Patent ID: 7541690

Claim:
A signal transmission method for transmitting a signal between a regulated power supply unit that operates and controls a high intensity discharge lamp and a setting unit that gives various kinds of commands to the regulated power supply unit, the method comprising the steps of: providing the regulated power supply unit with a first communication controller that receives the command from the setting unit to control the high intensity discharge lamp based on the command and transmits operation state information of the high intensity discharge lamp to the setting unit; providing the setting unit with a second communication controller that transmits the command to the regulated power supply unit and receives operation state information of the high intensity discharge lamp to execute processing appropriate to the operation state information; providing a pair of signal lines that interconnect the regulated power supply unit and the setting unit via a transmission photo-coupler and a reception photo-coupler; implementing ON/OFF control of the transmission photo-coupler by a lighting acknowledgement signal that has a predetermined frequency and a predetermined duty ratio and is continuously sent out from a transmission terminal of the first communication controller when the high intensity discharge lamp has been lit normally based on a lighting command transmitted from the setting unit to the regulated power supply unit, and transmitting an output signal of the transmission photo-coupler associated with the ON/OFF control to the second communication controller via the signal lines; and transmitting the command sent out from a transmission terminal of the second communication controller to the first communication controller via the signal lines and the reception photo-coupler during an OFF-period of the transmission photo-coupler.