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Let me show you the internal structure of mainstream resistors, which many people don't know

Resistors are generally directly called resistors in daily life. It is a current limiting element. After connecting the resistor in the circuit, the resistance value of the resistor is fixed, usually two pins, which can limit the current through the branch connected to it.   Those whose resistance cannot be changed are called fixed resistors. Those with variable resistance are called potentiometers or variable resistors. The ideal resistor is linear, that is, the instantaneous current passing through the resistor is proportional to the applied instantaneous voltage. Variable resistor for voltage division. On the exposed resistor, one or two movable metal contacts are pressed tightly. The contact position determines the resistance between either end of the resistor and the contact.   According to the classification of materials, resistors can be basically divided into five types of resistors, including wire wound resistors, carbon synthetic resistors, carbon film resistors, metal film resistors and metal oxide film resistors. I will show you the internal structure of mainstream resistors through five kinds of resistors.   Wire wound resistors are made by winding resistance wires. Resistors are made by winding high resistance alloy wires on the insulation skeleton, and are coated with heat-resistant glaze insulation layer or insulating paint. Winding resistance has low temperature coefficient, high resistance accuracy, good stability, heat resistance and corrosion resistance. It is mainly used as precision high-power resistance. Its disadvantages are poor high-frequency performance and large time constant.   First of all, the wire wound resistor is to wind the nickel chromium alloy wire on the alumina ceramic substrate, and control the resistance circle by circle. The winding resistance can be made into a precision resistance with a tolerance of 0.005%. At the same time, the temperature coefficient is very low. The disadvantage is that the parasitic inductance of the winding resistance is relatively large and cannot be used in high frequency. The volume of the wound resistor can be made very large, and then add an external radiator, which can be used as a high-power resistor.   Secondly, the carbon synthetic resistor is made of carbon and synthetic plastic. The concentration of carbon powder determines the resistance value. Tin plated copper leads are added at both ends, and finally packaged.   The carbon film resistor is made by plating a layer of carbon on the ceramic tube and depositing the crystalline carbon on the ceramic rod skeleton. Carbon film resistor is the most widely used resistor at present because of its low cost, stable performance, wide resistance range and low temperature coefficient and voltage coefficient.   In order to control the resistance more accurately, spiral grooves can be machined on the carbon film. The more spirals, the greater the resistance; Finally, metal leads are added, and resin packaging is formed. The process of carbon film resistor is a little more complicated, and it can be used as a precision resistor. However, due to the carbon quality, the temperature characteristic is still not very good.   The metal film resistor is formed by coating a layer of metal on the ceramic tube, and the alloy material is evaporated on the surface of the ceramic rod skeleton by vacuum evaporation. Compared with carbon film resistance, metal film resistance has higher accuracy, better stability, lower noise and temperature coefficient. It is widely used in instruments and communication equipment.   Finally, the metal oxide film resistor is formed by plating a layer of tin oxide on the porcelain tube and depositing a layer of metal oxide on the insulating rod. Because it is an oxide itself, it is stable at high temperature, resistant to heat shock, and has strong load capacity. According to its purpose, it has general purpose, precision, high frequency, high voltage, high resistance, high power and resistance network.

What are the categories of memory products?

memorizer is an electronic device that uses semiconductors, memorizer media and other technologies to store data. Memory unit is actually a kind of sequential logic integrated circuit. They can be divided into read-only memory (ROM) and random access memory (RAM) according to the type of memory used. They have different functions and therefore different descriptions.   Semiconductor devices and magnetic materials are the main storage media for memory. The smallest unit of storage in a memory is a bistable semiconductor circuit or a CMOS transistor or magnetic material that stores a binary code. A storage unit consists of several storage units, and then a storage unit consists of many storage units.   There are several different ways to categorize products for storage. According to the function of memory in computer system, it can be divided into main memory, auxiliary memory, cache memory, control memory, etc. In order to resolve the contradiction between the requirement of large capacity, fast speed and low cost for memory, multilevel memory architecture is usually used, even with high-speed buffer memory, main memory and external memory.   By storage media, mainly include:   (1) Semiconductor memory: A memory consisting of semiconductor devices. The U disk is a semiconductor memory. The Flash chip is integrated in the U disk, and the storage medium is a semiconductor.   (2) Magnetic surface memory: a memory made of magnetic material.   By storage method, it mainly includes:   (1) Random memory: The contents of any storage unit can be accessed randomly, regardless of the access time or the physical location of the storage unit.   Sequential memory: can only be accessed in a certain order, the access time is related to the physical location of the storage unit.

What is the common impedance induction of RFI component interference path

RFI component is the abbreviation of anti RF interference component. RF interference is the interference generated at or very close to the signal frequency received by the receiver. The Federal Communications Commission (FCC) of the United States has formulated RF interference standards for electronic equipment to minimize this interference.   RFI components generally include RFI gaskets, common mode chokes, ferrite beads and other products.   Interference voltage will be generated when interference current flows through impedance Z. The interference voltage caused by common impedance induction is divided into the following categories:   First of all, from the internal circuit layout and ground wire design of the equipment, when a power supply supplies several circuits, the output current of the high-level circuit will flow into the power supply in whole or in part, resulting in interference. For high frequency, the output impedance of the power supply and the distributed inductance of the power lead can cause interference.   Similarly, when there is high-frequency current on the grounding system inside the equipment, there will be the problem of converting the impedance of the grounding system into voltage. When it forms a part of the input circuit of the low-level signal amplifier, the voltage of the grounding system will be amplified and output in the form of interference.   Secondly, from the perspective of shared power supply and grounding wire, when several devices and RF devices are powered by the same AC power supply, the high-frequency current generated by the RF device is converted into interference voltage to other devices through the impedance Z of the shared power supply, and it should be transmitted through the power source line.   It should also be noted that if each equipment uses a common wiring as the grounding wire, mutual interference will inevitably occur when there is a large current flowing on the common grounding wire.  

How Operational Amplifiers Work

An operational amplifier can be thought of as a simple box or block containing an amplifying device, such as a bipolar transistor, a field effect transistor, or an operational amplifier, which has two inputs and two outputs (grounded), the output signal being much larger than the input signal because it has been "amplified".   Operational amplifier has two power supply modes, dual power supply and single power supply. For an operation with dual power supply, the output value can be changed up or down at zero voltage, or the output can be set to zero at zero differential input voltage. For single-supply operation, the output value is only allowed to change within a certain range between the power supply and the ground.   For general Operational Amplifiers, the input potential is required to be in the range from a certain value above the negative power supply to a certain value below the positive power supply, but it can also be changed from a negative power supply to a positive power supply in the whole range after special design, even slightly higher or lower than the positive power supply. This kind of operation amplifier is called track-to-track input Operational Amplifier.   operational amplifier are generally considered to have the following characteristics:   Infinite open-loop gain G = V out / V in   The input impedance R in is infinite, so the input current is zero   Zero Input Misalignment Voltage   Infinite output voltage range   Infinite bandwidth with zero phase shift and infinite swing rate   Zero output impedance R out   Zero noise   Infinite common mode rejection ratio (CMRR)   Infinite power rejection ratio.