Electronic components are the knowledge that electronic engineers must master. Today, Xiaobian came to a big summary. The article is a bit long, but it is all dry goods. Collect it~
1. Resistance
The resistor is represented by "R" plus a number in the circuit, such as: R15 represents the resistor numbered 15. resistance in a circuit
The main functions are shunt, current limit, voltage divider, bias, filter (combined with capacitor) and impedance matching.
1. Parameter identification: The unit of resistance is ohm (Ω), and the unit of magnification is: kilo-ohm (KΩ), megohm (MΩ), etc. The conversion method is:
1 megohm = 1000 dry ohms = 000000 ohms, there are 3 ways to label the parameters of the resistance, namely the direct labeling method, the color labeling method and the numerical labeling method.
The numbering method is mainly used for small-volume circuits such as patches, such as:
472 means 47X100Ω (ie 4.7K); 104 means 100KΩ
The color circle labeling method is most used, and the examples are as follows:
Four-color ring resistance - five-color ring resistance (precision resistance)
The relationship between the color code position and magnification of the resistor is shown in the following table:
Color, significant figures, magnification, tolerance (%)
Silver / 10-2±10
Gold / 10-1±5
Black 0 100/
Brown 1 101±1
Red 2 102±2
Orange 3 103/
Yellow 4 104/
Green 5 05±0.5
Blue 6 106±0.2
Purple 7 107±0.1
Grey 8 108/
White 9 109+5 to -20
Colorless // ±20
2. Capacitance
1. Capacitors are generally represented by "C" plus numbers in the circuit (for example, C25 represents the capacitor numbered 25). A capacitor is a component composed of two metal films that are close together and separated by insulating materials. The characteristics of capacitors are mainly to block DC and AC.
The size of the capacitance is the amount of energy that can be stored. The blocking effect of the capacitor on the AC signal is called capacitive reactance, which is related to the frequency of the AC signal and the capacitance. Capacitive reactance XC=1/2Ï€fc (f represents the frequency of the AC signal, C represents the capacitance)
The types of capacitors commonly used in telephones include electrolytic capacitors, ceramic capacitors, chip capacitors, monolithic capacitors, tantalum capacitors and polyester capacitors.
2. Identification method: The identification method of capacitance is basically the same as that of resistance, and it is divided into three types: direct marking method, color marking method and number marking method. The basic unit of capacitance is expressed in farad (F), and other units are: millifarad (mF), microfarad (uF), nanofarad
(nF), picofarads (pF).
Where: 1 farad = 103 millifarads = 106 microfarads = 109 nanofarads = 1012 picofarads. The capacitance value of a capacitor with a large capacity is directly marked on the capacitor. For example, a capacitor with a small capacity of 10uF/16V has a capacity value represented by letters or numbers on the capacitor.
Letter notation: 1mF1000uF...1P2=1.2PF1n=1000PF
Digital representation: Generally, three digits are used to represent the capacity, the first two digits represent significant digits, and the third digit is the magnification.
For example: 102 means 10X102PF=1000PF 224 means 22X104PF=0.22uF
3. Capacitance error table
For example: a ceramic capacitor of 104J means that the capacitance is 0.1uF, and the error is ±5%.
4. Fault characteristics
In actual maintenance, the failures of capacitors are mainly manifested as:
(1) Open circuit failure caused by pin corrosion.
(2) Open circuit failure of desoldering and virtual soldering.
(3) Small volume or open circuit failure caused by liquid leakage.
(4) Leakage, serious leakage and breakdown faults.
3. Crystal diode
Crystal diodes are often represented by "D" plus numbers in circuits
Such as: D5 represents the diode numbered 5.
1. Function: The main characteristic of the diode is unidirectional conductivity, that is, under the action of forward voltage, the on-resistance is very small; while under the action of reverse voltage, the on-resistance is extremely large or infinite. Because the diode has the above characteristics, it is often used in rectification, isolation, voltage regulation, polarity protection, coding control, FM modulation and squelch circuits in cordless telephones.
The crystal diodes used in telephones can be divided into: rectifier diodes (such as 1N4004), isolation diodes (1N4148), Schottky diodes (such as BAT85), light-emitting diodes, and Zener diodes.
