There are circuits for constant controlled voltage, and constant controlled current as shown below:
Voltage controlled constant current source
Voltage controlled constant voltage source
simulate this circuit – Schematic created using CircuitLab
What if I wanted to create a circuit that was a voltage controlled constant power source? Here is the basic idea, I'm wondering if anyone has used a circuit that does this sort of thing, or if there are circuits that do this. I have not found any yet. I would like to control the power going into a load.
Best Answer
Here is an application note circuit that may be useful. The power monitor chip is more economical than an analog multiplier and allows the load to be grounded, which is a big advantage in many applications.
As it says in the app note, the circuit can be scaled easily and the simple linear output stage could be replaced with a SMPS block.
The circuit controls the power to the load in parallel with the divider so it tails off a bit at high load resistances, but it's still not too shabby even at the 100mW output level.
Your circuit looks conceptually okay, concerns would include the input voltage range of the instrumentation amplifier and its common-mode rejection. Stability is the most likely thing to cause headaches in many of these circuits.