The use of magnetic ring coils is divided into three types, choke, filter, and oscillate

　　 One, choke: used in low-frequency circuits to block low-frequency AC; pulsating DC to pure DC circuits; it is commonly used in the middle of two filter capacitors at the output of a rectifier circuit. The choke and capacitor form a Π filter circuit. In the high-frequency circuit: to prevent the high-frequency current from flowing to the low-frequency end, the high-frequency choke in the old radio; get application.

Second, filtering: the same as the above theory; it also prevents the rectified pulsating DC current from flowing to the pure DC circuit. It is composed of two capacitors (electrolytic capacitors) with a choke (in order to simplify the circuit and reduce costs, use a pure resistance instead of the choke)式filter circuit. The direct current is obtained by smoothing the direct current by using the capacitor charging and discharging function and the direct current of the choke coil to block the alternating current characteristics.

　　 Three, shock: We say that rectification is to turn alternating current into direct current, so shock is the reverse process of turning direct current into alternating current. We call the circuit that completes this process an "oscillator." The waveform of the oscillator: There are sine wave, sawtooth wave, trapezoidal wave, square wave, rectangular wave, spike wave. The frequency ranges from a few HZ to dozens of GHZ. It is widely used in wired power and radio fields.

In a circuit, when current flows through a conductor, an electromagnetic field is generated. The size of the electromagnetic field divided by the size of the current is the inductance

　　The definition of inductance is L=phi/i, the unit is Weber

　　Inductance is a physical quantity that measures the ability of a coil to generate electromagnetic induction. When a current is applied to a coil, a magnetic field will be generated around the coil, and magnetic flux will pass through the coil. The greater the power supplied to the coil, the stronger the magnetic field and the greater the magnetic flux passing through the coil. Experiments have proved that the magnetic flux passing through the coil is proportional to the current flowing in, and their ratio is called the self-inductance, also called the inductance. If the magnetic flux passing through the coil is represented by φ, the current is represented by I, and the inductance is represented by L, then

L= φ/I

　　 The unit of inductance is henry (H), and millihenry (mH) or microhenry (uH) are also commonly used as the unit. 1H=1000mH, 1H=1000000uH.

　　Inductance can only work on unsteady current. Its characteristic is that the voltage at both ends is proportional to the instantaneous rate of change (derivative) of the current passing through it. The proportional coefficient is its "self-inductance"

The reason why the inductance works is that it produces a changing magnetic field when passing an unstable current, and this magnetic field will in turn affect the current. So, in this case, any conductor, as long as it passes an unstable current, will produce The changing magnetic field will in turn affect the current, so any conductor will have self-inductance.

You can see a lot of copper-wound coils on the motherboard. This coil is called an inductor. Inductance is mainly divided into two types: magnetic core inductance and air core inductance. The large inductance of magnetic core inductance is often used in filter circuits. The inductance of air core inductance is small and often used High frequency circuit.

　　The characteristics of inductance are just the opposite of those of capacitors. It has the characteristics of preventing alternating current from passing and allowing direct current to pass smoothly. The characteristic of the inductance is direct current and resistance to alternating current. The higher the frequency, the greater the coil impedance. Inductors often work with capacitors in circuits to form LC filters and LC oscillators. In addition, people also make use of the characteristics of inductance to manufacture choke coils, transformers, relays, etc.

Types of inductors

　　According to the shape, inductors can be divided into air core inductors (air core coils) and solid inductors (solid coils). According to the nature of work, inductors can be divided into high-frequency inductors (various antenna coils, oscillation coils) and low-frequency inductors (various chokes, filter coils, etc.). According to the packaging form, inductors can be divided into ordinary inductors, color ring inductors, epoxy resin inductors, magnetic ring transformers, etc. According to inductance, inductors can be divided into fixed inductors and adjustable inductors.

　　The role of inductance: pass DC, block AC

　　 Direct current: The so-called direct current means that in a direct current circuit, the inductance acts as a wire and has no effect.

　　 Resistance to AC: In an AC circuit, the inductor will have impedance, that is, XL, the current in the entire circuit will become smaller, which will hinder AC