2. Identification method: The identification of diodes is very simple. The N pole (negative pole) of low-power diodes is mostly marked with a color circle on the surface of the diode. Some diodes also use diode-specific symbols to indicate P pole (positive pole) or N pole. (Negative), there are also symbols marked "P" and "N" to determine the diode polarity. The positive and negative poles of the light-emitting diode can be identified from the length of the pins. The long pin is positive and the short pin is negative.
3. Test precautions: When using a digital multimeter to test the diode, the red test lead is connected to the positive electrode of the diode, and the black test lead is connected to the negative electrode of the diode. The resistance value measured at this time is the forward conduction resistance value of the diode. The connection method of the multimeter's test leads is just the opposite.
4. The withstand voltage comparison of commonly used 1N4000 series diodes is as follows:
Models 1N4001, 1N4002, 1N4003, 1N4004, 1N4005, 1N4006, 1N4007
Withstand voltage (V) 50, 100, 200, 400, 600, 800, 1000
Current (A) is 1
4. Zener diode
Zener diodes are often represented by "ZD" plus numbers in circuits
Such as: ZD5 represents the voltage regulator tube numbered 5.
1. The voltage regulation principle of the Zener diode: The characteristic of the Zener diode is that after breakdown, the voltage across it remains basically unchanged. In this way, when the voltage regulator tube is connected to the circuit, if the voltage of each point in the circuit fluctuates due to fluctuations in the power supply voltage or other reasons, the voltage across the load will remain basically unchanged.
2. Fault characteristics: The fault of the Zener diode is mainly manifested in open circuit, short circuit and unstable voltage regulation value. Among these 3 kinds of faults, the former fault shows that the power supply voltage rises; the latter two faults show that the power supply voltage drops to zero volts or the output is unstable.
The types and voltage regulator values ​​of commonly used Zener diodes are as follows:
5. Inductance
Inductance is commonly used in circuits to "process digital representation"
Such as: L6 represents the inductor numbered 6.
The inductance coil is made by winding an insulated wire on an insulated skeleton for a certain number of turns.
DC can pass through the coil, the DC resistance is the resistance of the wire itself, and the voltage drop is very small; when the AC signal passes through the coil, a self-induced electromotive force will be generated at both ends of the coil, and the direction of the self-induced electromotive force is opposite to the direction of the applied voltage, hindering the AC voltage. Pass through, so the characteristic of the inductor is to pass DC and resist AC. The higher the frequency, the greater the coil impedance. The inductance can form an oscillation circuit with the capacitor in the circuit.
Inductors generally have direct marking method and color marking method, and the color marking method is similar to resistance.
Such as: brown, black, gold, gold means 1uH (error 5%) inductance.
The basic unit of inductance is: Henry (H) conversion unit: 1H=103mH=106uH.
6. Varactor diode
The varactor diode is a special diode specially designed according to the principle that the junction capacitance of the "FN junction" inside the ordinary diode can change with the change of the applied reverse voltage. The varactor diode is mainly used in the high-frequency modulation circuit of the mobile phone or the landline in the cordless telephone to realize the modulation of the low-frequency signal to the high-frequency signal and transmit it. In the working state, the modulation voltage of the varactor diode is generally added to the negative electrode, so that the internal junction capacitance of the varactor diode changes with the change of the modulation voltage.
The failure of the varactor diode is mainly manifested as leakage or poor performance:
(1) When the leakage phenomenon occurs, the high-frequency modulation circuit will not work or the modulation performance will be deteriorated.
(2) When the variable capacitance performance becomes poor, the operation of the high-frequency modulation circuit is unstable, so that the modulated high-frequency signal is sent to the other party and received by the other party and distorted. When the above situation occurs, the varactor diode of the same type should be replaced.
7. Transistor
Transistors are often represented by "Q" plus numbers in circuits, such as: Q17 represents the transistor numbered 17.
