For some reason, I need a Time-Variable DC power source that changes it's value according to time. I need this changing of value to be controllable. I'll put it this way : Say I have a 12 volt DC power source like a car battery. In some point of time I need this value to be changed to 11 volts, then to 9 volts...etc to zero volts. Then start the cycle backwards from zero to 1 volt, then it increases to reach 12 volts and this process is time-controlled and time-based. I am somehow familiar with buck converters, and I know they step down the supplied voltage, but I want this step down and then backward cycle of reaching up the supplied voltage to be time-controlled. I need to be able to control the whole cycle of this time-variable DC source.
The question is: Does such a circuit exist? And if yes what are those circuits called?
Notice that I didn't specify any info about wattage or ampere for the circuit, but if this was a problem then I guess the example I presented gives some hints: 12 volts source power varying to zero then cycles backwards from zero to 12 volts. Efficiency is needed as high as possible.
Thanks for contributing in any ideas that helps design or clarify the nature of the required circuit.