上海交大模电讲稿06.ppt

Basic Theory of Circuits, SJTU Chapter 6 Capacitors and Inductors Capacitors VAR of Capacitor Inductors VAR of Inductor * * A typical capacitor A capacitor consists of two conducting plates separated by an insulator (or dielectric). C: capacitance Unit: farad(F) Values: picofarad (pF) -- microfarad (mF) Polyester Mica Electrolytic Ceramic Types: fixed variable Circuit symbols for capacitors a) fixed capacitor b) variable capacitor Passive sign convention A capacitor is an open circuit to dc The voltage on the capacitor cannot change abruptly (in condition that i is limited) Stored Energy in Capacitor Is capacitor active? equivalent circuit for the parallel capacitors Equivalent circuit for the series capacitors An inductor consists of a coil of conducting wire. Typical form of an inductor L: inductance Unit: henry (H) Circuit symbols for inductors Values: microhenrys(?H)--- tens of henrys(H) Types: Fixed variable Iron, steel Plastic, air What happens when the current is constant? Integrating form: An inductor acts like a short circuit to dc. The current through an inductor cannot change abruptly (in condition that v is limited). Stored Energy in Inductor Is inductor active? Equivalent circuit for the series inductors Equivalent circuit for the parallel inductors