maximum power transfer theorem 1 maximum power transfer theorem in many electrical and electronic...

Maximum Power Transfer Theorem

1

MAXIMUM POWER TRANSFER THEOREM

• In many electrical and electronic applications, we are interested in the amount of power received by a particular load (speaker, electric motor, antenna)

• Electric systems are a source of power and a load connected to that source

• Sources – Amplifiers, generators, power supplies

• All linearly constructed sources can be reduced to their Thevenin equivalent

• In DC circuits, the load can be represented by a resistance RL

Maximum Power Transfer Theorem

2

POWER DELIVERED TO LOAD

LLLLLLL RVRIIVP 22

• The source develops a voltage VL across the load and enables current IL to flow into it

• The power delivered to the load resistance (RL) depends on the value of RL

E T H

R T H

R L

IL

V L

+

-

T h e v e n in e quiv a le n tc ir c uit

L o a d

So ur c e

Maximum Power Transfer Theorem

3

MAXIMUM POWER, CURRENT AND VOLTAGE CONDITIONS

• Maximum current IL occurs when RL = 0 (shorted terminals)

• The maximum voltage VL occurs when RL = (open circuited terminals)

• Yet load power PL = 0 for both cases

• PL is maximum when RL equals the Thevenin equivalent resistance of the source, I.e. when RL = RTH

• The maximum power transfer theorem is thus:

• Maximum power is developed in a load when the load resistance equals the Thevenin resistance of the source to which it is connected

• Maximum power is delivered when VL = ETH/2

• Thus

TH

TH

L

LL R

E

R

VP

4(max)

22