A user system is provided including a plurality of flash memory devices and a memory controller connected to the flash memory devices through a plurality of channels. The memory controller includes a voltage regulator configured to supply a power of the flash memory devices and a compensation unit configured to supply an additional power to the flash memory devices when a power required by the flash memory devices exceeds a predetermined level. The compensation unit includes a resistor unit connected to an output terminal of the voltage regulator and input terminals of the flash memory devices and a charging unit connected to input terminals of the flash memory devices. The charging unit is configured to supply an additional power to the flash memory devices according to voltages of input terminals of the flash memory devices.