A switched-mode power supply (SMPS), or a “switching” power supply or voltage regulator, can include a power stage circuit and a control circuit. The power stage circuit can include one or more power devices. When an input voltage is applied, the control circuit can consider internal parameters and external load changes, and may regulate the on/off times of the switch system in the power stage circuit. In this way, the output voltage and/or the output current of the switching power supply can be maintained as substantially constant. Elements in the power stage circuit and/or control circuit can be fabricated in a semiconductor wafer.