Film type resistors

Chapter Film type resistors

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • One of the advantages of wirewound resistors is that they can be made to have val-ues within a very close range; that is, they are precision components. Another advan-tage is that wirewound resistors can be made to handle large amounts of power. Somewirewounds might actually do well as electric heaters, dissipating hundreds, or eventhousands of watts.A disadvantage of wirewound resistors, in some applications, is that they act like in-ductors. This makes them unsuitable for use in most radio-frequency circuits.Wirewound resistors usually have low to moderate values of resistance.Film type resistorsCarbon, nichrome, or some mixture of ceramic and metal (cermet) can be applied to acylindrical form as a film, or thin layer, in order to obtain a desired value of resistance.This type of resistor is called a carbon-film resistor or metal-film resistor. It looks likea carbon-composition type, but the construction technique is different (Fig. 6-7).104 Resistors6-7Construction of a film type resistor.The cylindrical form is made of an insulating substance, such as porcelain. The filmis deposited on this form by various methods, and the value tailored as desired.Metal-film units can be made to have nearly exact values. Film type resistors usuallyhave low to medium-high resistance.A major advantage of film type resistors is that they, like carbon-composition units,do not have much inductance or capacitance. A disadvantage, in some applications, isthat they can’t handle as much power as the more massive carbon-composition units oras wirewound types.Integrated- circuit resistorsIncreasingly, whole electronic circuits are being fabricated on semiconductor wafersknown as integrated circuits (ICs).It is possible nowadays to put a whole radio receiver