Transformer-isolated power transfer apparatus having intermittent and continuous oscillation modes of operation

• US 5,898,578 A
• Filed: 12/23/1997
• Issued: 04/27/1999
• Est. Priority Date: 12/24/1996
• Status: Expired due to Term

• Current Assignee: Panasonic Electric Works Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Asahi Matsushita Electric Works Ltd. (Panasonic Holdings Corporation)
• Inventors: Tamura, Hideki, Katsura, Yoshiki, Yamashita, Mikihiro
• Primary Examiner(s): Riley, Shawn
• Application Number:
  US08/996,511
• Time in Patent Office: 490 Days
• Field of Search: 363/19, 363/18
• US Class Current: 363/19
• CPC Class Codes: H01F 38/14 Inductive couplings for wireless supply or distribution of electric power using inductive coupling H02J50/10
• 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

Abstract

A transformer-isolated power transfer apparatus included in a power supply body and a device body that are removably coupled together. The power supply body contains a primary winding and a secondary winding for transmitting electrical power. The device body contains an induction winding and a load. When the power supply body and device body are coupled together, the secondary winding in the power supply body is electromagnetically inductively coupled to the induction winding provided in the device body to transfer power from the power supply body to the device body via electromagnetic inductive coupling. The apparatus further includes detection circuitry that detects when the power supply body and the device body are coupled together. The power supply body further contains an oscillation drive circuit that drives the primary winding in the power supply body in an intermittent oscillation mode of operation when the detection circuitry detects that the power supply body is not coupled to the device body, and that drives the primary winding in the power supply body in a continuous oscillation mode of operation when the detection circuitry detects that the power supply body is coupled to the device body. During the intermittent oscillation mode of operation, the oscillation on period is controllably varied in response to variations in an input voltage in a manner such as to maintain an average power transmitted from the power supply body to the device body at a substantially constant level. In this manner, the detection circuitry can reliably detect when the power supply body and the device body are coupled together despite variations in the input voltage.

Claims

1. A transformer-isolated power transfer apparatus, comprising:

a primary winding wound around a core;

a first transistor coupled between an oscillation drive circuit and the primary winding, the first transistor having a control electrode;

a secondary winding wound around the core, wherein the primary winding is driven in oscillation in response to the first transistor being turned on, to thereby induce the secondary winding to produce an output voltage;

a rectifier coupled to the output voltage for rectifying the output voltage, to thereby produce a rectified output voltage;

a time delay circuit coupled to the rectified output voltage for producing an oscillation control voltage after a variable time delay period which is inversely proportional to the magnitude of the rectified output voltage;

a second transistor coupled between the control electrode of the first transistor and the secondary winding, the second transistor having a control electrode coupled to the oscillation control voltage, wherein the second transistor is turned on when the oscillation control voltage reaches a prescribed threshold value, and is turned off when the oscillation control voltage falls below the prescribed threshold value;

wherein the first transistor is turned on in response to the second transistor being turned off, and the first transistor is turned off in response to the second transistor being turned on, whereby the primary winding is driven in oscillation intermittently at intervals having a duration inversely proportional to the magnitude of the output voltage.

2. The transformer-isolated power transfer apparatus as set forth in claim 1, wherein the primary winding, the secondary winding, the rectifier, the time delay circuit, and the first and second transistors are contained within a power supply body.

3. The transformer-isolated power transfer apparatus as set forth in claim 2, further comprising a device body coupled to the power supply body.

4. The transformer-isolated power transfer apparatus as set forth in claim 3, wherein power produced by the primary winding is transferred to a device body.

5. The transformer-isolated power transfer apparatus as set forth in claim 4, wherein the average power produced by the primary winding is substantially constant, regardless of variations in the magnitude of an input voltage applied to the power supply body.

6. The transformer-isolated power transfer apparatus as set forth in claim 3, wherein the primary winding produces an intermittent detection signal.

7. The transformer-isolated power transfer apparatus as set forth in claim 6, wherein:

the device body includes a signal detection circuit which produces a response signal responsive to detection of the intermittent detection signal;

the power supply body includes a response signal reception circuit which receives the response signal produced by the device body, and in response thereto produces a power supply control signal;

the power supply body further includes a third transistor connected between the control electrode of the second transistor and a reference node, the third transistor having a control electrode coupled to the power supply control signal; and

,

wherein the third transistor is turned on in response to the power supply control signal, and the second transistor is turned off in response to the third transistor being turned on, whereby the first transistor is turned on, to thereby drive the primary winding in oscillation.

