Structure and characteristics of resistors

1. Structure and Characteristics of Carbon Film Resistors
Carbon film resistors are a type of film resistor. They are made by depositing a carbon film on a ceramic skeleton, using crystalline carbon produced by thermal decomposition of hydrocarbons under high temperature and vacuum. The resistance value is controlled by controlling the thickness of the carbon film and grooving the film. The outer surface of the resistor is typically coated with a green or orange protective varnish.
Carbon film resistors come in many varieties, depending on their application and characteristics. In addition to standard carbon film resistors, there are also RTL measurement-type carbon film resistors used in various measuring instruments, and carbon film resistors for high or ultra-high frequencies, such as RTCP rod-shaped ultra-high frequency carbon film resistors and RTCP-Q button-shaped ultra-high frequency carbon film resistors.
Carbon film resistors have the following characteristics:
① Excellent stability; voltage changes have minimal effect on resistance, and they have a negative resistivity.
② Excellent high-frequency characteristics, allowing them to be manufactured into high-frequency and ultra-high frequency resistors.
③ Low inherent noise electromotive force, below 10μV/V. ④ Wide resistance range, generally 2.1Ω-10MΩ.
⑤ Power ratings include 1/8W, 1/4W, 1/2W, 1W, 2W, 5W, and 10W.
⑤ High precision: Resistance can be adjusted by cutting butterfly patterns into the film, creating precision resistors.
⑦ Stable pulse load and good pulse adaptability.
③ Easy to manufacture, low production cost, and inexpensive, but relatively large.
⑨ Wide range of applications: Suitable for AC, DC, and pulse circuits.

2 Structure and Characteristics of Metal Film Resistors
Metal film resistors are a type of film resistor. They are formed by coating a ceramic skeleton with a metal film using vacuum evaporation or infiltration. The metal film is typically an anchor alloy, but other metals or alloys can also be used. The outer surface of the resistor is coated with a blue or red protective lacquer. Metal film resistors have the following characteristics:
① Excellent heat resistance, with a rated operating temperature of 70°C and a maximum operating temperature of 155°C.
② Good voltage stability and a low temperature coefficient.
③ Wide operating frequency range and low noise electromotive force, allowing for use in high-frequency circuits.
④ Under the same power conditions, they are significantly smaller than carbon film resistors, approximately half the size of carbon film resistors.
⑤ Precision resistance adjustment can be achieved through butterfly cutting and embossing, with accuracies reaching ±0.5% and ±0.05%.
⑤ Wide resistance range, with resistors available from 1Ω to 1000MΩ.
⑦ Rated power ratings include 0.125W, 0.25W, 0.5W, 1W, 2W, 10W, and 25W.
③ Pulse load stability is poor, inferior to carbon film resistors.
⑨ Widely applicable, suitable for AC, DC, and pulse circuits.

3. Structure and Characteristics of Metal Oxide Film Resistors
Metal oxide film resistors are also a type of film resistor. They are formed by spraying a solution of metal salts such as tin and antimony (such as tin tetrachloride and antimony trichloride salts) onto the surface of a heated ceramic frame, where they are hydrolyzed and deposited. The conductive film of metal oxide film resistors is uniform and firmly bonded to the ceramic frame, resulting in some performance advantages over metal film resistors.

Ordinary metal oxide film resistors have a similar appearance to metal film resistors. They are generally cap-shaped, have axial wires, and are coated with insulating varnish. Specification markings are available in either direct-reading letters or color-coded rings.

Metal oxide film resistors have the following characteristics:
① Compared to metal film resistors, metal oxide film resistors have better oxidation resistance and thermal stability.
② They have excellent pulse and high-frequency overload resistance, as well as good mechanical properties.
③ Due to the thicker conductive film layer, the resistance range is smaller, ranging from 1Ω to 200kΩ. They are primarily used to supplement the low-value resistance of metal film resistors. ④ The temperature coefficient is larger than that of metal film resistors.
⑤ The rated power range is wide, from 1/8W to 50kW.

