 # The Role of Electronic Components in Circuits

What is the role of electronic components in a circuit? Let’s take a look at resistors, capacitors, diodes, triodes, etc.

1.Resistor code: R
A resistor is a component that can block the passage of current. In a circuit, it limits the amount of current flowing through the branch to which it is connected.
Functions of various electronic components in circuits
Functions: flow diversion, current limitation, voltage division, voltage reduction, isolation, offset, etc.
Judge whether it is good or bad: it is good that the actual resistance measured with the multimeter resistance block is consistent with the nominal value or within the allowable error range. (Burn out and turn black). Actual resistance measured on the road ≤ nominal value.
Resistance unit: ohm (Ω), kiloohm (K Ω), megaohm (M Ω), etc.

2.Capacitor code: C
Capacitor is a device that can hold and store electric charge, which is called capacitance for short. The circuit is generally represented by “C” plus numbers. There are two types of capacitors: non polar and polar. The long pin of the polar new capacitor is the positive pole and the short pin is the negative pole.

Characteristics: DC and AC are isolated.
Functions: isolation, coupling, bypass, filtering, tuning circuit, energy conversion control circuit, etc.
Judge whether it is good or bad: after the two poles are short circuited and discharged, use a multimeter to measure the resistance, and it is good that the needle can return to its original position after swinging out; If the needle does not return after swinging out, it is a short circuit; If the watch needle cannot return to its original position after swinging out, it is good for electric leakage; Open circuit if the needle does not swing out; Short circuit, open circuit and serious electric leakage are damage. For small capacitance, the measuring needle shall not swing, and then the series connection “electric pen method” or “AC signal method” shall be used to determine whether it is good or bad,
Capacitor structure: a component consisting of two metal films close to the lead out pin and separated by insulating dielectric materials.

Symbol:
Functions of various electronic components in circuits.Withstand voltage: refers to the highest voltage value that the capacity can accept during long-term operation, in volts (V). When replacing capacitors, the capacity shall be the same generally, and the withstand voltage shall be ≥ 1.414 times of the power supply voltage.Capacity: the size of capacity means the size of electric energy that can be stored; The blocking effect of capacitance on AC signal is called capacitive reactance, which is related to the frequency and capacitance of AC signal. Capacitive reactance XC=1/2 π fc (f represents the frequency of AC signal, C represents the capacitance).

3.Inductor code: L
Inductance coil is made by winding insulated wires on the insulating skeleton for a certain number of turns. Some of them are also added with magnetic core or iron core materials to generate inductance after being energized. It is a component that can convert electric energy into magnetic energy and store it, also known as choke, reactor and dynamic reactor. In the circuit, “L” is usually represented by a number, for example, L6 represents the inductance with the number of 6.

Symbol:
Functions of various electronic components in circuits
Inductance characteristics: DC resistance AC power. DC can pass through the coil, and the DC resistance is the resistance of the conductor itself, with very small voltage drop; When the AC signal passes through the coil, self induced electromotive force will be generated at both ends of the coil. The direction of self induced electromotive force is opposite to the direction of the applied voltage, which blocks the passing of AC. The higher the AC frequency, the greater the coil impedance.Functions: filtering, boosting, resonance, frequency division, etc. In the circuit, it can form series or parallel oscillation circuit with capacitor.

Judge whether it is good or bad: it is better if there is a certain resistance and short circuit when measuring with multimeter resistance block. (Burn out and turn black).
Inductance unit: Hen (H) Milliheng (mH) Microheng (uH)

4.Code of power transformer: B
It is formed by winding one primary coil and one or more secondary coils on the insulating framework and silicon steel sheet iron core; The principle is electromagnetic induction phenomenon, that is, the principle of electricity generating magnetism and magnetic regenerative electricity; The original coil inputs the original alternating current. The current changed by the coil generates a changed magnetic field. The changed magnetic field passes through the secondary coil, so a changed current is generated and output from the secondary coil. The transformer converts alternating current (AC).

