Basic Knowledge of Electronic Components.doc

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Basic Knowledge of Electronic Components I: Resistors Resistance, whose English term is resistance, is usually abbreviated as R. It is a fundamental property of conductors, and it depends on the size, material, and temperature of the conductor. Ohm’s law states that I=U/R; therefore, R=U/I. The basic unit of resistance is the ohm, denoted by the Greek letter “Ω”. It is defined as the resistance value corresponding to one ampere of current flowing when a voltage of one volt is applied across a conductor. The main function of a resistor is to prevent current from flowing through it. In fact, “resistance” refers to a property, whereas in electronic devices, resistance usually denotes a component such as a resistor. The master said to the apprentice, “Find a 100-ohm resistor!” ”It refers to a resistor with a \"resistance value\" of 100 ohms; the unit ohm is often abbreviated as Ω. Other common units used to express resistance values are kiloohms (kΩ) and megaohms (MΩ). 　　1. Types of resistors There are many types of resistors, which are generally divided into three main categories: fixed resistors, variable resistors, and special resistors. In electronic products, fixed resistors are the most widely used. Fixed resistors can be further divided into many categories based on their manufacturing materials; among the most commonly used ones are RT-type carbon film resistors, RJ-type metal film resistors, RX-type wire-wound resistors, as well as sheet resistors which have become widely used in recent years. The model naming follows a consistent pattern: R stands for resistance, T for carbon film, J for metal, and X for wire-wound, which are the first letters of their pinyin names. In old domestic electronic devices, resistors with a green coating on their surface can often be seen; those are of the RT type. And the red-colored resistor is of the RJ type. In traditional electronic devices, resistors are usually green in color. Why? This relates to the issue of product cost, as although metal film resistors offer high precision and good temperature characteristics, their manufacturing cost is also high. On the other hand, carbon film resistors are particularly inexpensive and can meet the requirements of consumer products. ? ? Resistors also have different power ratings, of course. Commonly used are 1/8 watt \"color-band carbon film resistors\", which are the most frequently used in electronic products and electronics manufacturing. Of course, in some miniature products, 1/16 watt resistors are used, which are much smaller in size. Another type is the micro-sheet resistor, which belongs to the family of surface-mount components. It was previously found mainly in imported micro-products, but now electronics enthusiasts can also purchase them (for wireless spying?) 2. Marking of resistors 　　 These resistors with direct markings make it easy to identify their specifications when they are newly purchased. However, when assembling electronic products, it is necessary to consider ease of future maintenance by orienting the labeled surfaces in areas that are easy to see. So special attention must be paid when bending the feet. During manual assembly, having this extra step isn’t a big problem, but the machines on automated production lines aren’t that smart. Moreover, as resistor components become smaller, the markings printed on them become difficult to read. Therefore, the “color ring marking method” is commonly used internationally. In fact, \"color-coded resistors\" hold a dominant position among resistor components. “As the name suggests, a color-coded resistor uses different colored rings on it to indicate the resistance value. Some are represented by 4 color rings, while others use 5. Is there a difference? Yes. 4-band resistors are usually carbon film resistors; 3 color bands are used to indicate the resistance value, while 1 color band is used to indicate the tolerance. 5-band resistors are generally metal film resistors; to better indicate precision, the resistance value is represented by 4 color bands, with another band used to indicate the error. The table below shows the color-to-digit correspondence for color-coded resistors: Color Valid digits Multiplier Allowable tolerance Black 0 10 to the power of 0 Brown 1 10 to the power of 1 +/- 1% Red 2 10 to the power of 2 +/- 2% Orange 3 10 to the power of 3 ----- Yellow 4 10 to the power of 4 ----- Green 5 10 to the power of 5 +/- 0.5% Blue 6 10 to the power of 6 +/- 0.2% Purple 7 10 to the power of 7 +/- 0.1% Gray 8 10 to the power of 8 ----- White 9 10 to the power of 9 +5%~-20% No color ----- ----- +/- 20% Silver ----- ----- +/- 10% Gold ----- ----- +/- 5% The rule for color-coded resistors is that the last ring indicates the tolerance; for four-ring resistors, the first two rings represent the significant digits, while the third ring indicates the power to which 10 is raised. Don’t be afraid; just remember the colors and numbers, there’s no need to remember anything else. There is a trick: when facing a color-coded resistor, identify the gold or silver end and place it facing down, then start reading the color codes from the beginning. For example, if the first ring is brown, the second ring is black, the third ring is red, and the fourth ring is gold, then its resistance value is 1, 0; the number of zeros added corresponds to the third ring. In this case, 2 zeros are added, so the actual resistance value is 1000Ω, or 1kΩ. 　　3. Variable resistor A variable resistor is also known as a potentiometer; the volume control potentiometer on electronic devices is an example of a variable resistor. However, potentiometers are generally considered to be manually adjustable, while variable resistors are usually smaller and installed on circuit boards where they are not adjusted frequently. A variable resistor has three pins, and the resistance value between two of these pins is fixed; this resistance value is what is referred to as the resistor’s resistance value. The resistance value between the third pin and any two of the other pins can change as the arm of the shaft rotates. In this way, the voltage or current in the circuit can be adjusted to achieve the desired control effect. 　　 