US Patent 7425728 Surface light source control device

A surface light source control device has a plane light source control circuit for setting a current amount to a plurality of diode arrays. The light source control circuit comprises a constant current circuit for holding currents respectively flowing in the plurality of diode arrays constant at the same current value; and a power supply voltage control loop for selecting a notable diode array with a minimum reference voltage, among reference voltages appearing at each terminal of the plurality of diode arrays, appeared thereon to select the minimum reference voltage by a voltage selection circuit and adjusting a common power supply voltage so that the reference voltage becomes a prescribed value.