A dual-voltage secure digital (SD) card can be inserted into a legacy host or a newer host. Legacy hosts drive a high voltage such as 3.3 volts onto the power line of the SD bus, while newer hosts drive the power line with a reduced voltage such as 1.8 volts. A flash and voltage controller chip on the SD card has a controller core that operates at the reduced voltage. A voltage regulator on the SD card, or a power management unit inside the controller chip generates an internal power voltage of 1.8 volts from the dual-voltage SD bus power line. The internal power voltage is applied to the controller core and to a voltage converter that generates a flash power voltage from the internal power voltage. The flash power voltage is applied to flash-memory chips on the SD card that operate at the higher voltage.