductive reactance XL of the chip inductor is generally not found on the parameter table of the inductive element, but it is closely related to the inductance, the classification quality factor Q of the inductive element and other parameters. It is often used in the analysis circuit. So here is a special introduction. As mentioned earlier, since the self-inductive potential of the inductor coil always prevents the current in the coil from changing, the coil has a resistance to the alternating current. The resistance is represented by the inductive reactance XL. It is not difficult to see that XL is small when the coil passes low-frequency current. XL is zero when passing direct current. Only the DC resistance of the coil acts as a resistance. Because the resistance is as small as-it is approximately short-circuited. When high-frequency current is passed, XL is large, and if L is also large, the circuit is approximately open. This characteristic of the coil is exactly the opposite of capacitance, so the use of inductive components and capacitors can form a variety of high-frequency, intermediate-frequency and low-frequency filters, as well as tuning circuits, frequency selection circuits and choke circuits.

1. When the inductor is used in wet and dry environment, high or low ambient temperature, high frequency or low frequency environment, pay attention to whether the inductor is inductive or impedance.

2.Frequency characteristics of inductor

At low frequencies, chip inductors generally exhibit inductive characteristics, which only play a role in storing energy and filtering high frequencies. However, at high frequencies, its impedance characteristics are apparent. There are phenomena such as energy consumption and fever, and reduced inductive effects. Different inductors have different high-frequency characteristics.

3, the large current that the inductor design must withstand, and the corresponding heating situation.

4. When using a magnetic ring, compare the magnetic ring part above to find the corresponding l value and the range of use of the material.

5, pay attention to the wire (enameled wire, gauze or bare wire), commonly used enameled wire. To find the most suitable thread warp ^[1] .