One of passive components - basic knowledge of inductance

Resistance, capacitance and inductance are common and important passive components. This series of articles will be divided into three parts to introduce the detailed basic knowledge of these three components. This paper will introduce the classification of inductors, the main characteristic parameters of inductance coils and common coils.

Part I:
One of passive components - basic knowledge of resistors (super complete)

Part II:
One of passive components - basic knowledge of capacitance (super detailed)

The inductance coil is made of wires wound on the insulating tube one by one, and the wires are insulated from each other. The insulating tube can be hollow, and can also contain iron core or magnetic particle core, which is called inductance for short. Expressed by L, the units are Henry (H), millihenry (mH), microhenry (uH), 1H=10 ^ 3mH=10 ^ 6uH.

1、 Classification of inductance

Classified by inductance form: fixed inductance and variable inductance.

Classified according to the properties of the magnetic conductor: hollow core coil, ferrite coil, iron core coil, copper core coil.

Classified by the nature of work: antenna coil, oscillation coil, choke coil, notch coil, deflection coil.

Classified by winding structure: single-layer coil, multi-layer coil, honeycomb coil.


2、 Main characteristic parameters of inductance coil

1. Inductance L
The inductance L represents the inherent characteristics of the coil and is independent of the current. Except for the special inductance coil (color coded inductance), the inductance quantity is generally not specially marked on the coil, but marked with a specific name.

2. Inductive reactance XL
The resistance of inductive coil to AC current is called inductive reactance XL, and the unit is ohm. Its relationship with inductance L and AC frequency f is XL=2 π fL

3. Quality factor Q
Quality factor Q is a physical quantity that represents the coil quality. Q is the ratio of inductive reactance XL to its equivalent resistance, that is, Q=XL/R

The higher the Q value of the coil, the smaller the loss of the circuit. The Q value of the coil is related to the DC resistance of the conductor, the dielectric loss of the skeleton, the loss caused by the shield or iron core, and the influence of high-frequency skin effect. The Q value of the coil is usually tens to hundreds.

4. Distributed capacitance
The capacitance between turns of the coil, between the coil and the shield, and between the coil and the bottom plate is called the distributed capacitance. The existence of distributed capacitance makes the Q value of the coil decrease and the stability become worse, so the smaller the distributed capacitance of the coil, the better.

3、 Common coil

1. Single-layer coil
Single-layer coil is wrapped on the paper tube or bakelite frame with insulated wires one by one. Such as transistor radio medium wave antenna coil.

2. Honeycomb coil
If the plane of the winding coil is not parallel to the rotating surface, but intersects at a certain angle, this coil is called honeycomb coil. The number of times the wire bends back and forth when it rotates for one cycle is often called the number of bends. The honeycomb winding method has the advantages of small volume, small distributed capacitance and large inductance. The honeycomb coil is wound by the honeycomb winding machine. The more the fold points, the smaller the distributed capacitance

3. Ferrite core and iron powder core coil
The inductance of the coil is related to the presence or absence of magnetic core. Inserting a ferrite core into an empty core coil can increase the inductance and improve the quality factor of the coil.

4. Copper core coil
The copper core coil is widely used in the ultra-short wave range. The position of the copper core in the coil is rotated to change the inductance. This adjustment is more convenient and durable.

5. Color code inductor
Color code inductor is an inductor with fixed inductance, and its inductance marking method is the same as that of resistance, which is marked by color ring.

6. Choke
The coil that limits the passage of alternating current is called choke coil, which is divided into high-frequency choke coil and low-frequency choke coil.

7. Deflection coil
The deflection coil is the load of the output stage of the TV scanning circuit. The deflection coil requires high deflection sensitivity, uniform magnetic field, high Q value, small size and low price.