Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: THEend8_
Foundations of Electronics I
Lecture 4 (Week 5)
Parallel resistive circuits
Kirchhoff’s current law
Power in parallel circuits
Francisco Sepulveda
CE163
Parallel
Circuits
Required reading:
Resistors in Parallel
Example Show how to connect the resistors on the
breadboard in parallel.
Resistors in Parallel
Solution: This is one way. Notice that one node is colored in pink;
the other is black and all resistors are between these two
nodes.
A parallel circuit is identified by the fact that it has more
than one current path (branch) connected to a common
voltage source.
Parallel Circuit Rule for Voltage
Because all components are connected across the same
voltage source, the voltage across each is the same.
For example, the source voltage is +5.0 V. What will a
voltmeter read if it is placed across each of the resistors?
Parallel vs. Series circuits
Series network:
same current at all components
different voltages at each component
use KVL and voltage divider
Parallel network:
same voltages at all branches
different currents at each branch
use KCL and current divider
Parallel Resistors
The total resistance of resistors in parallel is the reciprocal
of the sum of the sum of the reciprocals of the individual
resistors:
Example:
The resistors in a certain parallel circuit are 680Ω, 1.5kΩ, and
2.2kΩ. What is the total resistance? 386 W
NB: in parallel circuits, the total (or equivalent) resistance is always smaller
than any of the individual resistances.
Two Parallel Resistors
The special case of resistance
of two parallel resistors can be
found by:
R =
1
1
R
+
1
R
which can be
reduced to
R =
RR
R + R
This is called the
product-over-sum
rule.
Example: Calculate the total resistance if R = 27kΩ and
R = 56kΩ.
= 18.2kΩR =
27Ω x 56Ω
27Ω + 56Ω
Parallel Circuits
Tabulating current, resistance, voltage, and power is a useful way to
summarize parameters in a parallel circuit.