EECE 281 Lecture 5 2010

EECE 281 Lecture 5 2010 - EECE 281 Seminar 1 Professor...

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rofessor Charles Westgate EECE 281 Seminar 1 Professor Charles Westgate Capacitors and Ultracapacitors

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Objectives c To understand the role of capacitors in digital circuits and their important effects on energy dissipation c To discuss how capacitors are constructed and how to determine the value of capacitors introduce percapacitors tracapacitors d their c To introduce supercapacitors or ultracapacitors and their potential applications
Basic capacitor characteristics c Capacitors can store charge c When a voltage is applied across a capacitor, a charge is stored he stored charge can be depicted as shown: farads in e capacitanc the is and applied, voltage the is coulombs, in charge the is where C V Q CV Q = c The stored charge can be depicted as shown:

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Energy stored on a capacitor c When a capacitor is charged to a voltage V, the energy stored is: his energy is provided by a voltage source such as a power 2 2 1 CV E = c This energy is provided by a voltage source such as a power supply or a battery. c When a capacitor is charged to a voltage V, there is an equal amount of energy dissipated in resistances of wires connecting the battery to the capacitor, the voltage source, etc. in the circuit.
Role of capacitors in digital circuits c Capacitances appear in every circuit either as discrete elements placed in the circuit by the designed to obtain desired performance or as stray or parasitic capacitances that are not intentional but are always present. ny two wires or conductors separated by an insulator c Any two wires or conductors separated by an insulator corresponds to a capacitance. c In digital circuits, stray capacitances appear in interconnects (the conductors connecting one digital circuit to another or in the transistors that make up digital circuits.

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Consider the simple inverter An external power supply of 3 to 5 volts is connected to Vdd. In a CMOS inverter, two transistors are
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This note was uploaded on 11/07/2010 for the course ECH 434 taught by Professor Dfs during the Spring '10 term at Binghamton.

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EECE 281 Lecture 5 2010 - EECE 281 Seminar 1 Professor...

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