Fundamentals of Electronic Components - Inductive Coils

Fundamentals of Electronic Components - Inductive Coils

An inductor coil is made up of wires wound one by one on an insulating tube, which is insulated from each other. The insulating tube can be hollow or contain an iron core or magnetic powder core, abbreviated as an inductor. Represented by L, the units include Henry (H), milliHenry (mH), and microHenry (uH), with 1H=10 ^ 3mH=10 ^ 6uH.

1、 Classification of inductors
Classified by inductance form: fixed inductance, variable inductance.
Classified by the properties of magnetic conductors: hollow core coils, ferrite coils, iron core coils, and copper core coils.
Classified by job nature: antenna coil, oscillation coil, choke coil, notch coil, deflection coil.
Classified by winding structure: single-layer coil, multi-layer coil, honeycomb coil.

2、 The main characteristic parameters of inductive coils
1. Inductance L
The inductance L represents the inherent characteristics of the coil itself, independent of the magnitude of the current. Except for specialized inductor coils (color coded inductors), the inductance amount is generally not specifically labeled on the coil, but is labeled with a specific name.
2. Antibody XL
The magnitude of the impedance effect of an inductive coil on AC current is called reactance XL, measured in ohms. Its relationship with inductance L and AC frequency f is XL=2 π fL
3. Quality factor Q
The quality factor Q is a physical quantity that represents the quality of a coil, Q is the ratio of inductive reactance XL to its equivalent resistance, i.e. 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 factors such as the DC resistance of the wire, the dielectric loss of the skeleton, the loss caused by the shielding cover or iron core, and the influence of high-frequency skin effect. The Q value of a coil is usually in the tens to hundreds.
4. Distributed capacitance
The capacitance between the turns of a coil, between the coil and the shielding cover, and between the coil and the substrate is called distributed capacitance. The presence of distributed capacitance reduces the Q value and stability of the coil, so the smaller the distributed capacitance of the coil, the better.

3、 Common coils

1. Single layer coil
A single-layer coil is made by winding insulated wires one by one on a paper tube or gluewood frame. Like a transistor radio medium wave antenna coil.
2. Honeycomb coil
If the plane of the wound coil is not parallel to the rotating surface but intersects at a certain angle, this type of coil is called a honeycomb coil. And the number of times the wire bends back and forth after one revolution is often referred to as the number of bends. The advantages of honeycomb winding method are small volume, small distributed capacitance, and large inductance. Honeycomb coils are all wound using a honeycomb winding machine, with more folding points and smaller distributed capacitance
3. Ferrite core and iron powder core coil
The inductance of a coil is related to the presence or absence of a 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
Copper core coils are widely used in the ultra short wave range. By rotating the position of the copper core in the coil to change the inductance, this adjustment is more convenient and durable.
5. Color code inductor
A color coded inductor is an inductor with a fixed inductance, and its inductance marking method is the same as that of a resistor, marked with a color ring.
6. Choke
The coil that restricts the passage of alternating current is called a choke coil, which is divided into high-frequency choke coils and low-frequency choke coils.
7. Deflection coil
The deflection coil is the load on 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.

transformer
 

A transformer is a device that converts AC voltage, current, and impedance. When there is AC current in the primary coil, AC magnetic flux is generated in the iron core (or magnetic core), causing voltage (or current) to be induced in the secondary coil. A transformer consists of an iron core (or magnetic core) and a coil, which has two or more windings. The winding connected to the power source is called the primary coil, and the remaining windings are called the secondary coils.
1、 Classification
Classified by cooling method: dry type (self cooling) transformer, oil immersed (self cooling) transformer, fluoride (evaporative cooling) transformer.
Classified by moisture-proof method: open type transformer, sealed type transformer, and sealed type transformer.
Classified by iron core or coil structure: Core type transformers (plug-in iron core C-type iron core, ferrite iron core, shell type transformer (plug-in iron core C-type iron core, ferrite iron core, ring type transformer, metal foil transformer.
Classified by the number of power phases: single-phase transformer, three-phase transformer, multiphase transformer.
Classified by purpose: power transformer, voltage regulator transformer, audio transformer, intermediate frequency transformer, high-frequency transformer, pulse transformer.
2、 Characteristic parameters of power transformer
1 Working frequency
The loss of transformer core is closely related to frequency, so it should be designed and used according to the operating frequency, which is called the operating frequency.
2 Rated power
At the specified frequency and voltage, the transformer can operate for a long time without exceeding the output power of the specified temperature rise.
3 Rated voltage
The voltage allowed to be applied on the coil of a transformer shall not exceed the specified value during operation.
4 voltage ratio
The ratio of the primary voltage to the secondary voltage of a transformer, with the difference between the no-load voltage ratio and the load voltage ratio.
5 no-load current
When the secondary of the transformer is open circuit, there is still a certain amount of current in the primary, which is called no-load current. The no-load current consists of magnetization current (generating magnetic flux) and iron loss current (caused by core loss). For a 50Hz power transformer, the no-load current is basically equal to the magnetization current.
6. No load loss: refers to the power loss measured in the primary when the secondary circuit of the transformer is open. The main loss is the iron core loss, followed by the loss (copper loss) caused by the no-load current on the copper resistance of the primary coil, which is very small.
7 Efficiency
The percentage of the ratio of secondary power P2 to primary power P1. Usually, the higher the rated power of a transformer, the higher its efficiency.
8 Insulation resistance
Indicates the insulation performance between the coils of the transformer and between the coils and the iron core. The level of insulation resistance is related to the performance, temperature, and humidity of the insulation materials used.
3、 Characteristic parameters of audio transformers and high-frequency transformers
1 Frequency response
The characteristic of the secondary output voltage of a transformer changing with the operating frequency.
2-band
If the output voltage of the transformer at the intermediate frequency is U0, the frequency range when the output voltage (input voltage remains unchanged) drops to 0.707U0 is called the passband B of the transformer.
3. Primary and secondary impedance ratio
The ratio of Ro and Ri is called the initial and secondary impedance ratio when appropriate impedance Ro and Ri are connected to the primary and secondary impedances of the transformer to match them. Under impedance matching, the transformer operates at its optimal state and has the highest transmission efficiency.