ECE201 Lect-281 Capacitors (5.1); Inductors (5.2); Dr. S. M. Goodnick November 7, 2003

ECE201 Lect-282 Energy Storage Elements Capacitors store energy in an electric field. Inductors store energy in a magnetic field. Capacitors and inductors are passive elements: –Can store energy supplied by circuit –Can return stored energy to circuit –Cannot supply more energy to circuit than is stored.

ECE201 Lect-283 Power Generation and Distribution Energy storage elements model electrical loads: –Capacitors model computers and other electronics (power supplies). –Inductors model motors.

ECE201 Lect-284 Signal Processing Communication Instrumentation Capacitors and inductors are used to build filters and amplifiers with desired frequency responses: –Instrumentation amplifiers. Capacitors are used in analog-to-digital (A/D) converters to hold a sampled signal until it can be converted into bits.

ECE201 Lect-285 Solid State Digital Design Integrated circuits (ICs) have layers of conductors (metal, silicon with impurities) with insulators (glass) between. This is a capacitor! This capacitance is one of the limiting factors in processor speeds. This capacitance is used to create RAMs.

ECE201 Lect-286 Electromagnetics For high frequency signals, inductance and capacitance are more significant effects than resistance.

ECE201 Lect-287 Capacitance Capacitance occurs when two conductors (plates) are separated by a dielectric (insulator). Charge on the two conductors creates an electric field that stores energy

ECE201 Lect-288 CAPACITORS First of the energy storage devices to be discussed Typical Capacitors Basic parallel-plates capacitor CIRCUIT REPRESENTATION NOTICE USE OF PASSIVE SIGN CONVENTION

ECE201 Lect-289 Capacitance The voltage difference between the two conductors is proportional to the charge: q = C v The proportionality constant C is called capacitance. Units of Farads (F) – Coulomb/Volt

ECE201 Lect-2810 Capacitor i(t) + – v(t) The rest of the circuit

ECE201 Lect-2811 Capacitor Voltage

ECE201 Lect-2812 Energy Stored

ECE201 Lect-2813 Class Examples Learning Extension E5.2 Learning Extension E5.3

ECE201 Lect-2814

ECE201 Lect-2815 Inductance Inductance occurs when current flows through a (real) conductor. The current flowing through the conductor sets up a magnetic field that is proportional to the current. The voltage difference across the conductor is proportional to the rate of change of the magnetic field.

ECE201 Lect-2816 Inductance The voltage difference across the inductor is proportional to the rate of change of the current. The proportionality constant is called the inductance, denoted L Units of Henrys (H) - V·s/A

ECE201 Lect-2817 Flux lines may extend beyond inductor creating stray inductance effects Circuit representation for an inductor A TIME VARYING FLUX CREATES A COUNTER EMF AND CAUSES A VOLTAGE TO APPEAR AT THE TERMINALS OF THE DEVICE INDUCTORS NOTICE USE OF PASSIVE SIGN CONVENTION

ECE201 Lect-2818 Cell Phone: Much of Area Consumed by discrete Inductors and Capacitors of Filters

ECE201 Lect-2819 Inductor i(t) + – v(t) The rest of the circuit H

ECE201 Lect-2820 Inductor Current

ECE201 Lect-2821 Energy Stored

ECE201 Lect-2822 Class Examples Learning Extension E5.4 Learning Extension E5.5