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Related knowledge of chip resistors
2019-11-27
 
I. Overview
Chip fixed resistor, directly translated from Chip Fixed Resistor, commonly known as chip resistor (SMD Resistor), is a kind of metallic glass uranium resistor. It is a resistor made by mixing metal powder and glass uranium powder and using a screen printing method to print a high-power chip resistor on a substrate. Resistant to humidity, high temperature, and small temperature coefficient. Can greatly save circuit space costs and make the design more refined. The application of surface mount technology (SMT) has become very common, and the proportion of electronic products assembled using SMT has exceeded 90%. Since the 1980s, China has started to use SMT technology. With the development of small SMT production equipment, the application range of SMT is further expanding. Aviation, aerospace, instrumentation, machine tools and other fields are also using SMT to produce various small-volume electronic products or components.

Second, characteristics
Small size and light weight;
Adapt to reflow and wave soldering;
· Stable electrical performance and high reliability;
· Low assembly cost and match with automatic placement equipment;
· High mechanical strength and excellent high frequency characteristics.

Third, the identification method
Digital Nominal Nominal
(Generally rectangular chip resistors use this nominal method)
The digital cable nominal method is to use three digits on the resistor body to indicate its resistance value. Its first and second digits are significant digits, and the third digit indicates the number of "0" added after the significant digits. No letters appear in this digit.
For example: "472 '" means "4700Ω"; "151" means "150Ω". If it is a decimal number, use "R" to indicate "decimal point" and occupy one significant digit, and the remaining two digits are significant digits.
For example: "2R4" means "2.4Ω"; "R15" means "0. 15Ω".

Fourth, the color ring nominal method
(Generally cylindrical fixed resistors use this nominal method)
The chip resistance is the same as the general resistance, and most of them use four rings (sometimes three rings) to indicate the resistance value. The first and second rings are significant figures, and the third ring is the magnification. For example: "Brown Green Black" means "15Ω"; "Blue Gray Orange Silver" means "68kΩ" error ± 10%.

Five, E96 number code and letter mixed nominal method
The numerical code and letter mixed nominal method also uses three digits to indicate the resistance value, that is, "two digits plus one letter", where the two digits represent the E96 series resistance code. The third digit is the magnification in letter code. For example: “51D” means “332 × 103; 332kΩ”; “249Y” means “249 × 10-2; 2.49Ω”.

Six, the cause of damage
1. The chip resistor is too close to the power transformer, and the line impedance at both ends is very small. The inverter does not have a DC reactor and an AC reactor on the output side, so that the rectifier bridge is under the impact of high amplitude sharp pulse current of capacitive filtering. Causes premature damage to the rectifier bridge.
2. I didn't buy the original device, and the quality is not good.
3. The back-end circuit and inverter power switching device are damaged, which causes the rectifier bridge to flow through the short-circuit current and be damaged.
4. The output current voltage is too low, which reduces the burden on the rectifier bridge and damages it.
5. The voltage of the power grid becomes instantaneously high, and the lightning or surge voltage is too high, and the internal resistance of the power grid is small. The protection of the power grid resistance will not work after breakdown and burnout, resulting in all overvoltages being added to the rectifier bridge.

Seven solutions
1. When replacing the new rectifier bridge and chip resistor device, ensure that the rectifier bridge is welded firmly and maintain a safe distance from the surrounding devices. In addition, apply silicone grease to reduce the resistance heat.
 2. For parallel rectifier bridges, the products of the same model and the same manufacturer shall be used to prevent damage caused by uneven current.

Eight, and the difference between alloy resistance
Chip resistors are a large category, meaning packages are in the form of surface-mount packages.
Alloy resistance is a type of resistance using alloy as the current medium. It generally has the characteristics of low resistance, high precision, low temperature coefficient, inrush current resistance, high power and so on. This type of resistor is common in various electronic products, and is mainly used in current sampling or short circuit protection.
The mainstream alloy resistance is chip alloy resistance. The main material of the alloy is copper, plus other materials, it becomes constantan, manganese copper, etc. There are many other auxiliary materials, but the main performance is determined by the alloy material itself.
The chip resistors often mentioned in our daily life generally refer to ordinary types of chip thick film and thin film resistors.
The two concepts are classified at different levels.
Compared to thin films, thick films are classified from the perspective of materials and processes;
A resistor may be both a thick film and a patch, that is, a thick film printing process is used to make a chip resistor.
Of course, thick film printing can also be used for thick film hybrid circuits, and chip resistors can also be made using thin film processes.
In terms of price: The price of alloy resistors is generally much more expensive than that of chip thick film resistors, about 0.1-0.2 yuan. Of course, the larger the package, the more precise the precision, and the more expensive it is. The price of thick film resistors ranges from a few dollars / kpcs to tens of dollars / kpcs, which is also differentiated according to packaging and accuracy.
The precision of alloy resistors is much more precise than that of thick film resistors. Thick film resistors are generally 1% and 5%, while alloy resistors can reach less than 1%.
 
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