# Concept Question about Maximum Power Transfer (More than cursory)

#### snipe

Joined Dec 13, 2010
1
Hi All,
This is my first my first post, but I am a long time fan of the site, and I am running into a wall with a problem at work.

My question is, does Maximum Power Transfer (MPT) apply to DC current sources?

Can a DC current source be damaged, if it is continuously cycled, while NOT achieving MPT?

Further more, will MPT apply to the "apparent resistance" of a series of forward biased PN junctions?

I hope the real questions don't get lost in the problem explanation, but here is an overview of the problem:

There is a DC current source, sourcing 15A, to 54 series connected PN junctions in a forward biased configuration. When applying this circuit, the voltage on the current supply settles at around 39.85 vDC. We are applying this power for a minute or two to slightly heat up the PN junction, and then examining them with an infrared camera, in a mass production environment. So, 15A @ ~40v is a resistance of around 2.6Ohms for all of the PN junctions.

Also, looking at it from the perspective of the PN junctions, if each PN has a voltage drop of 0.707v, times 54 is 38.18v. This is close to what I'm observing. Applying Ohm's law we find that the resistance should be in the range of 38.18v/15A ~= 2.54Ohms. This is also very close to what I'm observing.

So, with this configuration, using a DC current source, would I be able to design a resistive network, or implement a matching transformer, to transfer maximum power to the load? It seems more complicated since a current source model has a large resistance in parallel, while a voltage source has a small resistance in series....

OR.... Am I forgetting a fundamental, and I'm chasing a ghost? Does MPT not apply to DC current sources? I haven't been able to find much information about this situation.

Thanks

#### Jony130

Joined Feb 17, 2009
5,127
Hmm, well I think that MPT don't apply to current source simply becaues current source exist only in circuit theory.
In real life current source are active device supply form the voltage source.
So there is the limit of max power you can apply to the load.
P_max = (Vcc - V_headroom ) * Isc.
And why you even bother yourself with MPT ? MTP is important in high frequency circuit.