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practically how to apply Maximum power theorem by just looking the circuit

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rajaram04

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Hello sir
Please clarify about how maximum power transfer theorem is applied to circuits by looking to them very quickly if one is doing his own practical homely ?
Where it finds the use actually ? As we studied only theory based things for exams so unable to use in daily life & then all gone to scraps :-(
please help me in a practical way with a very clean & short example
 

SunnySkyguy

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maximal power transfer is used everywhere where source and load impedances are matched.

such as engineering instruments are 50 ohms for a few reasons, one being maximum power transfer..

Radio transmitters to antenna match all impedances to day same and also minimize reflections which is measured by VSWR or Return Loss.

We don't use it for power sources or audio amps for this because if the load impedance was reduced down to the power source impedance, it would cause over-current or regulation or dampening factor issues. but the ratio of load to source impedance is an important factor in everything related to power where you must also include the ESR and ESL of each component.

When I power LEDs from a CV source and want to match LEDs for parallel operation I know the power sources is much lower than the ESR of a power LED, I know it is not safe to parallel each diode without a series resistor. I learned this is due to ESR of the LEDs and differences in PN junction drop due to self heating. My experience told me maximum power transfer ought to be when parallel devices had matched ESRs so I only added the min-max difference from the specs or experience using the VI curve to calculate ESR. This means if you had a 0 ohm source and 0 ohm ideal diode, I was choosing an external resistor close to the ESR of the LED to minimize wasted resistor voltage drop down to 0.1 or 0.2V. I usually only do this with strings of 4 or more in parallel. Its not exactly the same as this theorem, but it is related to Shockley effect and thermal resistance and how to get maximum power transfer without thermal runaway with the minimum loss using passive components only.

In home projects with motors and batteries and LEDs, Keep in mind the battery ESR to load ESR ratio when trying to maximize the power transfer from battery to load. When losses at maximum power transfer are consider, you will find matching these ESR in battery and load as a starting point for analysis for stability when the voltages are matched.
 
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rajaram04

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Nice one sir , what is ESR & ESL here ?
 

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