CONTACTLESS POWER TRANSMISSION CIRCUIT

• US 20100171367A1
• Filed: 12/08/2009
• Published: 07/08/2010
• Est. Priority Date: 01/08/2009
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Electric Works Company Limited (Panasonic Holdings Corporation)
• Inventors: KADA, Kyohei, KITAMURA, Hiroyasu
• Granted Patent: US 8,319,376 B2
• Time in Patent Office: Days
• US Class Current: 307/104
• CPC Class Codes: H02J 50/10 using inductive coupling
• CPC Class Codes: H02J 50/12 of the resonant type
• CPC Class Codes: H02J 50/90 involving detection or optimisation of position, e.g. alignment
• CPC Class Codes: H02J 7/00712 the cycle being controlled or terminated in response to electric parameters
• CPC Class Codes: H02M 3/3385 with automatic control of output voltage or current H02M3/33561 takes precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A driving circuit drives a switching element such that an ON-period of the switching element is shorter when a power receiving device is detected not to be placed than when the power receiving device is placed.

Claims

1. A contactless power transmission circuit for transmitting power in a contactless state to a power receiving device placed on a placing portion, comprising:

a resonant circuit including a power transmission coil for transmitting power to the power receiving device and a resonant capacitor which resonates with the power transmission coil;

a switching element for resonating the resonant circuit by being repeatedly turned on and off; and

a driving circuit for detecting whether or not the power receiving device is placed on the placing portion based on a voltage of the power transmission coil and driving the switching element such that an ON-period of the switching element is shorter when the power receiving device is detected not to be placed than when the power receiving device is placed.

2. A contactless power transmission circuit according to claim 1, wherein the driving circuit includes:

a self-oscillating circuit for repeatedly turning the switching element on and off based on the voltage of the power transmission coil and causing the self-oscillation of the resonant circuit; and

an intermittent driving circuit for intermittently driving the self-oscillating circuit when the power receiving device is detected not to be placed.

3. A contactless power transmission circuit according to claim 1, wherein the driving circuit causes the separately-excited oscillation of the resonant circuit by outputting a PWM signal to the switching element and sets a lower duty ratio of the PWM signal when the power receiving device is detected not to be placed than when the power receiving device is placed.

4. A contactless power transmission circuit according to claim 2, wherein the intermittent driving circuit includes:

a first transistor connected to a control terminal of the switching element for turning the switching element off;

a voltage dividing resistor for dividing a voltage of the resonant circuit and outputting the divided voltage to a control terminal of the first transistor;

a diode connected between the resonant circuit and the voltage dividing resistor; and

a first capacitor connected to the control terminal of the first transistor and charged with the voltage divided by the voltage driving resistor.

5. A contactless power transmission circuit according to claim 4, wherein the intermittent driving circuit includes a voltage regulator diode connected between the diode and the voltage dividing resistor.

6. A contactless power transmission circuit according to claim 4, wherein:

the self-oscillating circuit includes a second transistor for turning the switching element off and a second capacitor connected to a control terminal of the second transistor;

the second transistor is commonly used as the first transistor; and

the second capacitor is commonly used as the first capacitor.