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| Resistors are ubiquitous. As a result of this their efficiency is taken for granted, offered they are operated inside their power, voltage and environmental ratings this is sensible, given that following millions of accumulated resistor-years expertise there is certainly tiny left for their producers to discover. But you'll find nonetheless applications exactly where specifying and applying resistors requires to become handled with some care. Resistor types - Surface mount chip The most prevalent common objective resistor could be the thick film surface mount chip sort. Accessible in large quantities and incredibly low costs, it truly is the workhorse from the resistor world. The construction is very simple and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations features a resistive ink film printed or otherwise deposited on its leading surface. The terminations are coated having a solder dip to make sure ease of wetting when the element is soldered into place, and the best with the part is IBM Certified Sales Specialist coated with an epoxy or glass layer to safeguard the resistive element. Diverse manufacturers make a variety of claims for the ruggedness and efficiency of their parts but the fundamental options are related. Energy dissipation is largely controlled by the thermal properties from the PCB pads to which the chip is soldered, and in case you are operating close for the rated energy from the component it's going to be essential to confirm that your pad style agrees together with the manufacturer's recommendations. You can also get metal film chip resistors for greater overall performance applications, but these are additional highly-priced than the popular thick film. The resistive ink strategy utilized for chips can also create regular axial-lead resistors (metal glaze) of tiny size, and can be employed directly onto a substrate to generate printed resistors. This method is frequently applied in hybrid circuits and is incredibly cost-effective especially when large numbers of similar values are necessary. It really is doable to print resistors straight onto fibreglass printed circuit board, though the result is of pretty poor quality and can not be made use of where a stable, predictable worth (compared with conventional forms) is expected. Metal film The subsequent most popular type is the metal film, in its numerous guises. This can be the regular component for industrial and military purposes. By far the most well known varieties of leaded metal film are hardly any far more expensive than carbon film and, provided their superior characteristics, particularly temperature coefficient, noise and power handling ability, lots of equipment producers do not find it worthwhile to bother with carbon film. Variants from the regular metal film cater for high or low resistance demands. The "metal" within a metal film is usually a nickel-chromium alloy of varying composition for diverse resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the end caps and leads are force-fitted for the tubular assembly as well as the resistance element IBM Certified Integration Developer is trimmed to worth by cutting a helical groove of controlled dimensions in it, which makes it possible for the identical film composition to become used more than rather a wide range of nominal values. The whole element is then coated in epoxy and marked. The disadvantage with the helical trimming approach is the fact that it inherently increases the resistor's stray inductance, as well as limits its pulse handling capability. Carbon The most typical leaded resistor for commercial applications is definitely the carbon film. It is actually absolutely affordable - much less than a penny in quantity. It also has the least impressive efficiency when it comes to tolerance and temperature coefficient, however it is usually adequate for common purpose use. The other sort which uses pure carbon as the resistive element is carbon composition, which was the earliest sort of resistor but nowadays finds a use in particular applications which involve an assured pulse withstand capability. Wirewound For medium and high energy (greater than 2W) applications the wirewound resistor is practically universally utilised. It is pretty cheap and readily accessible. Its disadvantages are its bulk, even though this enables a lower surface temperature to get a given power dissipation; and that due to its construction it's noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound kinds are accessible either using a vitreous enamel or cement coating, or in an aluminium housing which could be mounted to a heatsink. Aluminium housings can give power dissipations exceeding 100W per unit. Precision resistors Once circuit needs get started to call for accuracy and drift specifications exceeding the usual metal film abilities, the cost increases substantially. It is nonetheless possible to get metal film resistors of "precision" performance as much as an order of magnitude much better than the normal, although at rates an order of magnitude or far more larger. Drift specifications of less than 10 parts-per-million per °C introduce quite a few a lot more significant components in to the efficiency equation, like thermal emf, mechanical and thermal anxiety, and terminating resistance. These is usually dealt with, and also the resistive and substrate materials can be optimised, but the unit expenses are now measured in pounds, and delivery occasions stretch to months. Resistor networks Thick film resistor networks are manufactured like chips. A resistive ink is screen printed onto a ceramic substrate to form quite a few resistors at after, which can be then encapsulated to form a multi-resistor single package. The resulting resistors have the same efficiency as a single thick film chip, though with reduced breakdown voltage and energy handling capability. Printed Circuit Passive Components Resistors are