Inductance Basics

First, the introduction of inductance (inductance)

1. Inductance coil is a circle of wire by a circle on the insulating tube, the wires are insulated from each other, and the insulating tube can be hollow, can also contain iron or magnetic powder core, referred to as inductance. It is denoted by L.

2. Unit of inductance

   The basic unit of inductance is: H (Hen), it is the same as capacitance, is also a very large unit of measurement, we generally use uH (micro Hen), mH (milli Hen) units are used less. The relationship between them is 1000 times the calculation. 1H = 1000mH = 1000000uH

Second, the classification of inductance

1. According to the form of inductance classification: fixed inductance, variable inductance.

2. According to the nature of the magnetizing body: empty core coil, ferrite coil, iron core coil, copper core coil.

3. According to the nature of work classification: antenna coil, oscillating coil, choke coil, trap coil, deflection coil.

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

Third, the main characteristics of the inductor coil parameters

1. Inductance L    

 Inductance L represents the inherent characteristics of the coil itself, independent of the size of the current. In addition to the special inductance coil (color-coded inductance), inductance is generally not specifically marked on the coil, but with a specific name labeling.

2, inductive resistance XL  

 The size of the inductive coil to the AC current impedance is called inductive resistance XL, unit is ohm. Its relationship with inductance L and AC frequency f is XL=2πfL.

3、Quality factor Q

 Quality factor Q is a physical quantity that indicates the quality of the coil, Q is the ratio of inductive resistance XL and 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 and the DC resistance of the wire, the skeleton of the dielectric loss, shielding or core loss caused by the high-frequency skin effect and other factors. The Q value of the coil is usually tens to hundreds.

4, distributed capacitance

 Coil turns and turns, coil and shielding between the coil and the capacitance exists between the bottom plate is known as the distribution capacitance. The existence of distributed capacitance reduces the Q value of the coil, and the stability deteriorates, so the smaller the distributed capacitance of the coil, the better.

Commonly used coils

1, single layer coil

 Single layer coil is a circle of insulated wire next to a circle in the paper tube or wood skeleton. Such as transistor radio antenna coil.

2、Beehive type coil

 If the winding coil, its plane is not parallel to the rotating surface, but intersected at a certain angle, this coil is called the honeycomb coil. And its rotation week, the number of times the wire bends back and forth, often called the number of folding points. The advantages of the honeycomb winding method are small size, small distributed capacitance, and large inductance. Honeycomb winding are utilized to wind the coil, the more folding points, the smaller the distribution capacitance.

3、Ferrite Core and Iron Powder Core Coils

 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 increases the inductance and improves the quality factor of the coil.

4、Copper Core Coils

 Copper core coils are more widely used in the ultra-short wave range, utilizing the position of the rotating copper core in the coil to change the inductance, this adjustment is more convenient and durable.

5、Color coded inductors

 Color-coded inductors are inductors with a fixed inductance, and their inductance is marked by a color ring like resistors.

6、Resistance coil (choke)

 Restriction of alternating current through the coil called choke, high-frequency choke and low-frequency choke.

7、Deflection coil

 Deflection coil is the output stage of the television scanning circuit load, deflection coil requirements: high deflection sensitivity, magnetic field uniformity, high Q value, small size, low price!

V: the role of inductance and circuit applications

 1. The role of inductance and capacitance seems to be somewhat antagonistic, we have said that capacitance is a cross-blocking straight, and inductance is just the opposite, its role is to pass through the straight cross-blocking, it was well! DC through the inductor when the magnetic field generated by the size of the direction is consistent, will not change. AC power is positive and negative changes, so the magnetic field will change, as from positive (negative) to negative (positive) is a very short period of time, assuming that the first positive potential is rising, then the magnetic field around the inductor increases, to the top of the maximum, when the potential began to fall, due to the presence of a magnetic field around the inductor at this time will be converted to the magnetic field around the electrical energy so that the electrical energy can be maintained for a period of time, the reverse is the same, and thus preventing the passage of AC power. Thus, it prevents the passage of alternating current.

 2. Inductors in the circuit: inductors in the circuit of the most common function is with capacitors, composed of LC filter circuit. We already know that the capacitor has a “DC blocking, AC” ability, while the inductor has a “DC, AC blocking” function. If the accompanied by many interference signals of DC through the LC filter circuit (Figure), then, AC interference signals will be capacitors into thermal energy consumption; become more pure DC current flow through the inductor, which the AC interference signals are also turned into magnetic induction and thermal energy, higher frequency is most likely to be inductive impedance, which can inhibit higher-frequency interference signals.

