(Classic) Design Experience Notes for Electronic Engineers

Operational amplifiers are widely used in analog and digital circuits through simple peripheral components. There are several types of operational amplifiers, with several differences in detailed performance parameters, but the principles and application methods are the same.

An operational amplifier usually has two input terminals, namely the positive input terminal and the negative input terminal, and one and only one output terminal. In addition to the two inputs and one output, some operational amplifiers also have several compensation pins to improve performance.

The resistance of a photoresistor changes significantly with the intensity of light, so it can be used to make smart curtains, automatic street light switches, automatic camera shutter time adjusters, etc.

Reed switch is an electronic component that can control the on and off of a circuit through a magnetic field. The inside of the reed switch is composed of a soft magnetic metal reed. In the presence of a magnetic field, the metal reed can gather magnetic lines of force and act on them, thereby achieving the effect of switching on or off.

Essential Basic Knowledge for Electronic Engineers (Part 2)

The function of a capacitor can be described in three words: "charge and discharge." Don't underestimate these three words. Because of these three words, capacitors can pass alternating current and block direct current; pass high-frequency alternating current and block low-frequency alternating current.

The function of a capacitor can be described in eight words: "isolate direct current, pass alternating current, pass high voltage but reduce resistance." These eight words are derived from the three words "charge and discharge." It doesn't matter if you don't understand them, just memorize them first.

The filter capacitor can be selected according to the output current of the DC power supply and the requirements of the power supply of the subsequent stage (circuit or product). Under normal circumstances, 1000UF-4700UF is more appropriate for every 1 ampere of current.

Essential Basic Knowledge for Electronic Engineers (Part 3)

The role of inductance can be described in four words: "electromagnetic conversion." Don't underestimate these four words. Because of these four words, inductance can block AC and pass DC; pass low-frequency AC and block high-frequency AC. The role of inductance can be described in eight words: "block DC, pass low-frequency AC and block high-frequency AC." These eight words are derived from the three words "electromagnetic conversion."

Inductors are the mortal enemy of capacitors. In addition, inductors have another characteristic: current and magnetic field must exist at the same time. If the current disappears, the magnetic field will disappear; if the magnetic field disappears, the current will disappear; if the north and south poles of the magnetic field change, the positive and negative poles of the current will also change.

The current and magnetic field inside the inductor are always "fighting a civil war". The current wants to change, but the magnetic field won't let it; the magnetic field wants to change, but the current won't let it. However, due to external reasons, both the current and the magnetic field may have to change. When voltage is added to the inductor coil, the current wants to increase from zero, but the magnetic field will oppose it, so the current has to increase slowly; when voltage is removed from the inductor, the current wants to change from large to zero, but the magnetic field will oppose it again. However, the current loop is gone, and the current has been forced to zero. The magnetic field will get angry and immediately generate a very high voltage at both ends of the inductor, trying to generate current and keep the current unchanged. This voltage is very high and can even damage electronic components. This is the self-inductance phenomenon of the coil.

When a changing magnetic field is applied to an inductor coil, the coil will generate current as long as there is a closed loop. If there is no loop, a voltage will be generated at both ends of the coil. The purpose of generating voltage is to generate current. When two or more coils share a magnetic core (to gather magnetic lines of force) or a magnetic field, the current and magnetic field between the coils will affect each other, which is the mutual induction phenomenon of current.

As you can see, an inductor is actually a wire. The resistance of an inductor to direct current is very small, even negligible. The inductor presents a large resistance effect to alternating current.

The series and parallel connection of inductors is very complicated, because inductors are actually wires distributed along a certain route. Therefore, the series and parallel connection of inductors is also related to the position of the inductors (mainly related to the interaction of magnetic fields). If the effects of magnetic field, distributed capacitance, wire resistance (Q value), etc. are not considered, it is equivalent to the series and parallel connection of resistors.

The higher the frequency of the alternating current, the greater the resistance of the inductor. The lower the frequency of the alternating current, the smaller the resistance of the inductor.

When an inductor and a fully charged capacitor are connected in parallel, the capacitor will discharge to the inductor, the inductor will generate a magnetic field, the magnetic field will maintain the current, the current will reverse charge the capacitor, and after reverse charging it will discharge again, and this cycle will repeat over and over again... If there is no loss, or this loss can be replenished in time, a stable oscillation will occur.

Essential Basic Knowledge for Electronic Engineers (IV)

Coupling means to transfer signals. Photocouplers are naturally components that use light to transfer electrical signals. They usually refer to electronic components that have a light-emitting part and a receiving part that are made in one piece. Usually four effective pins (i.e. four pins that are connected to the circuit and work) form a group.

The advantage of optocouplers is that they can easily achieve power isolation, and are most commonly used in primary and secondary isolation of switching power supplies using AC power. In addition, they are also widely used in computer peripheral communications, and multiple groups of optocouplers (each group has at least four pins) can be integrated into one component.

Piezoelectric ceramics can be used as excellent vibration detectors. They are electroacoustic devices that can produce sound when an audio voltage is applied and can induce a weak voltage when vibrated (produces mechanical deformation).

When welding, properly adjust the welded part, the soldering iron tip, and the solder wire (with flux) to make the three points come together and fully contact. When the welded part has proper solder and flux, the solder wire should be removed. The welding process is usually controlled within 2-3 seconds.