A potentiometer can also be understood as a variable resistor with a adjustable resistance value, but it is different from a variable resistor; potentiometers have three or more terminals. The main function of a potentiometer is to adjust the values of various signals or voltages. In addition to being used in the different circuit boards within a computer, it is also widely employed in many devices – from color displays to active multimedia speakers, virtually all devices contain potentiometers. Under normal circumstances, it is best not to touch the potentiometers in the circuit (with the exception of various adjustment knobs outside the device), especially those in the power supply section, as there are many values that cannot be adjusted to their optimal levels manually. Of course, if a replacement is necessary due to damage, that’s a different situation, but it’s still important to use a potentiometer of the same specification and adjust it to similar settings as the original one before testing the device; this will provide greater reliability. Additionally, the materials used in the manufacture of potentiometers vary as well; they can be broadly divided into three categories: metal-film potentiometers, synthetic carbon potentiometers, and metal-glass glaze potentiometers. 　　Note: In circuits, the symbol for a potentiometer is “W”. 　　4. Special resistors A photoresistor is a component whose resistance value changes depending on the intensity of external light (i.e., brightness); the stronger the light, the lower the resistance, and the weaker the light, the higher the resistance. Its shape and circuit symbols are shown in Figure 2. If the two terminals of the photosensitive resistor are connected to the test leads of a multimeter, and the resistance value of the photosensitive resistor is measured using the R×1k setting on the multimeter under different lighting conditions: by moving the photosensitive resistor from a dark environment to sunlight or a light source, the reading on the multimeter will change. In complete darkness, the resistance value of a photosensitive resistor can exceed several megohms (the multimeter indicates an infinite resistance, meaning the pointer does not move), while in strong light, the resistance value can drop to a few thousand ohms or even below 1 kiloohm. 　　Taking advantage of this property, various light-controlled small circuits can be created. In fact, most street lights are automatically controlled by light-sensitive switches, and one of the key components in these switches is a photosensitive resistor (or a photosensitive triode, a semiconductor component with similar functions that provides amplification). A photosensitive resistor is made by depositing a layer of cadmium sulfide (CdS) film on a ceramic substrate; it is essentially also a semiconductor component. In the new village, the voice-controlled hallway lights do not turn on during the day, and this is also due to the action of the photosensitive resistor. We can use it to make an electronic rooster that crows at dawn. 　　A thermistor is a special semiconductor device whose resistance value changes depending on the temperature of its surface. It was originally used to ensure that electronic devices could function properly at different ambient temperatures, and this is known as temperature compensation. New computer motherboards all come equipped with CPU temperature monitoring and over-temperature alarm functions, which make use of thermistors. 2. Capacitors: Various types of capacitors are needed in electronic manufacturing, and they each perform different functions within circuits. Similar to resistors, it is commonly referred to simply as a capacitor, denoted by the letter C. As the name implies, a capacitor is a “container for storing charge.” Although there are many types of capacitors, their basic structure and principle remain the same. A capacitor is formed when two pieces of metal that are close to each other are separated by some substance (solid, gas, or liquid). The two pieces of metal are called electrodes, and the substance in between is called the dielectric. Capacitors are also divided into those with fixed capacitance and those with variable capacitance. But capacitors with a fixed capacity are common, with electrolytic and ceramic capacitors being the most frequent types. 　　 