Transformer symbol:Functions of various electronic components in circuits.The relationship between the primary secondary voltage and the number of coils is as follows:
Where N is called the voltage ratio (turns ratio). When NN2, V1>V2, the transformer is a step-down transformer, otherwise it is a step-up transformer.Functions of various electronic components in circuits.Winding formula: N1/N2=V1/V2, where V1 — input voltage V2 — and output voltage N1 — turns of primary coil ≥ 1000 and N2 — turns of secondary coil. The more turns of the transformer coil, the more obvious the electromagnetic induction is (input voltage V1=220V or 380V; secondary coil N2 determines the number of turns according to the output voltage V2). The output power is the same as the input power in the ideal transformer: P=IU (generally, the output power is only 70-90%).

5.Diode code: D or BG
It is a semiconductor component, which is formed by a PN structure. There are positive and negative poles, P is positive pole, N is negative pole; There are ordinary, voltage stabilizing, variable capacitance, light-emitting, switching, photoelectric and other diodes.Functions: rectification, voltage stabilization, capacitance variation, LED, voltage boost, switch, etc.
Good or bad judgment: use multimeter R × The positive resistance is 3-9K and the reverse resistance is ∞ (infinity) when measured by changing the probe in gear 1K.Electrode discrimination: use multimeter R × When the positive resistance is 3-9K, one end of the black probe is positive,The opposite end is negative. “Small black positive” (Note: from the appearance, the end marked with black or white is the negative pole).Diode characteristics: unidirectional conduction (current can only flow from positive pole to negative pole, while reverse direction is not conductive).

Diode symbol:Functions of various electronic components in circuits.Voltage stabilizing diode: it plays a voltage stabilizing role; The negative pole of the voltage stabilizing tube is connected to a positive voltage and the positive pole is connected to a negative voltage (contrary to the common diode connection). When the reverse voltage applied to the voltage stabilizing diode increases to a value greater than the voltage stabilizing value, the voltage stabilizing tube will be connected to form a reverse current, limiting the negative pole voltage to the voltage stabilizing value.

Light emitting diode: it is a kind of semiconductor diode, which can convert electric energy into light energy; Code LED; It also has single conductivity. The reverse breakdown voltage is about 5V. The current limiting resistor must be connected in series to control the current passing through the tube. The current limiting resistance R can be calculated by the following formula: R=(E-UF)/IF. In the formula, E is the power supply voltage, UF is the forward voltage drop of the LED, and IF is the general working current of the LED. LED uses low voltage power supply with power supply voltage between 6-24V, which reduces energy consumption by 80% compared with incandescent lamps with the same luminous efficiency; After 100000 hours of use, the light attenuation is 50% of the initial value.

Photodiode: Like ordinary diode, it is also a semiconductor device composed of a PN junction, and also has unidirectional conductivity. But in the circuit, it is not a rectification element, but a photoelectric sensor that converts optical signals into electrical signals.
Bidirectional trigger diode: a two terminal semiconductor device with symmetry. It is commonly used to trigger bidirectional silicon controlled rectifier, and is used for over-voltage protection timing, phase shifting, speed regulation, light adjustment and other purposes in the circuit. Measure the forward and reverse resistance of the bidirectional trigger diode. Under normal conditions, the forward and reverse resistance values shall be infinite. If the measured forward and reverse resistance values are very small or 0, it means that the diode has been broken down.

6.Code of unidirectional thyristor: BCR
The unidirectional silicon controlled rectifier is a semiconductor component, also known as crystal thyratron. The unidirectional silicon controlled rectifier is a four layer three terminal semiconductor device composed of three PN junction PNPNs. Compared with the diode with one PN junction, the unidirectional silicon controlled rectifier’s forward conduction is controlled by the current of the control electrode; Thyristor has no amplification effect on control electrode current.

