An apparatus comprising: a switching power supply circuit configured and arranged to: operate in a high-power mode by connecting high and low power rails of a first circuit to a first output and a ground output, respectively, of a power source circuit, and by connecting high and low power rails of a second circuit to a second output and the ground output, respectively, of the power source circuit, wherein the second output is a one of common with and different from the first output, and operate in a low-power mode in which the first circuit is operated in a high power domain and in which the second circuit is operated in a low power domain using recycled charge from the high power domain, by connecting the high power rail of the first circuit to the first output of the power supply circuit, the low power rail of the first circuit to the high power rail of the second circuit, and the low power rail of the second circuit to the ground output of the power supply; a control circuit configured and arranged to respond to a control signal by switching the switching circuit between the high-power mode and the low-power mode for power conservation; and characterized by a mode control circuit configured and arranged with the switching circuit and the control circuit to: monitor accesses to the first and second circuit (130, 140); provide the control signal for operating the switching power supply circuit in the high-power mode in response to a request for access to one of the first circuit and the second circuit (130, 140); and provide the control signal for operating the switching power supply circuit in the low-power mode in a power conservation state in response to a lack of access requests for one of the first circuit and the second circuit over a predefined time period. a switching power supply circuit configured and arranged to: operate in a high-power mode by connecting high and low power rails of a first circuit to a first output and a ground output, respectively, of a power source circuit, and by connecting high and low power rails of a second circuit to a second output and the ground output, respectively, of the power source circuit, wherein the second output is a one of common with and different from the first output, and operate in a low-power mode in which the first circuit is operated in a high power domain and in which the second circuit is operated in a low power domain using recycled charge from the high power domain, by connecting the high power rail of the first circuit to the first output of the power supply circuit, the low power rail of the first circuit to the high power rail of the second circuit, and the low power rail of the second circuit to the ground output of the power supply; operate in a high-power mode by connecting high and low power rails of a first circuit to a first output and a ground output, respectively, of a power source circuit, and by connecting high and low power rails of a second circuit to a second output and the ground output, respectively, of the power source circuit, wherein the second output is a one of common with and different from the first output, and operate in a low-power mode in which the first circuit is operated in a high power domain and in which the second circuit is operated in a low power domain using recycled charge from the high power domain, by connecting the high power rail of the first circuit to the first output of the power supply circuit, the low power rail of the first circuit to the high power rail of the second circuit, and the low power rail of the second circuit to the ground output of the power supply; a control circuit configured and arranged to respond to a control signal by switching the switching circuit between the high-power mode and the low-power mode for power conservation; and characterized by a mode control circuit configured and arranged with the switching circuit and the control circuit to: monitor accesses to the first and second circuit (130, 140); provide the control signal for operating the switching power supply circuit in the high-power mode in response to a request for access to one of the first circuit and the second circuit (130, 140); and provide the control signal for operating the switching power supply circuit in the low-power mode in a power conservation state in response to a lack of access requests for one of the first circuit and the second circuit over a predefined time period.