Mica capacitors

Chapter Mica capacitors

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

  • These capacitors can still sometimes be found in electronic equipment. They havevalues ranging from about 0.001 µF to 0.1 µF, and can handle low to moderate voltages,usually up to about 1000 V.Mica capacitorsWhen you were a child, you might have seen mica, a naturally occurring, transparentsubstance that flakes off in thin sheets. This material makes an excellent dielectric forcapacitors.Mica capacitors can be made by alternately stacking metal sheets and layers ofmica, or by applying silver ink to the sheets of mica. The metal sheets are wired together into two meshed sets, forming the two terminals of the capacitor. This schemeis shown in Fig. 11-6.Ceramic capacitors20511-6Meshing of plates to increase capacitance.Mica capacitors have low loss; that is, they waste very little power as heat, providedtheir voltage rating is not exceeded. Voltage ratings can be up to several thousand voltsif thick sheets of mica are used. But mica capacitors tend to be large physically in pro-portion to their capacitance. The main application for mica capacitors is in radio re-ceivers and transmitters. Their capacitances are a little lower than those of papercapacitors, ranging from a few tens of picofarads up to about 0.05 µF.Ceramic capacitorsPorcelain is another material that works well as a dielectric. Sheets of metal are stackedalternately with wafers of ceramic to make these capacitors. The meshing/layeringgeometry of Fig. 11-6 is used. Ceramic, like mica, has quite low loss, and therefore al-lows for high efficiency.