IDEALPLUSING Working principle of inductor

Ⅰ. Definition of inductance:

        Inductor is a component that can convert electrical energy into magnetic energy and store it. It is a device made according to the principle of electromagnetic induction. The structure of an inductor is similar to that of a transformer, but it has only one winding.

        An inductor has a certain inductance, which only hinders the change of current. If the inductor is in a state where no current passes through it, it will try to hinder the current from flowing through it when the circuit is connected; if the inductor is in a state where current passes through it, it will try to maintain the current unchanged when the circuit is disconnected.

        Inductors are also called chokes, reactors, and dynamic reactors. In fact, any device that can produce self-inductance and mutual inductance can be called an inductor.

        Inductors are widely used. In AC circuits, inductors have the ability to hinder the passage of AC. They are often used in circuits for current blocking, voltage transformation, AC coupling, and loads; when inductors and capacitors are combined, they can be used for tuning, filtering, frequency selection, and frequency division. The simplest inductor is to wind a few turns of hollow wire, and the inductor with a magnetic core is to wind a few turns of wire on the magnetic core.

        Regardless of the type of inductor, if the structure is the same, its basic characteristics are the same, but the inductance of the inductor is different when the number of turns is different or there is a magnetic core or not. The more turns of the winding, the greater the inductance. Under the same number of turns, the inductance will increase after the coil adds a magnetic core. 

        Inductors have inductive reactance characteristics in circuits. Inductive reactance hinders the flow of current like resistance, but inductive reactance is related to the frequency of the current flowing through the inductor and the inductance of the inductor itself.

        Inductance is a path for direct current, but it has a great hindering effect on alternating current. We usually call it inductive reactance, XL=2πfL, where XL is the inductive reactance of the inductor; f is the frequency of the alternating current flowing through the inductor; L is the inductance of the inductor. Under the premise of determining the inductance, the larger the f, the greater the inductive reactance, that is, the greater the hindering effect.

Ⅱ. Working principle:

        When current passes through a wire, a concentric magnetic field will be generated with the wire as the center. At this time, if the wire is bent into a "spring shape" as shown in the figure, the magnetic flux inside the inductor will point in the same direction, thereby increasing. By adjusting the number of turns, a magnetic field proportional to the number of turns can be generated.

         This is the principle of the inductor. When current passes through an inductor, a magnetic field is generated, and conversely, a change in the magnetic field generates a current. Law of electromagnetic induction:

E = L ・(d i/d t)

L: Self-inductance of the inductor

E: Back electromotive force

 Inductance

        The back electromotive force E generated in the inductor is proportional to the rate of change of current per unit time (di/dt), so it will not occur when a constant current continuously flows in the same direction through a direct current. In other words, the inductor has no effect on direct current, but only acts as a barrier to current for alternating current. Using this property of the inductor, it can be used as a resistor (impedance) in an AC circuit.

The impedance Z (unit Ω) of the inductor is:

Z=ωL=2πfL    f is the AC frequency, and L is the self-inductance of the inductor.

Ⅲ. Symbols and units:

        Inductance symbol: L

        Inductance units: Henry (H), millihenry (mH), microhenry (uH), 1H=103mH=106uH.

        Nominal inductance: direct mark, color ring mark, no mark

        Directionality of inductance: no direction

        How to check the quality of inductance: use an inductance meter to measure its inductance; use a multimeter to measure its on and off. The ideal inductor resistance is very small, almost zero.

Ⅳ. Main technical parameters:

        ① Inductance: also known as self-inductance coefficient (L), is a physical quantity that represents the self-inductance ability of an inductor component. The units of L are H (henry), mH (millihenry) and μH (microhenry), and the conversion relationship between the three is as follows:

1H = 103mH = 106μH

        ②Quality factor: It is a parameter that indicates the quality of the inductor coil, also known as Q value or merit. The higher the Q value, the smaller the circuit loss and the higher the efficiency.

        ③Distributed capacitance: There are capacitances between the coil turns, between the coil and the ground, between the coil and the shielding box, and between the layers of the coil. These capacitances are collectively referred to as the distributed capacitance of the coil. The existence of distributed capacitance will increase the equivalent total loss resistance of the coil and reduce the quality factor Q.

        ④Rated current: It refers to the maximum working current allowed to pass through the coil for a long time.

        ⑤Stability: It mainly refers to the degree to which the parameters are affected by temperature, humidity, mechanical vibration, etc.

V. Function:

        Choke: The self-induced electromotive force in the coil always opposes the current change in the coil. It can be mainly divided into high-frequency choke coil and low-frequency choke coil.

        Tuning and frequency selection: The inductor coil and the capacitor can be connected in parallel to form an LC tuning circuit. That is, the natural oscillation frequency f0 of the circuit is equal to the frequency f of the non-AC signal, then the inductive reactance and capacitive reactance of the circuit are also equal, so the electromagnetic energy oscillates back and forth between the inductor and the capacitor, which is the resonance phenomenon of the LC circuit. During resonance, since the inductive reactance and capacitive reactance of the circuit are equal and opposite, the inductive reactance of the total current in the circuit is the smallest and the current is the largest (referring to the AC signal of f=f0), so the LC resonant circuit has the function of selecting frequency and can select an AC signal of a certain frequency f.

        Choke: It is used in low-frequency circuits to block low-frequency AC; pulsating DC to pure DC circuit; it is often used in the middle of the two filter capacitors at the output end of the rectifier circuit, and the choke and capacitor form a filter circuit. In high-frequency circuits: it prevents high-frequency current from flowing to the low-frequency end, and high-frequency chokes are used in old regenerative radios.

        Filtering: It also prevents the pulsating DC current after rectification from flowing to the pure DC circuit. The choke (in order to simplify the circuit and reduce costs, pure resistance is used instead of choke) and two capacitors (electrolytic capacitors) form a pie-type filter circuit. The capacitor charging and discharging function and the choke pass DC, and the AC characteristics are blocked to complete the smooth DC and obtain pure DC.

        Oscillation: Rectification is to convert AC into DC, and oscillation is the reverse process of converting DC into AC. Therefore, the circuit that completes this process is called an "oscillator". The waveform of the oscillator: there are sine wave, sawtooth wave, trapezoidal wave, square wave, rectangular wave, and spike wave. The frequency ranges from a few Hz to tens of GHz. It is widely used in the field of wired and radio.

VI. Detection:

        Common faults of inductors include open circuit and short circuit. In order to ensure the normal operation of the circuit, the inductor must be measured before use. The ohm range of the multimeter can be used to perform a simple measurement of the inductor, measure the DC resistance of the inductor coil, and compare it with its technical indicators: if the resistance value is much smaller than the specified resistance value, it means that the coil has a local short circuit or a serious short circuit; if the resistance value is ∞, it means that the coil has a short circuit.

VII. Precautions for use:

        ① Occasions for inductor use: Attention should be paid to humidity and dryness, high and low ambient temperature, high or low frequency environment, whether the inductor should show inductive or impedance characteristics, etc.

        ② Frequency characteristics of inductors: At low frequencies, inductors generally show inductive characteristics, that is, they only store energy and filter high frequencies. But at high frequencies, its impedance characteristics are very obvious. There are phenomena such as energy consumption and heat generation, and reduced inductive effects. High-frequency characteristics of different inductors