1. Features: The crystal triode (referred to as triode) is a special device with 2 PN junctions inside and with amplifying ability. It is divided into two types: NPN type and PNP type. These two types of transistors can complement each other in terms of working characteristics. The so-called pair tube in the OIL circuit is paired with the FNP type and the NPN type.
FNP-type transistors commonly used in telephones are: A92, 9015 and other models; NFN-type transistors are: A42, 9014, 9018, 9013, 9012 and other models.
2. The transistor is mainly used for amplification in the amplification circuit, and there are three connection methods in common circuits. In order to facilitate comparison, the characteristics of the three connection circuits of transistors are listed in the following table for your reference.
Continuation table
Application of multi-stage amplifier intermediate stage, low frequency amplification input stage, output stage or high frequency or broadband circuit and constant current source circuit for impedance matching
3. Online work test
In the actual maintenance, the triodes have been installed on the circuit board. It is really a hassle to remove each one for testing, and it is easy to damage the circuit board. For your reference:
Eight, field effect transistor amplifier
1. Field effect transistors have the advantages of high input impedance and low noise, so they are also widely used in various electronic devices. In particular, the input stage of the entire electronic device can obtain performance that is difficult to achieve by ordinary transistors by using field effect transistors.
2. Field effect transistors are divided into two categories: junction type and insulated gate type, and their control principles are the same. As shown in Figure 1-1-1, there are two types of symbols:
3. Comparison of FET and transistor
(1) Field effect transistors are voltage-controlled elements, while transistors are current-controlled elements. In the case that only less current is allowed to be taken from the signal source, the field effect transistor should be selected; and when the signal voltage is low and more current is allowed to be taken from the signal source, the transistor should be selected.
(2) Field effect transistors use majority carriers for conduction, so they are called unipolar devices, while transistors have both majority carriers and minority carriers for conduction. are called bipolar devices.
(3) The source and drain of some FETs can be used interchangeably, and the gate voltage can also be positive or negative, which is more flexible than transistors.
(4) The field effect transistor can work under the condition of very small current and very low voltage, and its manufacturing process can easily integrate many field effect transistors on a silicon wafer, so the field effect transistor is widely used in large-scale integrated circuits. has been widely used.
How Relays Work
First, the definition of relay
Relay is a kind of automatic control device that will change the output by jumping when the input (electricity, magnetism, sound, light, heat) reaches a certain value.
Second, the relay characteristics of the relay
The input signal x of the relay increases continuously from zero to the action value xx when the armature starts to pull in, and the output signal of the relay jumps from y=0 to y=ym immediately, that is, the normally open contact changes from off to on. Once the contact is closed, the input quantity x continues to increase, and the output signal y will no longer change. When the input quantity x drops from a value greater than xx to xf, the relay begins to release, and the normally open contact is disconnected (as shown in Figure 1). We call this characteristic of the relay the relay characteristic, also called the input-output characteristic of the relay.
The ratio of the release value xf to the action value xx is called the feedback coefficient
That is, Kf=xf/xx
The ratio of the control power Pc output on the contact to the minimum power PO absorbed by the coil is called the control coefficient of the relay
That is Kc=PC/PO
Classification of relays
There are many classification methods of relays, which can be classified according to the principle of action, external dimensions, protection characteristics, contact load, product use, etc.
1. According to the principle of action
1. Electromagnetic Relay
Under the action of the current in the input circuit, a relay that produces a predetermined response by the relative movement of the mechanical parts. It includes DC electromagnetic relays, AC electromagnetic relays, magnetic latching relays, polarized relays, reed relays, and energy-saving power relays.
(1). DC electromagnetic relay: the electromagnetic relay whose control current in the input circuit is DC.
(2) AC electromagnetic relay: an electromagnetic relay whose control current in the input circuit is AC.
(3) Magnetic Latching Relay: After the magnetic steel is introduced into the magnetic circuit, after the relay coil is de-energized, the armature of the relay can still remain in the state when the coil is energized, with two stable states.
(4) Polarized relay: A DC relay whose state changes depending on the polarity of the input excitation.
(5) Reed relay: a relay that uses the action of a reed sealed in the tube and has the dual functions of a contact reed and an armature magnetic circuit to open, close or switch circuits.
