EE301 – Lesson 29 Reading: 22.4 1 2 2 2 sec P S S LD P refl S P S LD a a a a a = = = = = E E E V Z I I I I Ζ Transformers and Reflected Impedance Learning Objectives (a) Predict the reflected impedance and derive an equivalent circuit using the reflected impedance. (b) Calculate the transformation ratio to deliver maximum power to a load. (c) Determine safe operation parameters from power transformer ratings. (d) Explain how the transformer acts as an isolation device. (e) List and explain several practical applications of transformers. Reflected Impedance Transformers make load impedances “look” bigger or smaller depending on their turns ratio. Z P refl is the impedance that “appears” at the primary windings. In the circuit shown above on the left, what impedance does the primary-side source “see” due to the impedance on the secondary side? The term a 2 Z sec is referred to as the load’s reflected impedance. Power Supply Transformers Power supply transformers are used to convert incoming 120 Vac to voltages of various levels necessary for different circuits. Transformers for Power Systems Impedance Matching Transformers are used to raise or lower the apparent impedance in order to achieve maximum power transfer.
(a) Predict the reflected impedance and derive an equivalent
circuit using the reflected impedance. (b) Calculate the
transformation ratio to deliver maximum power to a load. (c)
Determine safe operation parameters from power transformer ratings.
(d) Explain how the transformer acts as an isolation device. (e)
List and explain several practical applications of
transformers.
Reflected Impedance Transformers make load impedances look
bigger or smaller depending on their turns ratio. ZP refl is the
impedance that appears at the primary windings. In the circuit
shown above on the left, what impedance does the primary-side
source see due to the impedance on the secondary side? The term
a2Zsec is referred to as the loads reflected impedance.
Power Supply Transformers Power supply transformers are used to
convert incoming 120 Vac to voltages of various levels necessary
for different circuits.
Transformers for Power Systems Impedance Matching Transformers
are used to raise or lower the apparent impedance in order to
achieve maximum power transfer.
EE301 Lesson 29 Reading: 22.4
2
Example 1 For the circuit shown below, use the reflected
impedance concept to solve for the total impedance ZT. Determine Ig
and ILD. Solution:
Example 2 An amplifier is modeled with a Thvenin equivalent
impedance of 36-54j . (a) What load impedance must be chosen to
ensure maximum power transfer occurs? (b) What is the transformer
load (VA)for this value of ZLD?
Solution:
EE301 Lesson 29 Reading: 22.4
3
Example 3 An amplifier is modeled with a Thvenin equivalent
impedance of 320-160j . A transformer is used to impedance match
the load to the source to ensure max power transfer. (a) What turns
ratio should be chosen for the transformer, and what value of load
resistance should be chosen to ensure max power transfer? (b) What
is the real and reactive power of the load? What is the real and
reactive power delivered by the source?
Solution:
Reflected Impedance Transformers make load impedances look bigger
or smaller depending on their turns ratio. ZP refl is the impedance
that appears at the primary windings.In the circuit shown above on
the left, what impedance does the primary-side source see due to
the impedance on the secondary side?The term a2Zsec is referred to
as the loads reflected impedance.Power Supply Transformers Power
supply transformers are used to convert incoming 120 Vac to
voltages of various levels necessary for different
circuits.Transformers for Power SystemsImpedance Matching
Transformers are used to raise or lower the apparent impedance in
order to achieve maximum power transfer.Example 2 An amplifier is
modeled with a Thvenin equivalent impedance of 36-54j (.(a) What
load impedance must be chosen to ensure maximum power transfer
occurs?Example 3 An amplifier is modeled with a Thvenin equivalent
impedance of 320-160j (. A transformer is used to impedance match
the load to the source to ensure max power transfer.