Different capacitors have varying capacities to store charge. It is specified that the amount of charge stored in a capacitor when a 1-volt direct current voltage is applied to it is defined as the capacitance of that capacitor. The basic unit of capacitance is the farad (F). But in reality, the farad is a unit that is not very commonly used, as the capacitance of capacitors is usually much smaller than 1 farad. Units such as microfarads (μF), nanofarads (nF), and picofarads (pF) are more frequently used. The relationships between these units are as follows: 1 farad (F) = 1,000,000 microfarads (μF); 1 microfarad (μF) = 1,000 nanofarads (nF) = 1,000,000 picofarads (pF). In electronic circuits, capacitors are used to allow alternating current to pass while blocking direct current, and they are also used to store and release charge in order to function as filters and smooth out pulsating output signals. Small-capacity capacitors are typically used in high-frequency circuits, such as radios, transmitters, and oscillators. Capacitors with large capacity are often used for filtering and storing charge. There is another characteristic as well: generally, capacitors of 1μF or more are electrolytic capacitors, while those below 1μF are mostly ceramic capacitors. Of course, there are other types as well, such as monolithic capacitors, polyester capacitors, and low-capacity mica capacitors. Electrolytic capacitors have an aluminum casing filled with an electrolyte, and they have two electrodes that serve as the positive (+) and negative (–) terminals. Unlike other capacitors, their polarity in a circuit must not be reversed; other capacitors, on the other hand, do not have a polarity. 　　 When the two electrodes of a capacitor are connected to the positive and negative terminals of a power supply, even after the power supply is disconnected, there is still residual voltage between those two terminals (this can be observed using a multimeter in the tutorials that follow); we say that the capacitor has stored charge. A voltage is established between the capacitor plates, storing electrical energy; this process is known as charging the capacitor. A fully charged capacitor has a certain voltage across its terminals. The process by which the charge stored in a capacitor is released into the circuit is called the discharge of the capacitor. 　　To give a real-life example, we see that in commercially available rectified power supplies, the LED on them continues to glow for a while after the plug is pulled out, before gradually going out; this is because the capacitor inside stores electrical energy in advance and then releases it. Of course, this capacitor was originally used for filtering. As for capacitive filtering, I wonder if you have ever used a rectified power supply with a portable audio player. Generally, low-quality power supplies use filter capacitors of smaller capacity to cut costs, which results in a humming sound in the headphones. At this point, an electrolytic capacitor with a larger capacity (1000μF; make sure the positive terminals are connected together) can be connected in parallel across the power supply, which generally improves the performance. When hobbyists build HiFi audio systems, they use capacitors with a capacitance of at least 10,000 microfarads for filtering purposes. The larger the filtering capacitor, the more the output voltage waveform approaches that of direct current. Moreover, the energy storage capability of large capacitors ensures that when sudden large signals arrive, the circuit has sufficient energy to produce a strong audio output. At this point, the function of the large capacitor is somewhat similar to that of a reservoir, allowing the originally turbulent water flow to be discharged smoothly and ensuring a steady supply when there is high demand for water downstream. 　　 In electronic circuits, current flows only during the charging process of a capacitor. Once charging is complete, the capacitor does not allow direct current to pass through it, thus serving the function of blocking direct current in the circuit. In electrical circuits, capacitors are often used for coupling, bypassing, filtering, etc., all by taking advantage of their property of allowing alternating current to pass while blocking direct current. So why can alternating current pass through a capacitor? Let’s first take a look at Communication 3: Diodes. Crystal diodes are commonly denoted in circuits using the letter “D” followed by a number; for example, D5 refers to the diode with number 5. 1. Function: The main characteristic of a diode is its unidirectional conductivity, meaning that under the influence of a forward voltage, its conductive resistance is very low ； Under reverse voltage, the on-resistance is extremely large or infinite. It is precisely because of these properties that diodes are commonly used in cordless telephones in circuits for rectification, isolation, voltage regulation, polarity protection, coding control, frequency modulation, and noise suppression. The crystal diodes used in telephones can be classified by function into: rectifier diodes (such as 1N4004), isolation diodes (such as 1N4148), Schottky diodes (such as BAT85), light-emitting diodes, voltage regulator diodes, etc. 　 2. Identification method: Identifying diodes is simple. The N pole (negative pole) of low-power diodes is usually marked with a colored ring on the outside of the diode. Some diodes use special symbols to indicate the P pole (positive pole) or the N pole (negative pole), while others employ symbols such as “P” and “N” to determine the polarity of the diode. The positive and negative poles of a LED can be identified by the length of its pins; the longer pin is the positive pole, and the shorter one is the negative pole. 　3. Precautions for testing: When using a digital multimeter to test a diode, connect the red probe to the positive terminal of the diode and the black probe to its negative terminal; the resistance value measured in this way represents the diode’s forward conduction resistance. This is the opposite of the probe connection method used with an analog multimeter. Zener diode 　Zener diodes are commonly denoted in circuits using “ZD” followed by a number; for example, ZD5 refers to the zener diode with number 5. 　　