1, resistance (patch, for example)
1.1 selection according to the
(1) resistance: resistance; M. R K
(2) packaging: commonly used packaging 0201040 2060 3080 5120 6181 2182,
(3) power consumption: 1/16 w, w 1/10, 1/8 w, a quarter w, 1/2 w, 1 w, 2 w, 3 w, etc.,
(4) accuracy: 1%, 5%, etc.,
1.2 selection method
(1) priority value, for uncommon resistance, can be equivalent to replace through resistance of series and parallel,
(2) power consumption: P=I2R U2/R or UI, according to the power consumption, reasonable choose encapsulation, 1/16 general maximum power consumption of the 0402 w, 0603 the maximum power consumption for 1/10 w, 0805 the maximum power consumption for 1/8 w, specific components of the data sheet,
(3) considering accuracy: as a feedback loop, pressure resistance, generally choose the accuracy of 1%; Other, choose the accuracy of 5%,
(4) considering cost: precision is 1% more expensive than 5% accuracy; Packaging is different, the price also some difference, the commonly used packaging, the price a little cheaper,
(5) consider PCB size: the smaller boards, packaging as far as possible with a small point, such as miniature multi-purpose products 0402; General products, 0603,
(6) consider processing: the greater the size, the lower the requirements for processing technology, general plant can produce 0603 and 0402,
(7) consider maintenance: the smaller the size, the larger the welding difficulty,
2, the capacitance
2.1 selection according to the
(1) the capacity value: capacitance value; PF, nF, uF,
(2) the capacitance types: ceramic capacitors, aluminum electrolytic capacitors, tantalum capacitors, etc.
(3) the parasitic parameters: ESR, affect the filtering effect,
(4) size: plug-in package, SMD encapsulation.
(5) price: affect the product cost,
(6) size: impact structure,
(7) : precision ceramic capacitors are greatly influenced by temperature, electrolytic capacitor change,
2, the selection method
(1) priority value, capacitance is energy storage device, the capacitance value, the greater the moment can provide more energy, load current, the greater the capacitance value choice, the greater the smaller if the capacitance value, cannot provide enough current moment, voltage will be drop down, the ripple, affect other circuits, in addition, as a result of the existence of parasitic parameters, frequency response, the greater the capacitance is not better, best, right such as integrated circuit within the main switch circuit, high frequency, generally choose 0.1 uF,
(2) the capacity value is determined, choose the type of capacitance, generally less than 10 uF, choice ceramic capacitors, more than 10 uF, less than a few hundred uF, can choose the aluminum electrolysis and tantalum electrolytic capacitor, more than hundreds of uF, generally choose the aluminum electrolytic capacitor, wave record (3.3 V/5 V circuit optional 104/105).
(3) choose packaging, packaging options to consider pressure, age, structure, process, cost, etc., such as aluminum electrolytic capacitor, a plug-in is cheaper, good processing patch,
(4) pressure, better ceramic capacitance pressure, tantalum electrolytic capacitor voltage is poorer, pressure value is greater than the best of tantalum electrolytic capacitor circuit voltage of 2 times the left and right sides,
(5) the life aspects, aluminum electrolytic capacitor is poorer, the electrodes are greatly influenced by temperature, the design, keep away from heat source,
(6) other aspects, tantalum electrolytic capacitor price is higher, but the packaging is small, filtering effect is good. Aluminum electrolytic capacitor cheap, filtering effect is a bit poor, generally with ceramic capacitors in parallel, minimize the ESR, improve filtering effect,
3, the inductance
3.1 selection according to the
(1) value: the feeling of inductance values; UH, H,
(2) the inductance type: power inductors, inductance, common-mode inductor, such as
(3) the inductance parameters; DCR, saturation current, current, temperature
(4) size: plug-in package, SMT packaging (common),
(5) size: impact structure,
3.2 selection method
(1) preference inductance type: signal filtering, generally choose 0603040 2 commonly used SMT packaging; Power circuit, generally choose power inductors, inductance power block type of EMC is better, but the price is a bit expensive,
(2) choose inductance, filter, calculate according to the signal frequency; Power inductor, generally according to the power supply IC can be recommended by the manual, impact ripple, load and dynamic response,
(3) according to the DCR, saturation current, the current temperature to choose the appropriate size, in general, the size, the greater the parameters, the better, but the price is more expensive, at the same time, the structure will be restricted,
(4) DCR as small as possible, according to the I2R power, the greater the DCR, fever, the greater the power conversion efficiency is lower,
(5) the saturation current must be greater than the maximum current of inductor, if the inductor saturation, sense of value will decrease sharply, lose the role of energy storage, the equivalent of a wire, damage circuit,
(6) the greater the current temperature, the better, the smaller the fever,
4, summary
Resistor, capacitor, inductor is indispensable passive components in the circuit, the application need reasonable choice, satisfy the function of the circuit, and meet the requirements of product quality, reasonable and effective choice RLC, helps to improve product performance,
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