POWER SUPPLY ADAPTER, ELECTRONIC EQUIPMENT, AND SIGNAL TRANSMISSION SYSTEM

PROBLEM TO BE SOLVED: To transmit signals between an AC adaptor and an electronic equipment, with these two equipment being connected by two terminals, that is, a positive terminal and a negative terminal. SOLUTION: In an AC adaptor, a switching circuit 54 is in an on-state and therefore a large power circuit 53 starts operation. In a set, a switching circuit 64 is turned into an off-state by a control circuit 62 through a stop circuit 63. In the set, when the off-state of the switching circuit 64 is detected by a current detecting circuit 51, the switching circuit 54 is turned into an off-state and operation is started only by a small power circuit 52. At this time, the AC adaptor is in a state capable of receiving signals from the set. In the set, the control circuit 62 controls a signal transmitting circuit 65 to control the on/off operation of a switching circuit 66, and thus signals are transmitted to the AC adaptor.