4 Structure and Characteristics of Synthetic Film Resistors
Synthetic film resistors use carbon black as the conductive material and an organic resin as a binder to form a conductive suspension. This is evenly coated on a ceramic insulating base and then polymerized by heating to produce high-voltage and high-resistance resistors. Some resistors are also encapsulated in a glass shell to form vacuum megohm resistors. Synthetic film resistors are primarily used in instruments such as microcurrent testers, visual humidity meters, high-resistance resistance boxes, and negative ion generators.

Synthetic film resistors have the following characteristics:
① Wide resistance range, up to 1 x 106 MΩ.
② Simple production process and low price.
③ Disadvantages include poor moisture resistance, poor voltage stability, poor frequency characteristics, and high noise.

5 Structure and Characteristics of Glass Glaze Resistors
Glass glaze resistors are also known as glass glaze film resistors, metal ceramic resistors, or thick film resistors. It is made by mixing powdered oxides of precious metals such as silver, palladium, rhodium, and ruthenium (such as palladium oxide and ruthenium oxide) with glass glaze powder. This mixture is then mixed with an organic binder in a specific ratio to form a slurry of a certain viscosity. The slurry is then screen-printed onto a ceramic silicon substrate and sintered at high temperature.

Glass glaze resistors have the following characteristics:
① Moisture and temperature resistance, with good stability.
② Wide resistance range, from 4.7Ω to 200MΩ.
③ Power ratings are generally 1/8W, 1/4W, 1/2W, 1W, and 2W, with high-power models offering 500W.
④ Low noise and excellent high-frequency characteristics.
⑤ Compact size and light weight.

6 Structure and Characteristics of Wirewound Resistors
Wirewound resistors are made of constantan, manganese copper, or nickel-chromium alloy wire wound around a ceramic bobbin. The surface of this type of resistor is often coated with protective paint or glass glaze. Some resistors are enclosed in an insulating casing and filled with heat-resistant filler. Wirewound resistors are divided into fixed resistors and adjustable resistors. Adjustable resistors have exposed wire at the adjustable part, which is not conducive to resistance stability.

Wirewound resistors have the following characteristics:
① Because wirewound resistors are made of high-resistance wire wound on a ceramic bobbin, they offer high-temperature resistance, excellent thermal stability, and a low temperature coefficient, with an operating temperature of up to 300°C.
② Because the material used has a uniform and fine crystal structure, current noise is very low.
③ High power, capable of withstanding high-power loads.
④ Wide resistance range, generally from 0.1Ω to 5MΩ.
⑤ High-precision resistors can be manufactured, with an accuracy of up to ±0.01%.
⑥ Large distribution parameters and poor high-frequency characteristics.
Due to the above characteristics, wirewound resistors can be manufactured into low-noise, heat-resistant, and power-type standard wirewound resistors, precision wirewound resistors, and high-precision wirewound resistors.

7. Functions and Characteristics of Cement Resistors
Resistor wire is wound around an alkaline-free, heat-resistant ceramic element, then protected and secured with heat-, moisture-, and corrosion-resistant materials. Cement resistors consist of a wirewound resistor element enclosed in a square ceramic frame and sealed with a special non-flammable, heat-resistant cement. Their symbol is the same as that of ordinary resistors. Cement resistors offer high resistance and low resistance values.

Characteristics
Compact size, shock and moisture resistance, good heat dissipation, and low price.

Fully insulated, suitable for printed circuit boards.
Wire is wound onto a ceramic rod and then spot-welded to produce precise resistance values.
For high resistance values, metal oxide film is used instead of wire winding.

Excellent heat resistance, low temperature coefficient of resistance, and linear resistance change.

Resistance to short-term overloads; low noise, and high resistance values.

Application: current limiting, shunt, protection, etc.