Abstract: A power system, power circuit, and methods for maintaining or providing a constant or substantially constant power source and for reducing and/or minimizing power decay of a predetermined component are provided. Such improvement of power delivery and minimization of power loss is important for precision instrumentation applications. One such application is the infrared (“IR”) source driver for a Fourier Transform Infrared Spectrometer (“FTIR”). The power system and/or circuit may include two integrated circuits in a novel way to make an efficient constant power IR source driver. The method may include having a switching regulator comparing a sample of output voltage with a reference voltage, a second element computing, calculating and/or creating a voltage that is a product of another voltage and a current to obtain a signal proportional to delivered power, and operating a closed loop regulator to provide a constant delivered power to the source.