advertisement

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 1 POWER DELIVERED TO LOAD T hevenin equivalent circuit RTH IL + ETH VL RL Load Source • The source develops a voltage VL across the load and enables current IL to flow into it PL V L I L I L R L V L R L 2 • 2 The power delivered to the load resistance (RL) depends on the value of RL Maximum Power Transfer Theorem 2 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 2 PL (max) VL RL 2 E TH 4 R TH Maximum Power Transfer Theorem 3