![]() Maximum power transfer does not coincide with the goal of the lowest noise. As a ratio, “output impedance”: “load impedance” is known as damping factor, typically in the range of 100 to 1000. Similar to AC power distribution, high fidelity audio amplifiers are designed for a relatively low output impedance and a relatively high speaker load impedance. The goal of high efficiency is more important for AC power distribution, which dictates a relatively low generator impedance compared to the load impedance. ![]() Application of The Maximum Power Transfer theorem to AC power distribution will not result in maximum or even high efficiency. The Maximum Power Transfer Theorem does not: Maximum power transfer does not coincide with maximum efficiency. Maximum Power Doesn’t Mean Maximum Efficiency Practical applications of this might include radio transmitter final amplifier stage design (seeking to maximize the power delivered to the antenna or transmission line), a grid-tied inverter loading a solar array, or electric vehicle design (seeking to maximize the power delivered to drive motor). Having reduced a network down to a Thevenin voltage and resistance (or Norton current and resistance), you simply set the load resistance equal to that Thevenin or Norton equivalent (or vice versa) to ensure maximum power dissipation at the load. If you were designing a circuit for maximum power dissipation at the load resistance, this theorem would be very useful. Likewise, if we increase the load resistance (1.1 Ω instead of 0.8 Ω, for example), power dissipation will also be less than it was at 0.8 Ω exactly: Power dissipation increased for both the Thevenin resistance and the total circuit, but it decreased for the load resistor. If we were to try a lower value for the load resistance (0.5 Ω instead of 0.8 Ω, for example), our power dissipated by the load resistance would decrease: ![]() With this value of load resistance, the dissipated power will be 39.2 watts: Taking our Thevenin equivalent example circuit, the Maximum Power Transfer Theorem tells us that the load resistance resulting in greatest power dissipation is equal in value to the Thevenin resistance (in this case, 0.8 Ω): A load impedance that is too low will not only result in low power output but possibly overheating of the amplifier due to the power dissipated in its internal (Thevenin or Norton) impedance. A load impedance that is too high will result in low power output. Impedance, the overall opposition to AC and DC current, is very similar to resistance and must be equal between source and load for the greatest amount of power to be transferred to the load. This is essentially what is aimed for in radio transmitter design, where the antenna or transmission line “impedance” is matched to final power amplifier “impedance” for maximum radio frequency power output. If the load resistance is lower or higher than the Thevenin/Norton resistance of the source network, its dissipated power will be less than the maximum. Simply stated, the maximum amount of power will be dissipated by a load resistance when that load resistance is equal to the Thevenin/ Norton resistance of the network supplying the power. The above discussion has proved that the load impedance Z L should be the conjugate of the source internal Impedance Z i to have maximum power delivered to the load.The Maximum Power Transfer Theorem is not so much a means of analysis as it is an aid to system design. Power dissipated in the load resistor R, is P$_$ should be: Where Rth and Vth are fixed and we want to change the load resistor R such that the load gets maximum power dissipation. Suppose the following complex circuit is reduced to Thevenin’s resistor and Thevenin’s voltage source. Maximum Power Transfer Theorem Explanation with Example A Brief Guide About Electronic Oscillator and their Different Types.7 Safety Precautions to Take When Doing Electrical Repair at Home.Thévenin’s resistor act as the source internal resistor. In the case of a more complex circuit, the load resistor should be equal to Thevenin’s resistor after applying Thevenin’s theorem to the circuit. In the Thevenin Theorem and Norton Theorem, we observed that any linear circuit can be reduced to a single source and single resistor except load resistor. The efficiency will always be increased by decreasing source internal resistance. Efficiency is the ratio of power dissipated in load and power provided by the source. Efficiency is something different than power dissipation in load.
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