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A non-contact power supply system includes a power supply device for transmitting high frequency power and a load device which receives the high frequency power in a non-contact mode by electromagnetic induction to supply it to a load. The power supply device includes a power transmission unit havin

A non-contact power supply system includes a power supply device for transmitting high frequency power and a load device which receives the high frequency power in a non-contact mode by electromagnetic induction to supply it to a load. The power supply device includes a power transmission unit having a primary power coil and an inverter circuit, an inquiry unit having at least one primary signal coil and an oscillation circuit, a signal detection unit and a control unit. The load device includes a power reception unit having a secondary power coil magnetically coupled to the primary power coil and a power conversion unit, a secondary signal coil magnetically coupled to the primary signal coil, and a response unit which is operated by electromotive force induced in the secondary signal coil. The control unit stops power transmission when no signal is detected and executes power transmission which a signal is detected.

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1. A non-contact power supply system comprising: a power supply device for transmitting high frequency power; anda load device which contactlessly receives the high frequency power transmitted from the power supply device by electromagnetic induction to supply the high frequency power to a load,wher

1. A non-contact power supply system comprising: a power supply device for transmitting high frequency power; anda load device which contactlessly receives the high frequency power transmitted from the power supply device by electromagnetic induction to supply the high frequency power to a load,wherein the power supply device includes a power transmission unit having a primary power coil for power transmission and an inverter circuit for supplying high frequency current to the primary power coil; an inquiry unit having a primary signal coil for receiving a signal from the load device and an oscillation circuit, the primary signal coil being connected between output terminals of the oscillation circuit; a signal detection unit for detecting the signal received by the primary signal coil; and a control unit for controlling the power transmission unit according to the signal detected by the signal detection unit,wherein the load device includes the load; a power reception unit having a secondary power coil for power reception which is magnetically coupled to the primary power coil and a power conversion unit which converts the high frequency power induced in the secondary power coil into power for the load; a secondary signal coil which is magnetically coupled to the primary signal coil; and a response unit which is operated by an electromotive force induced in the secondary signal coil to transmit the signal from the secondary signal coil,wherein the control unit of the power supply device does not execute the power transmission from the power transmission unit when the signal detection unit does not detect the signal and executes the power transmission from the power transmission unit when the signal detection unit detects the signal, andwherein the oscillation circuit of the inquiry unit oscillates at a frequency higher than that of the inverter circuit, and the response unit has a power circuit which produces operation power from a voltage induced in the secondary signal coil and a modulation circuit which is operated by the operation power produced by the power circuit to output a modulation signal of a frequency lower than that of the inverter circuit to the secondary signal coil. 2. The non-contact power supply system of claim 1, wherein the primary power coil and the primary signal coil are substantially coaxially arranged in the power supply device, and the secondary power coil and the secondary signal coil are substantially coaxially arranged in the load device. 3. The non-contact power supply system of claim 1, wherein the control unit of the power supply device drives the inverter circuit intermittently, when it executes the power transmission from the power transmission unit and stops the power transmission from the power transmission unit if the signal detection unit does not detect the signal during a pause period of the inverter circuit. 4. The non-contact power supply system of claim 3, wherein the signal is an amplitude modulated signal and the signal detection unit of the power supply device detects an envelope of voltage induced in the primary signal coil and determines that the signal is detected if a detected voltage level exceeds a threshold value. 5. The non-contact power supply system of claim 1, wherein the load device includes a load device control unit for transmitting a control command from the response unit to the control unit of the power supply device to instruct stop of the power transmission from the power transmission unit or reduction of transmission power. 6. The non-contact power supply system of claim 1, wherein the control unit of the power supply device does not execute the power transmission from the power transmission unit if a signal level detected by the signal detection unit is constant. 7. The non-contact power supply system of claim 1, wherein the modulation circuit produces the signal modulated by varying an impedance of an impedance element connected between the two ends of the secondary signal coil. 8. The non-contact power supply system of claim 1, wherein the power reception unit of the load device further has a power circuit for producing operation power of the response unit from the high frequency power induced in the secondary power coil. 9. The non-contact power supply system of claim 1, wherein the signal detection unit of the power supply device further has one or more additional primary signal coils. 10. The non-contact power supply system of claim 1, further comprising additional one or more load devices, wherein the load device and the additional load devices have different types of loads and response units of the load device and the additional load devices transmit and receive signals of different frequencies according to the types of the loads, and wherein the inquiry unit of the power supply device allows the oscillation circuit to oscillate at frequencies varying according to the types of the load device and the additional load devices. 11. The non-contact power supply system of claim 1, wherein the load device further includes an additional power circuit for producing operation power of the response unit from high frequency power induced in the secondary power coil and a load device signal transmission unit operated by the power produced by the additional power circuit to transmit a transmission signal, and the power supply device includes a power supply device signal reception unit for receiving the transmission signal from the load device signal transmission unit. 12. The non-contact power supply system of claim 1, wherein the power supply device further includes a modulation circuit for modulating the high frequency power from the power transmission unit by an information signal and the load device further includes a demodulation circuit for demodulating high frequency power induced in the secondary power coil to recover the information signal. 13. The non-contact power supply system of claim 1, wherein the oscillation circuit oscillates intermittently while the signal detection unit does not detect the signal and the oscillation circuit continuously oscillates if the signal detection unit detects the signal. 14. The non-contact power supply system of claim 2, wherein an inner and an outer diameter of the primary signal coil are substantially identical to those of the secondary signal coil and the inner diameter of the secondary signal coil is larger than an outer diameter of the secondary power coil. 15. The non-contact power supply system of claim 2, wherein the primary signal coil and the secondary signal coil are arranged between the primary power coil and the secondary power coil while the primary power coil and the secondary power coil are magnetically coupled to each other. 16. The non-contact power supply system of claim 1, wherein the load device includes a response signal transmission unit which is operated by the high frequency power induced in the secondary power coil to transmit a response signal through the secondary power coil, wherein the power supply device includes a response signal reception unit for receiving the response signal through the primary power coil magnetically coupled to the secondary power coil, andwherein when the control unit of the power supply device executes the power transmission from the power transmission unit according to the signal detected by the signal detection unit, the control unit stops the power transmission from the power transmission unit if a period in which the response signal reception unit receives no response signal exceeds a specific period and the control unit continues the power transmission from the power transmission unit if the period in which the response signal reception unit receives no response signal does not exceed the specific period. 17. The non-contact power supply system of claim 16, wherein the load device includes a load device control unit for transmitting a control command from the response unit and the response signal transmission unit to the control unit of the power supply device to instruct stop of the power transmission from the power transmission unit or reduction of transmission power.