A burst oscillation circuit operates switches in a burst oscillation mode based on a feedback signal. A first burst operation cancellation threshold voltage comparator compares a first burst operation cancellation threshold voltage set higher than a voltage of the feedback signal that a load current reaches the standby threshold and a voltage of the feedback signal, and outputs a first output signal. A second burst operation cancellation threshold voltage comparator compares a second burst operation cancellation threshold voltage set lower than the voltage of the feedback signal that the load current reaches the standby threshold and higher than a voltage of the feedback signal during a non-oscillation period of the burst oscillation operation and the voltage of the feedback signal and outputs a second output signal. A standby cancellation circuit generates a standby cancel signal to cancel the standby state based on the first and second output signal.

A first switch and a second switch connected in series to both terminals of a DC power source. A signal generation circuit generates a feedback signal based on the DC voltage detected by the voltage detection circuit, and outputs the feedback signal, the feedback signal for turning the first and second switches on and off. A burst oscillation circuit that generates a burst oscillation signal based on a feedback signal and turns the first switch element and the second switch element on and off based on the burst oscillation signal when the standby state is detected. The burst oscillation circuit comprises a capacitor and a rapid charge circuit. When this device returns from standby state to normal state, the rapid charging circuit charges the capacitor after the feedback signal exceeds the cancellation threshold voltage.

A power conversion device, which includes an insulation type full bridge converter and can switch a power transmission direction at a high speed, is provided. A DC/DC converter (10) constitutes a power conversion device, which operates as a first type converter that converts a voltage within a first range applied to a first input/output terminal pair into a voltage within a second range and outputs the voltage from a second input/output terminal pair or a second type converter that converts a voltage within the second range applied to the second input/output terminal pair into a voltage within the first range and outputs the voltage from the first input/output terminal pair, as a device that performs a predetermined state transition of the DC/DC converter (10) after waiting for a load current value of a primary or secondary side of a transformer (TR) becomes a value within a predetermined current value range.

The invention relates to a gate unit (22) for controlling a gate commutated thyristor (21), comprising: a voltage selector (26) for selectively applying a high supply potential (V.sub.pos), a middle supply potential (V.sub.mid), and a low supply potential (V.sub.neg); a nonlinear inductor (27) serially coupled between the output of the voltage selector (26); a gate control unit (23) configured to control the voltage selector (26) to control switching of the gate commutated thyristor (21) in its turn-on state comprising a turn-on pulse generation, a positive-gate-voltage backporch operation, a negative-gate-voltage backporch operation and a retrigger pulse generation; wherein the nonlinear inductor (27) has a nonlinearity to have a high inductance during any of the backporch operations and to have a low inductance during the turn-on pulse generation and retrigger pulse generation.

A power reception device 3 includes: an estimation circuit 28 estimating a load resistance of an entire contactless power feed apparatus 1; and a reception-side communicator 27 transmitting an estimated value of the load resistance of the entire contactless power feed apparatus 1 to a power transmission device 2. The power transmission device 2 has a power supply circuit 11 supplying AC power to a transmission coil 12 supplying power to the power reception device 3. The power transmission device 2 further includes a control circuit 18 decreasing an input/output gain of a transmission-side DC-DC converter 31 included in the power supply circuit 11 by a predetermined amount when the estimated value of the load resistance is less than a predetermined allowed lower limit, and maintaining or increasing the input/output gain when the estimated value of the load resistance is equal to or greater than the predetermined allowed lower limit.

A magnetic field for application to body tissue is generated via a first inductor. Connecting circuitry, including at least first and second branches, is provided between an electric storage device and the first inductor. A switch forming part of the first branch electrically connects the storage device to the first inductor enabling electrical current to flow through the first branch and the first inductor, thereby causing the first inductor to generate the field. The current flowing through the first branch represents a first direction of flow between the storage device and the first inductor. An electric component conducts current primarily in a forward direction. That component forms part of the second branch, enabling current to flow between the storage device and the first inductor through the second branch. The flow in the forward direction represents a second direction opposite the first. A second inductor is connected in series with the first inductor. The second inductor has a variable inductance or can be bypassed using bypass circuitry. Electrical current flowing through the first inductor and through the connecting circuitry will also flow through the second inductor or the bypass circuitry, regardless of whether the electrical current flows through the first or the second branch.

A magnetic field for application to body tissue is generated via a first inductor. Connecting circuitry, including at least first and second branches, is provided between an electric storage device and the first inductor. A switch forming part of the first branch electrically connects the storage device to the first inductor enabling electrical current to flow through the first branch and the first inductor, thereby causing the first inductor to generate the field. The current flowing through the first branch represents a first direction of flow between the storage device and the first inductor. An electric component conducts current primarily in a forward direction. That component forms part of the second branch, enabling current to flow between the storage device and the first inductor through the second branch. The flow in the forward direction represents a second direction opposite the first. A second inductor is connected in series with the first inductor. The second inductor has a variable inductance or can be bypassed using bypass circuitry. Electrical current flowing through the first inductor and through the connecting circuitry will also flow through the second inductor or the bypass circuitry, regardless of whether the electrical current flows through the first or the second branch.