1. The voltage-regulating principle of voltage-regulating diodes: The characteristic of voltage-regulating diodes is that once they break down, the voltage across them remains essentially constant. In this way, once the Zener diode is connected to the circuit, if the supply voltage fluctuates or if voltage levels at various points in the circuit change for other reasons, the voltage across the load will remain essentially constant. 　 2. Fault characteristics: The faults of voltage-regulating diodes mainly manifest as open circuits, short circuits, and unstable voltage regulation values. Among these 3 types of faults, the first one is characterized by an increase in supply voltage ； The latter two types of faults are characterized by the power supply voltage dropping to zero volts or unstable output. 　The common models of voltage-regulating diodes and their corresponding voltage regulation values are listed in the table below:
Model: 1N4728, 1N4729, 1N4730, 1N4732, 1N4733, 1N4734, 1N4735, 1N4744, 1N4750, 1N4751, 1N4761
Voltage Regulation Values: 3.3V, 3.6V, 3.9V, 4.7V, 5.1V, 5.6V, 6.2V, 15V, 27V, 30V, 75V

Varactor Diodes
Varactor diodes are a special type of diode designed based on the principle that the junction capacitance of a regular diode’s “PN junction” can change as a function of the applied reverse voltage. 　In cordless telephones, varactor diodes are primarily used in the high-frequency modulation circuits of mobile or landline phones to modulate low-frequency signals into high-frequency signals for transmission. In operation, the varactor modulation voltage is generally applied to the negative terminal, causing the capacitance of the varactor’s internal junction to change as the modulation voltage varies. 　　When a varactor diode fails, it is mainly manifested by leakage current or reduced performance: (1) When leakage occurs, the high-frequency modulation circuit will not function properly or its modulation performance will decline. 　　(2) When the varactor performance deteriorates, the operation of the high-frequency modulation circuit becomes unstable, resulting in distortion in the high-frequency signal after it is modulated and sent to the other party for reception. 　　When any of the above situations occurs, a varactor diode of the same model should be replaced. IV. Transistors: Structure and types of bipolar junction transistors. The bipolar junction transistor is one of the basic semiconductor components; it has the ability to amplify current and serves as a key element in electronic circuits. A transistor is formed by creating two PN junctions that are very close to each other on a single semiconductor substrate. These two PN junctions divide the semiconductor into three sections: the middle section is the base region, while the two sides are the emitter region and the collector region. There are two types of configurations: PNP and NPN. As shown in the diagram, corresponding electrodes are drawn from these three regions: the base b, the emitter e, and the collector c. 　　The PN junction between the emitter region and the base region is called the emitter junction, while the PN junction between the collector region and the base region is called the collector. The base region is very thin, while the emitter region is thicker and has a higher impurity concentration. In a PNP transistor, it is holes that are \"emitted\" from the emitter region; these holes move in the same direction as the current flow, hence the emitter arrow points inward ； The emitter region of an NPN transistor emits free electrons, and the direction in which these electrons move is opposite to the direction of the current; hence, the emitter arrow points outward. The emitter arrow points outward. The direction of the emitter arrow also indicates the conduction direction of the PN junction under forward voltage. Both silicon transistor and germanium transistor come in PNP and NPN types. 　　Packaging types and pin identification of transistors The common packaging types for transistors are metal packaging and plastic packaging. There is a certain pattern to the arrangement of their pins; as shown in the diagram, for low-power transistors with metal packaging, the pins are placed according to the positions indicated in the bottom view, such that the three pins form the vertices of an isosceles triangle, with e, b, and c arranged from left to right ； For low-to-medium power plastic transistors, align their plane toward you as shown in the diagram, with the three pins facing downward; from left to right, they are labeled e, b, and c. 　　Currently, there are many types of crystal transistors available in the domestic market, and their pin arrangements vary. When using a transistor whose pin arrangement is unknown, it is necessary to measure to determine the correct position of each pin, or consult the transistor’s user manual to understand its characteristics as well as the relevant technical parameters and information. 　　