Why and How we use Maximum Power Transfer Theorem

1. (Series of Lectures for DAE / B-Tech / BS
Electrical)
Presented by. Engr. Fazal Ur Rehman
Lecturer Electrical GPI Karak
Former HOD Electrical RPI, Rwp

2.  NEED.
 In Communication circuits if we need to transfer
maximum power from source (Transmitter) to
Load ( Receiver) then it can be made possible
via implementation of MPTT.


3.  Maximum power will transferred from source
to load if the source impedance is equal to
load impedance.
OR
 Maximum power is delivered to the load
when the load resistance is equal to the
internal resistance of a source.

5.  The original two terminal circuit is replaced
with a Thevenin’s equivalent circuit across
the variable load resistance. The current
through the load for any value of load
resistance is

6.  For maximum transfer of power the load
resistance (RL as shown in the figure) must be
equal to source resistance (RTh in this case)
 Note. RTh will be found out by using Thevinine
Theorem. (will be discussed in the upcoming
lectures)
 The maximum power
Delivered to the load is.
 The maximum power
Transferred from source is.
PT = IL
2 (RTH + RL)
= 2 IL
2 RL

7.  It can be shown by power transfer curve shown
below;
 The efficiency under the condition of maximum
power transfer is
Efficiency = Output / Input × 100
= IL
2 RL / 2 IL
2 RL × 100
= 50 %

9.  Step 1. Eliminate the load element from the
circuit.
 Step 2. Find the VTh on load terminals.
 Step 3. Secondly sources are assigned zero.
 voltage source= short circuited
 Current Source = Open Circuited.
 Step 4. Then Calculate Total Resistance of the
remaining circuit. Mark it RTh.
 Finally Connect VTh and RTh in series and
reconnect your load.
 Then find Pmax at the end using Superposition
Theorem.
Pmax = V2
TH / 4 RTH

11.  Will there be maximum transfer of power
from audio amplifier to loudspeaker???
 Answer is…