ubiquitous. Because of this their efficiency is taken for granted, provided they may be operated within their energy, voltage and environmental ratings this can be sensible, since right after millions of accumulated resistor-years expertise there is little left for their producers to find out. But there are actually nevertheless applications where specifying and applying resistors requires to be handled with some care. Resistor types - Surface mount chip The most typical general objective resistor will be the thick film surface mount chip type. Readily available in large quantities and very low rates, it really is the workhorse on the resistor world. The construction is really very simple and hardly varies from manufacturer to manufacturer. An alumina (aluminium oxide ceramic) substrate with nickel plated terminations has a resistive ink film printed or otherwise deposited on its top surface. The terminations are coated with a solder dip to ensure ease of wetting when the part is soldered into place, and the best from the portion is coated with an epoxy or glass layer to protect the resistive element. Distinctive manufacturers make several claims for the ruggedness and overall performance of their parts but the simple functions are related. Power dissipation is largely controlled by the thermal properties with the PCB pads to which the chip is soldered, and if you're running close towards the rated power on the component it'll be necessary to confirm that your pad design agrees with the manufacturer's recommendations. You can also get metal film chip resistors for higher performance applications, but these are far more high-priced than the common thick film. The resistive ink method utilized for chips can also make normal axial-lead resistors (metal glaze) of little size, and can be applied straight onto a substrate to produce printed resistors. This approach is often applied in hybrid circuits and is incredibly cost-effective especially when huge numbers of similar values are needed. It truly is probable to print resistors directly onto fibreglass printed circuit board, even though the outcome is of incredibly poor top quality and can't be utilized exactly where a stable, predictable value (compared with conventional types) is required. Metal film The subsequent most common kind is the metal film, in its different guises. This can be the regular part for industrial and military purposes. Probably the most well-known varieties of leaded metal film are hardly any a lot more costly than carbon film and, offered their superior characteristics, particularly temperature coefficient, noise and power handling ability, numerous equipment manufacturers usually do not obtain it worthwhile to bother with carbon film. Variants of your common metal film cater for high or low resistance desires. The "metal" inside a metal film is often a nickel-chromium alloy of varying composition for various resistance ranges. A film of this alloy is plated onto an alumina substrate. For leaded parts, the finish caps and leads are force-fitted for the tubular assembly plus the resistance element is trimmed to worth by cutting a helical groove of controlled dimensions in it, which allows the same film composition to be utilized more than fairly a wide range of nominal values. The whole part is then coated in epoxy and marked. The disadvantage of your helical trimming process is the fact that it inherently increases the resistor's stray inductance, and also limits its pulse IBM Certifications handling capability. Carbon The most widespread leaded resistor for commercial applications will be the carbon film. It is actually undoubtedly inexpensive - less than a penny in quantity. It also has the least impressive overall performance in terms of tolerance and temperature coefficient, however it is commonly sufficient for general objective use. The other sort which utilizes pure carbon because the resistive element is carbon composition, which was the earliest sort of resistor but these days finds a use in certain applications which involve an assured pulse withstand capability. Wirewound For medium and high power (higher than 2W) applications the wirewound resistor is just about universally employed. It's pretty cheap and readily obtainable. Its disadvantages are its bulk, although this enables a lower surface temperature to get a given power dissipation; and that because of its construction it is noticeably inductive, which limits its use in high frequency or pulse applications. Wirewound varieties are obtainable either using a vitreous enamel or cement coating, or in an aluminium housing which can be mounted to a heatsink. Aluminium housings can present energy dissipations exceeding 100W per unit. Precision resistors Once circuit specifications start off to call for accuracy and drift specifications exceeding the usual metal film skills, the price increases substantially. It is actually still probable to have metal film resistors of "precision" overall performance as much as an order of magnitude improved than the common, even though at costs an order of magnitude or much more greater. Drift requirements of much less than 10 parts-per-million per °C introduce several more substantial factors into the overall performance equation, for instance thermal emf, mechanical and thermal pressure, and terminating resistance. These may be dealt with, and also the resistive and substrate supplies could be optimised, but the unit expenses are now measured in pounds, and delivery instances stretch to months. Resistor networks Thick film resistor networks are manufactured like chips. A resistive ink is screen printed onto a ceramic substrate to form a lot of resistors at when, that is then encapsulated to form a multi-resistor single package. The resulting resistors have exactly the same performance as a single thick film chip, even though with decreased breakdown voltage and energy handling capability. |
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