Electrical Engineering ⇒ Topic : Maximum Power Transfer Theorem with d.c

Maximum Power Transfer Theorem  with d.c

Many circuits basically consist of sources, supplying voltage, current, or power to the load; for example, a radio speaker system, or a microphone supplying the input signals to voltage pre-amplifiers. Sometimes it is necessary to transfer maximum voltage, current or power from the source to the load. In the simple resistive circuit shown in Fig. (a), Rs is the source resistance. Our aim is to find the necessary conditions so that the power delivered by the source to the load is maximum.

It is a fact that more voltage is delivered to the load when the load resistance is high as compared to the resistance of the source. On the other hand, maximum current is transferred to the load when the load resistance is small compared to the source resistance.

For many applications, an important consideration is the maximum power transfer to the load; for example, maximum power transfer is desirable from the output amplifier to the speaker of an audio sound system. The maximum Power Transfer Theorem states that maximum power is delivered from a source to a load when the load resistance is equal to the source resistance. In Fig. (a),assume that the load resistance is variable.

                                                               figure (a)

To determine the value of R_L for maximum power to be transferred to the load, we have to set the first derivative of the above equation with respect to R_L, i.e. 

So, maximum power will be transferred to the load when load resistance is equal to the source resistance