A power circuit includes a first charge pump for converting a supply voltage into a first high voltage and a first low voltage, at least one second charge pump, each for increasing the first high voltage by a first variance value to a second high voltage, and at least one third charge pump, each for decreasing the first low voltage by a second variance value to a second low voltage. A difference between the first high and low voltages is less than a breakdown threshold. The second and third variance margins are less than the breakdown threshold.