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Voltage and Current Sources Circuit Symbols. 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. - PowerPoint PPT Presentation
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ECE 201 Circuit Theory I 1
Voltage and Current Sources
Circuit Symbols
Vbattery12 V
Isource1 A
ECE 201 Circuit Theory I 2
“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
Vs12 V
LOAD
Z=A
+jB
LOADCurrent
DC 1e-009Ohm
0.012 A+ -
LOAD
Z=A
+jB
Is1 A
LOADVoltageDC 1MOhm 999.001 V
+
-
ECE 201 Circuit Theory I 3
“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
Vs1 V/V Vs=uVxVx
+
-
+
-
ECE 201 Circuit Theory I 4
Voltage-Controlled Voltage Source VCVS
• Vs is the “output” voltage
• Vx is the “reference” voltage
• u is the “multiplier”
• Vs = uVx
Vs1 V/V Vs=uVxVx
+
-
+
-
ECE 201 Circuit Theory I 5
Current-Controlled Voltage Source CCVS
• Vs is the “output” voltage
• Ix is the “reference” current
• p is the multiplier
• Vs = pIx
Vs1 Ohm Vs=pIx
-
+
Ix
ECE 201 Circuit Theory I 6
Voltage-Controlled Current Source VCCS
• Is is the “output” current
• Vx is the “reference” voltage
• a is the multiplier
• Is = aIx
Is1 Mho Vx
+
-
Is = aVx
ECE 201 Circuit Theory I 7
Current-Controlled Current Source CCCS
• Is is the “output” current
• Ix is the “reference” current
• b is the multiplier
• Is = bIx
Is1 A/A Ix Is=bIx
ECE 201 Circuit Theory I 8
Common-Emitter Transistor Amplifier
Q1
2N2222A
R11kOhm
R247kOhm
Rcollector3.3kOhm
Remitter560 Ohm
VCC
12V
BASE
COLLECTOR
EMITTER
Cc1
1uF
Cc2
1uF
Rload1kOhm
V1
1 V 1kHz 0Deg Ce
1uF
ECE 201 Circuit Theory I 9
The transistor and its equivalent circuit
Q
2N2222ABASE
COLLECTOR
EMITTER
I11 A/A
rbe
1kOhm COLLECTOR
EMITTER
BASE
ECE 201 Circuit Theory I 10
Substituting the equivalent circuit for Q1
R11kOhm
R247kOhm Rcollector
3.3kOhm
Remitter560 Ohm
VCC
12V
BASECOLLECTOR
EMITTER
Cc1
1uF
Cc2
1uF
Rload1kOhm
V1
1 V 1kHz 0Deg Ce
1uF
BETAib50 A/A
rbe
1kOhm
ib --->
ECE 201 Circuit Theory I 11
Active and Passive Elements
• Active element– a device capable of
generating electrical energy
• Voltage source• Current source• Power source
– Batteries– Generators
– a device that needs to be powered (biased)
• transistor
• Passive element– a device that absorbs
electrical energy• Resistor• Capacitor• Inductor• motor• light bulb• heating element