I. definition of inductance
Inductance: a physical quantity used to measure the electromagnetic induction capacity of a coil. When a current is fed into a coil, a magnetic field is generated around the coil, and the coil has a magnetic flux passing through it. The greater the power supply through the coil, the stronger the magnetic field and the greater the magnetic flux through the coil. It has been proved by experiments that the magnetic flux through the coil is directly proportional to the incoming current. 16. If the magnetic flux through the coil is indicated with a phi, the current with an I, and the inductance with an L, then L= phi /I. Units with Henry (H), Henry (mH), Henry (uH), 1 H = 10 ^ 3 mH = 10 ^ 6 uH.


The classification of inductance
Classification by inductance: fixed inductance, variable inductance.

Classification by magnetic properties: hollow coil, ferrite coil, iron coil, copper coil.

Classification by working property: antenna coil, oscillation coil, choke coil, trap coil, deflection coil.

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

Main characteristic parameters of inductance coil
1. Inductance L

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

2. Inductive resistance XL

The resistance of the inductance coil to ac current is called inductive XL in ohms. It is related to the inductance L and the ac frequency f as XL=2 PI fL.

3. Quality factor Q

Quality factor Q is a physical quantity representing the coil quality, Q is the ratio of inductance XL and its equivalent resistance, that is, Q=XL/R. The higher the Q value of the coil, the smaller the loss of the loop. The Q value of the coil is related to the dc resistance of the wire, the dielectric loss of the skeleton, the loss caused by the shield or core, and the effect 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 coil and shield, and between coil and plate is called distributed capacitance. The existence of distributed capacitance reduces the Q value of the coil and makes the stability worse, so the smaller the distributed capacitance of the coil, the better.

Commonly used coils

1. Single-layer coil

A single coil is a coil of insulated wire wound round and round on a paper drum or bakelite frame. Such as transistor radio medium wave antenna coil.

2. Honeycomb coil

If the winding coil is not parallel to the plane of the rotating surface, but intersecting at a certain Angle, the coil is called a honeycomb coil. And the number of times the wire bends back and forth as it rotates once is often called the number of fold points. The advantages of the honeycomb winding method are small size, small distributed capacitance and large inductance. The honeycomb coils are wound by the honeycomb winding machine. The more fold points, the smaller the distributed capacitance

3. Ferrite core and iron powder core coil

The inductance of the coil depends on the presence or absence of a magnetic core. Inserting ferrite core into the hollow coil can increase inductance and improve coil quality.

4. Copper core coil

The copper core coil is widely used in the ultra-short wave range. The position of the rotating copper core in the coil is used to change the inductance, which is convenient and durable.

5, color code inductor

The color code inductor is an inductor with fixed inductance, and the inductance marking method is the same as the resistance to mark with color ring.

6. Choke coil (choke coil)

The coil which limits the ac current passing through is called choke coil, which is divided into high frequency choke coil and low frequency choke coil.

7. Deflection coil

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