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Circuits and Devices
Schematic Diagrams and Symbols
Peter Mathys
ECEN 1400
• A circuit is a collection of interconnected
electrical devices such that charge (usually
electrons) can flow through it continuously
without beginning or end.
• Each electrical device is a component that is
treated as a separate entity.
• Devices typically encountered in circuits are
batteries, resistors, capacitors, inductors, diodes,
transistors, OpAmps, integrated circuits, etc.
Circuit Symbols
Example
• To specify and document electrical circuits,
standardized symbols are used for the devices
and the wires that interconnect them.
• Circuit symbols are also used for conceptual
devices such as ideal voltage and current
sources, and to simplify schematics, e.g., by
using a common reference or ground potential
with an associated ground symbol.
(Ideal) Sources and Ground
Physical Circuit
Corresponding
Schematic Diagram
Example Using Ground
In electronic circuits
ground is used as an
electrical reference point.
Simple flashlight circuit with voltage source, switch, and lamp.
In electrical power
distribution systems ground
(“earth”) is the electrical
potential of the Earth’s
conductive surface.
(a) All wires shown
explicitly
(b) Bottom wire
replaced by
connection
through ground.
(c) Using ground
connections and
battery as source.
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Switches
Resistors
SPDT switch, construction view
Standard Values
Color Code
Standard values for resistors and other components. The most common values
are shown in bold on the first line.
Lamps and LEDs
Diodes
Diodes are “oneway streets” for
current.
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Capacitors
Inductors, Transformers
Transistors (BJT)
Transistors (JFET, MOSFET)
BJT: Bipolar Junction Transistor
JFET: Junction Field-Effect Transistor
MOSFET: Metal Oxide Semiconductor
Field-Effect Transistor
Operational Amplifiers
Example
Switching Regulator:
Simple but nontrivial example of a
schematic.
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