[electronic device note 4] inductance parameters and type selection

introduction

I plan to learn electronics again recently , Take notes , There's this series , Notes are from B standing up Master Tang spoke about the excerpt from the video game , Share and learn with you . I hope I can make progress step by step .

Take a wire and wind it around the pen , Take it down to a hollow inductor , If you take an iron core , Wrap the same number of turns around the iron core , The inductance of the added iron core is thousands or even tens of thousands of times that of the non added iron core , Therefore, the inductance is generally with iron core . The following is the model of inductance ：

1. Classification of inductors

According to the package, inductors can be divided into in-line （ Specifically, the color separation ring inductance 、 Color coded inductance 、 I-inductance 、 Plastic encapsulated I-shaped inductor 、 Hollow inductance coil 、 Magnetic loop inductance 【 Huang Baihuan 、 Iron silicon aluminum 】、 Magnet winding inductance 、 Common mode choke 、 A magnetic ring 、 Magnetic beads 、 High frequency transformer ） And patches （ Specifically, it is also divided into chip inductors and wire art chip inductors ） Two kinds of .

According to whether there is shielding or not, it is also divided into shielded inductance and unshielded inductance .

When current flows through a wire , The magnetic field is established in the magnetic core , In practice, the current flowing through the inductor changes rapidly , So the magnetic field is also changing rapidly , If it is not shielded, it will cause the problem of electrofusion interference . To shield the magnetic field, the inductor is generally enclosed by magnetic conducting materials , Inductive N Extreme harmony S Poles produce tight coupling , The magnetic field forms a circuit in this magnetic conducting material , In this way, the magnetic field is shielded .

2. Parameters of inductance

The important parameters of inductance mainly include ： precision 、 Flow capacity （lrms)、 DC resistance (DCR)、 Self resonant frequency (SRF)、 Saturation current (Isat).

2.1 precision

Expressed as a percentage , such as 1.0±30%μH, Accuracy of ±30%.

2.2 DC resistance (DCR)

DC resistance (DCR): DC resistance value of inductance , It depends on the number of coils wound and the diameter of the wire . Generally, the thicker the wire around the inductance DCR The smaller it is , In order to improve efficiency, switching power supply can adopt DCR Relatively small inductance .

2.3 Flow capacity (Ims)

The inductance will heat up due to resistance loss , Under the condition that the heat does not damage the inductance , Maximum allowable continuous current .

2.4 Self resonant frequency (SRF)

Due to parasitic capacitance in inductance , The inductance and its parasitic capacitance have resonance frequency , At this frequency, the maximum inductance impedance exceeds the resonance frequency, and the impedance begins to drop , Present compatibility .

2.5 Saturation current (Isat)

Inductance with magnetic core , When the current increases to a certain extent , The magnetic field strength no longer increases , If the current continues to increase, the inductance of the component will decrease rapidly . This current is called saturation current , So if the inductor with magnetic core works normally , Do not make the peak current exceed the saturation current . There is no saturation current in hollow inductors without magnetic cores , Its magnetic field increases with the increase of current , The inductance does not change .

• The three most important indicators of inductance are DC resistance (DCR)、 Flow capacity (Ims) and Saturation current (Isat).
• If the data book gives the saturation current (Isat) Value , Usually take Isat Of 80% Is the maximum current that can flow （ There is a margin ）.

3. The inductance value indicates

3.1 Chip inductors

The number on the chip inductor is generally 3 position , The last one is 10 The power of , The number before the last digit is the multiplier , Unit is μH, for example ：

151：$15\times 10^1=150\mu H$

If the inductance says R, Just put R When the decimal point , for example ：

4R7：$4.7\mu H$

127 Commonly used ：12mm12mm7mm The most commonly used .

3.2 Wire art chip inductor

The number on the wire art chip inductor is generally 3 position , The last one is 10 The power of , The number before the last digit is the multiplier , Unit is nH, for example ：

152：$15\times 10^{2}nH=1.5\mu H$

Reference material
[1] Mr. Tang talked about electronic competitions. Mr. Tang talked about electronic devices （1） Inductance parameters and selection