Current amplification of crystal transistors Crystal transistors possess current amplification capability; essentially, they are able to control a large change in the collector current using only a small change in the base current. This is the most basic and important characteristic of a transistor. We refer to the ratio of ΔIc/ΔIb as the current gain of the crystal transistor, denoted by the symbol “β”. The current gain is a constant value for a given transistor, but it can also change to some extent as the base current varies while the transistor is in operation. The three operating states of a crystal transistor: Cutoff state: When the voltage applied to the transistor’s emitter junction is less than the forward voltage of the PN junction, the base current is zero, and both the collector current and the emitter current are also zero. In this state, the transistor loses its ability to amplify current; the connection between the collector and the emitter functions as if it were an open switch. We refer to this state as the cutoff state of the transistor. 　　 Amplification mode: When the voltage applied to the transistor’s emitter junction is greater than the forward voltage of the PN junction and reaches a suitable value, the emitter junction is forward-biased while the collector junction is reverse-biased. In this state, the base current controls the collector current, enabling the transistor to exhibit current amplification; the current gain β is equal to ΔIc/ΔIb, and this is when the transistor is in the amplification mode. 　　 Saturation state: When the voltage applied to the transistor’s emitter junction is greater than the forward voltage of the PN junction, and when the base current increases to a certain level, the collector current no longer rises as the base current increases; instead, it remains relatively constant around a certain value. At this point, the transistor loses its current amplification capability, and the voltage between the collector and the emitter becomes very small, resulting in a conductive state similar to that of a switch between the collector and the emitter. This state of the transistor is what we call saturated conduction. 　　Based on the voltage levels of the various electrodes while the transistor is operating, it is possible to determine its operating state. Therefore, electronic repair technicians often use a multimeter to measure the voltage at each terminal of the transistor during repairs, in order to assess its performance and operating condition. Using a multimeter to test transistors 　　 Identifying the base of a transistor: Based on the schematic diagram of a transistor, we know that its base is the common terminal of the two PN junctions within it. Therefore, to identify the base of a transistor, one only needs to find the common terminal of those two PN junctions – that is the base of the transistor. The specific method is to set the multimeter to the R×1k setting on the resistance scale. First, place the red test lead on one of the transistor’s pins, and then use the black test lead to touch the other two pins of the transistor. If there is continuity in both attempts, then the pin where the red test lead is placed is the base of the transistor. If it is not found in one attempt, switch the red test lead to the other terminal of the transistor and test again twice ； If it still isn’t found, try a different red test lead and measure twice more. If it still isn’t found, then use the black test lead on one of the transistor’s pins, and use the red test lead to make two tests to check whether there is full conductivity; if it doesn’t work on the first try, try using the leads in reverse. In this way, up to 12 measurements can be taken, and the base will eventually be found. 　　 Identification of transistor types: There are only two types of transistors, namely PNP type and NPN type. To make the determination, it is sufficient to know whether the base is made of P-type material or N-type material. When using the R×1k setting on a multimeter, the black test lead represents the positive terminal of the power supply. If a connection is established when the black lead is connected to the base, it indicates that the base of the transistor is made of P-type material; in such a case, the transistor is of the NPN type. If the red test lead causes conduction at the base, it indicates that the transistor’s base is made of N-type material; in such a case, the transistor is of PNP type. 5. Switches Switches are a very common type of component, and they can be found in all kinds of devices. Strictly speaking, the jumpers on various circuit boards, as well as the buttons on keyboards and mice, also constitute switches. The author is unable to provide a detailed description of the classifications of switches here, as there are simply too many of them; therefore, the author roughly divides them into current-type switches and voltage-type switches. Voltage-type switches are used solely for controlling signal voltages, such as jumpers and the switches on keyboards and mice ； Current-type switches are used to control power supplies, such as the power switches on active speakers and those on multi-functional sockets. When these switches are closed, a large current flows through them; the sudden surge in current can generate sparks inside the switch, and these sparks can cause oxidation of the switch. Therefore, it is important not to repeatedly close and open current-type switches in order to ensure their long service life. 　　 Note: The symbol for a switch in a circuit is “S”.