The resistor is a current limiting element.
The resistor is a current limiting element. After the resistor is connected in the circuit, it can limit the current through the branch it is connected to. The resistor with fixed resistance value is generally two pins, and the one with constant resistance value is called fixed resistor. Those with variable resistance are called potentiometers or variable resistors.
Classification and Application of Common Resistors
1、 Classification according to volt ampere characteristics:
a. Linear resistance: at a certain temperature, its resistance almost remains unchanged and is a certain value;
B. Nonlinear resistance: the resistance of some materials changes obviously with the change of current (or voltage). Its volt ampere characteristic is a curve. Under the action of a given voltage (or current), the ratio of voltage to current is the static resistance at the operating point, and the slope on the volt ampere characteristic curve is the dynamic resistance.
2： Classification according to resistance characteristics:
a. Fixed resistance and variable resistance: variable resistance (such as sliding rheostat) with adjustable resistance value; Fixed resistance (fixed value resistance) is not adjustable;
b. Special resistance (sensitive resistance): it is sensitive to physical environmental factors (such as temperature, humidity, light, voltage, mechanical force, and gas concentration); The resistance value will change with the change of physical quantity, showing different resistance values. The common ones are thermistor, photosensitive resistor, humidity sensitive resistor and varistor.
c. Non inductive resistance: It is commonly used as a load to absorb unnecessary electricity generated during the use of the product, or to buffer and brake. Such resistance is often called JEPSUN braking resistance or Jiebixin load resistance. It protects the frequency converter; It can be used in some precision instruments, electronic industrial equipment, etc;
d. Fuse resistance (fuse resistance): It is a special element with dual functions of resistor and fuse. When the circuit fails and its power exceeds the rated power, it will fuse like a fuse to disconnect the protection circuit. It is mainly used in the power circuit of color TV sets, video recorders and testing instruments.
3： Classification by material:
1. Alloy type: precision wire wound resistance, power wire wound resistance, precision alloy foil resistance;
a. Precision wire winding resistance: it is made of high resistance alloy wire wound on the insulating framework, and coated with heat-resistant glaze insulating layer or insulating paint. Features: stable, heat and corrosion resistant, low temperature coefficient, high resistance accuracy
b. Power type wire wound resistance: use alloy resistance wire with large resistance (such as nickel, chromium, iron, etc.) to wrap it on the non alkaline heat-resistant porcelain piece, and add heat-resistant, moisture resistant, non corrosive materials to protect it, then put it into the porcelain frame, and fill it with special incombustible heat-resistant cement for sealing. Therefore, it is also commonly known as cement resistance; It is characterized by accurate resistance, low noise, good heat dissipation and can withstand large power consumption. It is mostly used in the power stage of amplifiers. But because of the high cost, inductance is not suitable for high frequency circuits;
c. Precision alloy foil resistance: a special metal foil material is pasted on the ceramic substrate, and then the metal foil is carved into continuous lines by chemical etching or laser etching technology to form resistors with different resistance values, which are led out by pins and then packaged. Due to the complex process, the cost is high. It mainly applies military products, high-precision measurement products, etc; The metal foil is 100 times thicker than the film, with higher heat resistance and more advantages in anti-static.
2. Film type: metal film resistor, metal oxide film resistor, carbon film resistor;
a. Metal film resistor (commonly used as the symbol RJ): It is made 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. It is characterized by wide temperature range of working environment, low noise and small volume; It is usually widely used in circuits with high stability requirements. For example: advanced audio equipment, computers, instruments, national defense and space equipment, etc
b. Metal oxide film resistor (usually marked by the symbol RY): It is made by plating a layer of tin oxide on the porcelain tube and depositing a layer of metal oxide on the insulating rod. As it is also an oxide, it is stable under high temperature, resistant to heat shock and has strong load capacity. Its typical characteristics are that the metal oxide film and ceramic matrix are more firmly combined, and the load power of the resistance film is high. Strong acid and alkali resistance, salt fog resistance, suitable for working in harsh environments.
c. Carbon film resistor (commonly marked by the symbol RT): It is made by plating a layer of carbon on the porcelain tube and depositing crystalline carbon on the ceramic rod skeleton. This resistance has a wide range (10 Ω~10M Ω); The rated power is 1/8W~10W, and its biggest feature is low cost. In addition, it also has the advantages of stable performance, wide resistance range, low temperature coefficient and voltage coefficient, so it is the earliest and most widely used film resistor at present. Its appearance is usually green paint.
3. Synthetic type: solid carbon resistance, metal glass glaze resistance;
Solid carbon resistance: It is made by mixing carbon granular conductive material, filler and adhesive and implanting wires therein. The resistance value is affected by the proportion of toner and the thickness of carbon rod; It is characterized by its low price, but its resistance error, noise, and poor stability are rarely used at present.