Symbol:Functions of various electronic components in circuitsFunctions: rectification, voltage stabilization, switch, etc.Good or bad judgment: use multimeter R × The forward and reverse resistance values of AK and AG measured by changing the probe in gear 1K are ∞, the forward resistance value of GK measured by changing the probe is 3-9K, and the reverse resistance value ∞ is a good tube.Electrode discrimination: use multimeter R × Change the probe in gear 1K to measure GK. When the positive resistance is 3-9K, one end of the black probe is connected to the G (control) electrode, one end of the red probe is connected to the K (cathode) electrode, and the other end is connected to the A (anode) electrode.
working principle; The conduction conditions of silicon controlled rectifier: first, a positive voltage must be applied between the anode and cathode of silicon controlled rectifier, and second, a positive voltage must be applied to the control pole. The above two conditions must be met at the same time before the thyristor is in the conduction state. Once the thyristor is turned on, even if the control electrode voltage is reduced or removed, the thyristor is still turned on. SCR off condition: reduce or remove the forward voltage applied between the SCR anode and cathode, so that the anode current is less than the minimum sustaining current.

7.Code of bidirectional thyristor: SCR
Bidirectional silicon controlled rectifier has the characteristics of turning on and off in two directions in turn. In essence, bidirectional silicon controlled rectifier is two unidirectional silicon controlled rectifiers in reverse parallel, which is a semiconductor device formed by NPNPN five layer semiconductor with four PN structures and three electrodes. Since the structure of the main electrode is symmetrical (both are led out from the N layer), its electrode is not called anode and cathode respectively like the unidirectional silicon controlled rectifier, but called the first electrode A1 and the second electrode A2, which are very close to the control. The main disadvantage of bidirectional thyristor is its low ability to withstand voltage rise rate. This is because the carriers in each layer of the silicon chip have not returned to the cut-off position when the bidirectional silicon controlled rectifier is turned on in one direction, and corresponding protective measures must be taken.

Function: AC control circuit, such as temperature control, light control, explosion-proof AC switch, AC motor speed regulation, commutation, AC voltage stabilization and other circuits.
Electrode and quality judgment: use multimeter R × 1st gear or R × The pointer for measuring T2, T1 or T2, G pole positive and negative resistance values by changing the probe in gear 10 does not move; Use multimeter R × 1st gear or R × The positive and negative resistance values of T1 and G poles measured by changing the stylus in gear 10 are tens to hundreds of ohms. One of them must have a slightly higher resistance value, then the larger red pen is connected to G pole, the black pen is connected to T1 pole, and the rest is connected to T2 pole. Symbol:
Functions of various electronic components in circuits.

8.Triode code: BG or Q, V, T
It is a current controlled device semiconductor component, also called transistor; It is composed of two PN structures, with three electrodes, called base (B), collector (C) and emitter (E) respectively; According to the conductive type, there are PNP type and NPN type tubes; According to the power, there are three kinds of tubes: high, medium and low power tubes; There are high and low frequency tubes according to their applications; The current amplification coefficient of the crystal triode increases with the temperature. In the actual circuit, the amplification circuit and switch circuit are mainly used. It is a small current controlled large current amplification element.

Functions: amplification (voltage and current), voltage stabilization, switching, oscillation, etc.Base discrimination: use multimeter R × 1K Ω blocks one probe to fix one pole, and the other probe measures the other two poles. When the resistance values measured twice are relatively small (3-9K), the foot connected to the fixed probe is the base pole;Model discrimination: according to the color of the fixed probe when the base is measured, if the color of the fixed probe when the base is measured is red, the tube is PNP type; If the color of the fixed probe is black when measuring the base, the tube is NPN type.

Emission judgment: use multimeter R × The other two poles shall be measured by changing the stylus at 10K Ω gear, and the measured secondary resistance value shall be smaller (above 30K); The PNP tube red probe is connected to the E pole “small red hair”; The NPN type black probe is connected to the E pole “small black hair”; The other pin is C-pole.

Good or bad judgment: ① Use multimeter R × The 1K Ω gear changes the stylus to measure the B-C and B-E poles, the forward resistance is 3-9K, and the reverse resistance is ∞ (infinite); ② Use multimeter R × When the gear is 10K, change the stylus to measure the C-E pole, the forward resistance is more than 30K, and the reverse resistance is ∞ (infinite); The condition of ① ② is good.

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