Patent ID: 8352755

Claim:
A digital image system comprising a host device, a transmission/reception reinforcement device a display device which the host device transmits digital image data to the display device through the transmission/reception reinforcement device, wherein the transmission/reception reinforcement device comprises a first power-supply switching unit or a second power-supply switching unit, and each of the first power-supply switching unit and the second power-supply switching unit comprises: an external power-supply input terminal to which a separate external power-supply voltage is input; an internal power-supply input terminal connected with one internal power-supply line out of communication lines between the host device and the display device; a power-supply output terminal from which the external power-supply voltage from the external power-supply input terminal or an internal power-supply voltage from the internal power-supply input terminal is output; and a switch which enters an ON state when he external power-supply voltage from the external power-supply input terminal becomes lower than a predetermined voltage, and the external power-supply voltage is applied to the power-supply output terminal when the switch is in an OFF state and the internal power-supply voltage from the internal power-supply input terminal is applied to the power-supply output terminal when the switch is in the ON state, wherein in each of the first power-supply switching unit and the second power-supply switching unit, the switch is a p-channel field effect transistor, the external power-supply input terminal is connected to an anode of a first diode and a gate of the p-channel field effect transistor, a cathode of the first diode is connected to the power-supply output terminal, the internal power-supply input terminal is connected to a source of the p-channel field effect transistor, a drain of the p-channel field effect transistor is connected to an anode of a second diode, and a cathode of the second diode is connected to the power-supply output terminal.