Voltage and Current Sources Circuit Symbols ECE 201

Voltage and Current Sources Circuit Symbols ECE 201 Circuit Theory I 1

“IDEAL” or “Independent” Sources • IDEAL voltage source – maintains the prescribed voltage across its terminals regardless of the current drawn from it • IDEAL current source – maintains the prescribed current through its terminals regardless of the voltage across those terminals ECE 201 Circuit Theory I 2

“Controlled” or “Dependent” Sources • A voltage or current source whose value “depends” on the value of voltage or current elsewhere in the circuit • Use a diamond-shaped symbol ECE 201 Circuit Theory I 3

Voltage-Controlled Voltage Source VCVS • Vs is the “output” voltage • Vx is the “reference” voltage • u is the “multiplier” • Vs = u. Vx ECE 201 Circuit Theory I 4

Current-Controlled Voltage Source CCVS • Vs is the “output” voltage • Ix is the “reference” current • p is the multiplier • Vs = p. Ix ECE 201 Circuit Theory I 5

Voltage-Controlled Current Source VCCS • Is is the “output” current • Vx is the “reference” voltage • a is the multiplier • Is = a. Ix ECE 201 Circuit Theory I 6

Current-Controlled Current Source CCCS • Is is the “output” current • Ix is the “reference” current • b is the multiplier • Is = b. Ix ECE 201 Circuit Theory I 7

Common-Emitter Transistor Amplifier ECE 201 Circuit Theory I 8

The transistor and its equivalent circuit ECE 201 Circuit Theory I 9

Substituting the equivalent circuit for Q 1 ECE 201 Circuit Theory I 10

Active and Passive Elements • Active element • Passive element – a device capable of generating electrical energy – a device that absorbs electrical energy • Voltage source • Current source • Power source – Batteries – Generators – a device that needs to be powered (biased) • • • Resistor Capacitor Inductor motor light bulb heating element • transistor ECE 201 Circuit Theory I 11