Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

Chapter 6Chapter 6

Capacitors and InductorsCapacitors and Inductors

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

CapacitorsCapacitors

A typical capacitor

A capacitor consists of two conducting plates separated by an insulator (or dielectric).

C: capacitance

Unit: farad(F)

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

Values: picofarad (pF) -- microfarad (mF)

Polyester

Mica

Electrolytic

Ceramic

Types: fixed

variable

Circuit symbols for capacitors a) fixed capacitor b) variable capacitor

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

VAR of CapacitorVAR of 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)

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

Stored Energy in Capacitor

Is capacitor active?

equivalent circuit for the parallel capacitors

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

Equivalent circuit for the series capacitors

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

InductorsInductors

An inductor consists of a coil of conducting wire.

Typical form of an inductorL: inductance

Unit: henry (H)

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

Circuit symbols for inductors

Values: microhenrys(H)--- tens of henrys(H)

Types: Fixed

variable

Iron, steel

Plastic, air

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

VAR of InductorVAR of Inductor

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).

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

Stored Energy in Inductor

Is inductor active?

Equivalent circuit for the series inductors

Neq LLLLL ...321

Basic Theory of Circuits, SJTUBasic Theory of Circuits, SJTU

Equivalent circuit for the parallel inductors