Soldering flux: Rosin water is often used as soldering flux in factories. You can make it yourself by dissolving rosin with industrial alcohol (medical alcohol is more expensive and unnecessary). Note: Do not mix too much at one time, and the concentration can be flexibly controlled.

Essential Basic Knowledge for Electronic Engineers (V)

The role and function of a diode can be described in four words: "unidirectional conduction." Diodes are often used for rectification, detection, voltage stabilization, clamping, circuit protection, etc.

A rectifier diode is connected in series in the power supply circuit of the Walkman. When the DC power supply is connected reversely, no current will be generated and the Walkman will not be damaged.

When a forward voltage lower than 0.6V is applied to a diode (silicon material), the diode basically generates no current (it is even less likely to generate current in the reverse direction). This voltage is called dead zone voltage, threshold voltage, threshold voltage, turn-on voltage, etc.

The role and function of the transistor can be completed by four words: "variable resistance." Since the resistance value equivalent to the transistor can change indefinitely, the transistor can be used to design switching circuits, amplification circuits, and oscillation circuits.

The collector current of the transistor is equal to the base current multiplied by the amplification factor. When the base current reaches a certain level, the collector current cannot increase any further due to various reasons. At this time, the collector voltage is equal to or close to the emitter voltage, which is equivalent to the resistance value becoming 0 ohms.

The trick to ensure the amplification state of the transistor is: the emitter junction is forward biased and the collector junction is reverse biased.

The triode is a current-controlled device, and the field-effect tube is a voltage-controlled device. The field-effect tube has excellent performance, but among discrete components, its adaptability to low power supply voltage is worse than that of the triode.

Field effect transistors are voltage-controlled devices and are easily damaged by static electricity. Therefore, most field effect transistors have protection diodes.

The thyristor is actually a high-speed electronic switch without mechanical contacts. This switch needs to be controlled by a small current. This switch has a self-locking function, that is, after it is turned on, it can still be turned on when the control current is removed, and once it is turned off, it can maintain the off state.

Essential Basic Knowledge for Electronic Engineers (VI)

Resistors are usually marked with color rings. The color ring method uses brown, red, orange, yellow, green, blue, purple, gray, white, and black to represent the ten Arabic numerals 1234567890. Gold and silver represent the ratio of 0.1, 0.01 or the error of 5%, 10%. The kit comes with a real color sample and a variety of color ring resistors.

The common four-color ring needs to read three significant digits, the first and second digits represent the significant digits, and the third digit represents the magnification. For example: yellow, purple, red and gold, the three significant digits are 472, which means 47 times 102 (or adding two zeros) equals 4700, which is 4.7K ohms; another example: brown, black, black and gold, the three significant digits are 100, which means 10 times 100 (or adding 0 zeros) equals 10, which is 10 ohms.

During the experiment, if there is no unidirectional conduction characteristic between the base and other pins of the transistor (or the unidirectional conduction characteristic is not obvious), it means that the transistor is bad; in addition, even if the unidirectional conduction characteristic is normal, but it cannot be controlled by the base or is unstable, it also means that the transistor is bad or has poor performance.

When a proper trigger current is added to the control electrode of the thyristor, the thyristor can change from the off state to the on state. At this time, we cancel the trigger current of the control electrode, but the thyristor can still maintain the on state. If the current flowing through the thyristor starts to decrease, when it is less than the ability to maintain conduction, the thyristor will turn off and will not turn on until the next trigger.

Essential Basic Knowledge for Electronic Engineers (VII)

As early as more than 2,000 years ago, people discovered the phenomena of electricity and magnetism. my country invented the Sinan as early as the Warring States Period (475-211 BC). However, the real understanding and widespread application of electricity and magnetism by humans have only a history of more than 100 years. Driven by the wave of the first industrial revolution, many scientists have conducted in-depth and detailed research on electricity and magnetism, and have made significant progress. People have found that charged objects repel each other with the same charge and attract each other with opposite charges, which is similar to the phenomenon of magnetism.

In 1785, French physicist Coulomb proposed what later generations called "Coulomb's law" based on his predecessors' understanding of electromagnetic phenomena, which unified electrical and magnetic phenomena.

In 1800, Italian physicist Volta developed a chemical battery and obtained a continuous battery by artificial means, creating the primary conditions for future generations to study the relationship between electricity and magnetism.

In 1822, based on the extensive work done by his predecessors, Faraday of Britain proposed the law of electromagnetic induction, proving that "magnetism" can generate "electricity", which laid the foundation for the principles of generators and motors.

In 1837, American painter Morse designed a more practical telegraph machine that used code to transmit information based on the work of his predecessors. Later, he established the world's first telegraph line between Washington and Baltimore.

In 1876, Bell of the United States invented the telephone, realizing the earliest analog communication of mankind. Based on the summary of the work of his predecessors, Maxwell of the United Kingdom proposed a complete set of "electromagnetic theory", which is expressed as four differential equations. This is what later generations called the "Maxwell equations". Maxwell concluded that moving electric charges can generate electromagnetic radiation, forming invisible electromagnetic waves that gradually propagate outward. Although he did not propose the term "radio", his electromagnetic theory has already told people that "electricity" can be transmitted "wirelessly".