Power transfer device, power supply device and power receiving device

1. A power transfer device comprising:

a transformer that couples a primary circuit and a secondary circuit and has a coupling constant of less than one; and

capacitances that are respectively provided in the primary circuit and the secondary circuit, and connected in series with coils that form the transformer, wherein

circuit constants of the primary circuit and the secondary circuit are set so that the primary circuit and the secondary circuit resonate at the same frequency and a product of the square of the coupling constant, a Q value of the primary circuit and a Q value of the secondary circuit is one, and

the primary circuit transfers power to the secondary circuit by means of the transformer, using a carrier wave having the resonance frequency.

2. A power transfer device comprising:

a first transformer that couples a primary circuit and a secondary circuit and has a coupling constant of less than one;

a second transformer that couples the secondary circuit and a tertiary circuit; and

capacitances that are respectively provided in the primary circuit, the secondary circuit and the tertiary circuit, and connected in series with coils that form one of the first transformer and the second transformer, wherein

circuit constants of the primary circuit, the secondary circuit and the tertiary circuit are set so that the primary circuit, the secondary circuit and the tertiary circuit resonate at the same frequency and a product of the square of the coupling constant of the first transformer, an inductance and a resistance of the primary circuit is equal to a product of the square of a coupling constant of the second transformer, an inductance and a resistance of the tertiary circuit, and

the primary circuit transfers power to the tertiary circuit via the secondary circuit by means of the first transformer and the second transformer, using a carrier wave having the resonance frequency.

3. The power transfer device according to claim 1 or 2 , wherein

the primary circuit further includes an oscillator circuit including an amplifier in which an output current is positively feedbacked at the resonance frequency through a resonance circuit including the coil and the capacitance.

4. The power transfer device according to claim 3 , wherein

an amplification factor of the amplifier is at least two.

5. The power transfer device according to claim 3 , wherein

the amplifier is connected to the resonance circuit so that all the output current passes through the resonance circuit.

6. The power transfer device according to claim 1 or 2 , wherein

the transformer has no magnetic material core that, forms a closed magnetic circuit.

7. The power transfer device according to claim 1 or 2 , wherein

the primary circuit modulates the carrier wave in order to transfer information together with power.

8. The power transfer device according to claim 2 , wherein

the tertiary circuit, further includes a full-wave rectification circuit that full-wave rectifies power obtained by the second transformer, and

the capacitance of the tertiary circuit is arranged between the coil that forms the second transformer and the full-wave rectification circuit.

9. The power transfer device according to claim 8 , wherein

the full-wave rectification circuit is formed by a plurality of active elements.

10. A power supply device comprising:

a primary circuit including

a coil that forms a transformer having a coupling constant of less than one with a coil of a power receiving device to be coupled with, the power receiving device having a secondary circuit that includes the coil and a capacitance connected in series, and

a capacitance that is connected In series with the coil of the primary circuit, wherein

a circuit constant of the primary circuit is set so that the primary circuit and the secondary circuit resonate at the same frequency and a product of the square of the coupling constant, a Q value of the primary circuit and a Q value of the secondary circuit is one, and

the primary circuit transfers power to the secondary circuit by means of the transformer, using a carrier wave having the resonance frequency.

11. A power receiving device comprising:

a secondary circuit including

a coil that forms a transformer having a coupling constant of less than one with a coil of a power supply device to be coupled with, the power supply device having a primary circuit that includes the coil and a capacitance connected in series, and

a capacitance that is connected in series with the coil of the secondary circuit, wherein

a circuit constant of the secondary circuit is set so that the primary circuit and the secondary circuit resonate at the same frequency and a product of the square of the coupling constant, a Q value of the primary circuit and a Q value of the secondary circuit is one, and

the secondary circuit receives power that is transferred from the primary circuit by means of the transformer using a carrier wave having the resonance frequency.

12. A power supply device comprising:

a primary circuit including

a coil that forms a first transformer having a coupling constant of less than one with a coil of a secondary circuit of a power receiving device to be coupled with, the power receiving device having a secondary circuit and a tertiary circuit that each include a coil and a capacitance connected in series and that are coupled via a second transformer, and

a capacitance that is connected in series with the coil of the primary circuit, wherein

a circuit constant of the primary circuit is set so that the primary circuit, the secondary circuit and the tertiary circuit resonate at the same frequency and a product of the square of the coupling constant of the first transformer, an inductance and a resistance of the primary circuit is equal to a product of the square of the coupling constant of the second transformer, an inductance and a resistance of the tertiary circuit, and

the primary circuit transfers power to the tertiary circuit via the secondary circuit by means of the first transformer and the second transformer, using a carrier wave having the resonance frequency.

13. A power receiving device comprising:

a secondary circuit including

a first coil that forms a first transformer having a coupling constant of less than one with a coil of a power supply device to be coupled with, the power supply device having a primary circuit that includes the coil and a capacitance connected in series, and

a capacitance that is connected in series with the first coil; and

a tertiary circuit including

a third coil that forms a second transformer with a second coil of the secondary circuit to be coupled with, the second coil being connected in series with the first coil, and

a capacitance that Is connected in series with the third coil, wherein

circuit constants of the secondary circuit and the tertiary circuit are set so that the primary circuit, the secondary circuit and the tertiary circuit resonate at the same frequency and a product of the square of the coupling constant of the first transformer, an inductance and a resistance of the primary circuit is equal to a product of the square of a coupling constant of the second transformer, an inductance and a resistance of the tertiary circuit, and

the tertiary circuit receives power that is transferred from the primary circuit via the secondary circuit by means of the second transformer using a carrier wave having the resonance frequency.