(6) Energy-saving power relay: The control current in the input circuit is an AC electromagnetic relay, but its current is large (generally 30-100A), small in size, and power-saving function.
2. Solid State Relay
A relay whose input and output functions are completed by electronic components without mechanical moving parts.
3. Time relay
When the input signal is added or removed, the output part needs to delay or limit the time to close or open the relay of its controlled circuit until the specified time.
4. Temperature relay
A relay that operates when the outside temperature reaches a specified value.
5. Fan speed relay
When the wind speed reaches a certain value, the controlled circuit will be turned on or off.
6. Acceleration relay
When the acceleration of the moving object reaches the specified value, the controlled circuit will be turned on or off.
7. Other types of relays
Such as photorelays, acoustic relays, thermal relays, etc.
Second, the relay size classification
Miniature relays whose longest side dimension is not more than 10mm
Subminiature relays whose longest side dimension is greater than 10mm, but not greater than 25mm
Small relays whose longest side dimension is greater than 25mm, but not greater than 50mm
Three, relay contact load classification
Micropower relays are less than 0.2A relays.
Weak power relay 0.2~2A relay.
Medium power relay 2~10A relay.
High-power relays above 10A.
Energy saving power relay 20A-100A relay.
4. Classification of relay protection features
Sealed relays use welding or other methods to seal contacts and coils in a metal cover, and have a low leakage rate.
The plastic-encapsulated relay adopts the method of encapsulation to seal the contacts and coils in the plastic cover, and its leakage rate is relatively high.
A dust cover relay is a relay that protects the contacts and coils with a cover.
Open relays Relays that do not use protective covers to protect contacts, coils, etc.
Five, relay use classification
name definition
Communication relays (including high-frequency relays) The load range of this type of relay contacts is from low level to medium current, and the environmental conditions are not high.
Machine tool relays The relays used in machine tools have large contact load power and long life.
Relays for household appliances The relays used in household appliances require good safety performance.
Relays used in automobiles. These relays have high switching load power and high shock and vibration resistance.
Working principle of solid state relay
Solid State Relays (SSR for short) is a non-contact electronic switch composed of discrete components, membrane fixed resistor networks and chips, assembled by a mixed process to realize the electrical connection between the control circuit (input circuit) and the load circuit (output circuit). Isolation and signal coupling, the on-off switching function of the load is realized by a solid device, and there are no moving parts inside. Although there are many models and specifications of solid state relays on the market, their working principles are basically similar. It is mainly composed of three parts: input (control) circuit, drive circuit and output (load) circuit.
The input circuit of the solid state relay is to provide a loop for the input control signal, making it the trigger signal source of the solid state relay. The input circuit of the solid state relay is mostly DC input, and some are AC input. The DC input circuit is further divided into resistive input and constant current input. The input control current of a resistive input circuit varies linearly and positively with the input voltage. In the constant current input circuit, when the input voltage reaches a certain value, the current will no longer increase significantly with the increase of the voltage. This relay can be applied to a wide range of input voltages.
The drive circuit of the solid state relay can include three parts: an isolation coupling circuit, a functional circuit and a trigger circuit. Isolation coupling circuit, at present, two circuit forms of optocoupler and high frequency transformer are mostly used. Commonly used optocouplers are photo-transistor, photo-triac, photo-diode array (photo-volt) and so on. The high-frequency transformer coupling is to form a self-excited oscillation of about 10MHz under a certain input voltage, and transmit the high-frequency signal to the secondary of the transformer through the transformer core. The functional circuit can include various functional circuits such as detection and rectification, zero-crossing, acceleration, protection, and display. The function of the trigger circuit is to provide a trigger signal to the output device.
The output circuit of the solid state relay realizes the on-off switching of the solid state relay under the control of the trigger signal. The output circuit is mainly composed of an output device (chip) and an absorption loop that acts as a transient suppressor, and sometimes a feedback circuit is also included. At present, the output devices used in various solid state relays mainly include transistors (Transistor), thyristor (Thyristor or SCR), triac (Triac), MOS field effect transistor (MOSFET), insulated gate bipolar Transistor (IGBT) etc.
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