3. The role of inductors in the circuit

 Basic role: filtering, oscillation, delay, trapping, etc.

 Image: “pass DC, blocking AC”.

 Refinement of the explanation: in electronic circuits, the inductor coil on the AC current-limiting effect, it and resistors or capacitors can form a high-pass or low-pass filter, phase-shifting circuits and resonance circuits, etc.; transformers can be AC coupling, voltage, current and impedance transformation.

 By the inductive resistance XL = 2πfL, the larger the inductance L, the higher the frequency f, the greater the inductive resistance. The size of the voltage at both ends of the inductor is directly proportional to the inductance L, and also directly proportional to the rate of change of current △i/△t.

 The inductor coil is also an energy storage component, which stores electrical energy in the form of magnetism, and the size of the stored electrical energy can be expressed by the following formula: WL = 1/2 Li2 . It can be seen that the greater the inductance of the coil, the greater the flow through and the more electrical energy is stored.

Symbols of inductance

Inductance Symbol: Straight, color ring, no labeling

Inductance directionality: no direction

Check inductance good or bad method: inductance meter to measure its inductance; with a multimeter to measure its on and off, the ideal inductance resistance is very small, nearly zero.

Calculation of inductance

Generally for the ring product inductance calculation, with the following way to carry out.

L (nH) = AL * N2

   Where N is the number of turns of the winding, AL core inductance coefficient, the unit is nH/N2, AL value is generally available in the core supplier catalog.

  Example: T50-52 core, inductance requirements for 330uH, calculate the number of turns required.

     From the above formula: N=(L(nH))

N=(L(nH)/AL)

      After checking, the AL value of T50-52 iron core is 33.0nH, 330uH=330000nH, substitute to get.

N=(330000/33)=100 turns

   Therefore, this inductor needs to be wound 100 turns.

Technical Terms

1 Ambient temperature

 Direct contact with the components or circuits of the temperature of the stationary air, the general method of measuring temperature

 The general method of temperature measurement is to measure the ambient temperature about 1/2 inch away from the component or circuit.

2 Color Code

 The color code of an inductor is a standardized number that corresponds to the color of the inductor.

3 Common-mode noise

  Noise or electromagnetic interference that occurs on circuits related to grounding.

4 Differential-mode noise (common-mode noise)

  Electrical interference between circuits.

5 copper loss

 The energy loss generated by current flow through a coil, which is equal to the product of the square of the current size and the coil's resistance (DCR), and which is converted to heat.

6 Iron loss (core loss)

  Iron loss is caused by the change of magnetic field in the core, this loss is related to the operating frequency and the total flow of magnetic flux.

  This loss is related to the operating frequency and the total flow of magnetic flux, the total iron loss by hysteresis loss, eddy current loss and residual loss.

7 Curie temperature

  The temperature at which the initial permeability drops to 10% of the initial permeability at room temperature is called the Curie temperature.

  Curie temperature, in the temperature above the ferrite core loss of magnetic properties, the magnetic permeability of the core

  The magnetic permeability of the iron core generally rises sharply near the Curie temperature, and at the Curie temperature, the magnetic permeability drops to about 1.0%.

  In Curie temperature, the permeability drops to about one, so that the inductance value drops rapidly.

8 Direct Current Resistance (DCR or RDC)

  The value of resistance measured at direct current.

9 Distributed Capacitance

  The amount of capacitance present between turns in an inductor coil structure.

10 Electromagnetic Interference (EMI)

  Unwanted electrical energy of any kind.

11 iron gas core (copper loss)

  A type of magnetic core that consists of crystallized iron and other elements in a gaseous composition.

  molecular structure, generally Fe2O3 and other metals, the most common combination of metal

  The most common metal combinations are manganese-zinc (Mn-Zn) and nickel-zinc (Ni-Zn).

12 Filter

  A component that filters out unwanted electrical signals.

13 Impedance

Z=(XL2+R2)½
XL=2π fL

14 Isat (Withstanding Current)

  The value of DC current that an inductor coil can withstand within the range of maximum inductance variation.

15 Temperature Rise Current (Irms)

  The value of current with which the temperature difference between the surfaces of an inductor coil can withstand under specified conditions