8. The transformer-isolated power transfer apparatus as set forth in claim 6, wherein:

the device body includes a signal detection circuit which produces a response signal responsive to detection of the intermittent detection signal;

the power supply body includes a response signal reception circuit which receives the response signal produced by the device body, and in response thereto produces a power supply control signal;

the power supply body further includes a third transistor connected between the control electrode of the second transistor and a reference node, the third transistor having a control electrode coupled to the power supply control signal; and

wherein the third transistor is turned on in response to the power supply control signal, and the second transistor is turned off in response to the third transistor being turned on, whereby the first transistor is turned on, to thereby drive the primary winding in continuous oscillation.

9. The transformer-isolated power transfer apparatus as set forth in claim 7, wherein the intermittent detection signal has a substantially constant average power, whereby a voltage level induced in the signal detection circuit is substantially constant, to thereby enable reliable detection of the intermittent detection signal using a fixed threshold voltage value, regardless of variations in the magnitude of an input voltage applied to the power supply body.

10. The transformer-isolated power transfer apparatus as set forth in claim 8, wherein the intermittent detection signal has a substantially constant average power, whereby a voltage level induced in the signal detection circuit is substantially constant, to thereby enable reliable detection of the intermittent detection signal using a fixed threshold voltage value, regardless of variations in the magnitude of an input voltage applied to the power supply body.

11. The transformer-isolated power transfer apparatus as set forth in claim 1, wherein the time delay circuit comprises an RC circuit.

12. A transformer-isolated power transfer apparatus, comprising:

an oscillation circuit having an oscillation on mode for producing an electromagnetic signal, and an oscillation off mode;

an intermittent drive circuit coupled to the oscillation circuit for receiving the electromagnetic signal and for generating a first control signal having a first logic level which has a duration which is inversely proportional to a magnitude of the electromagnetic signal, and a second logic level; and

,

a control device responsive to the first control signal for placing the oscillation circuit in the oscillation on mode in response to the first control signal having the first logic level, and for placing the oscillation circuit in the oscillation off mode in response to the first control signal having the second logic level.

13. The transformer-isolated power transfer apparatus as set forth in claim 12, further comprising a power supply body for housing the oscillation circuit, the intermittent drive circuit, and the control device.

14. The transformer-isolated power transfer apparatus as set forth in claim 13, wherein the oscillation circuit produces an intermittent detection signal at intervals corresponding to the oscillation on mode, and further comprising a device body which includes a signal detection circuit which produces a response signal responsive to detection of the intermittent detection signal.

15. The transformer-isolated power transfer apparatus as set forth in claim 14, further comprising:

a response signal detection circuit which receives the response signal produced by the device body, and in response thereto produces a second control signal; and

,

wherein the control device is responsive to the second control signal for placing the oscillation circuit in a continuous oscillation mode.

16. A transformer-isolated power transfer apparatus, comprising:

oscillation means having an oscillation on mode for producing an electromagnetic signal, and an oscillation off mode;

intermittent drive means coupled to the oscillation means for receiving the electromagnetic signal and for generating a control signal having a first logic level which has a duration which is inversely proportional to a magnitude of the electromagnetic signal, and a second logic level; and

, control means responsive to the control signal for placing the oscillation means in the oscillation on mode in response to the first control signal having the first logic level, and for placing the oscillation means in the oscillation off mode in response to the control signal having the second logic level.

17. A transformer-isolated power transfer apparatus included in a power supply body and a device body that are removably coupled together, wherein the power transfer apparatus includes:

an electromagnetic power supply means contained in the power supply body;

an induction winding and load contained in the device body, wherein when the power supply body and the device body are coupled together, the electromagnetic power supply means in the power supply body is electromagnetically inductively coupled to the induction winding in the device body to transfer power from the power supply body to the device body via electromagnetic inductive coupling;

detection circuitry for detecting when the power supply body and the device body are coupled together;

an oscillation drive circuit that drives the electromagnetic power supply means in a continuous oscillation mode of operation in response to the detection circuitry detecting that the power supply body and the device body are coupled together, and that drives the electromagnetic power supply means in an intermittent oscillation mode of operation when the power supply body and the device body are not coupled together; and

,

wherein, in the intermittent oscillation mode of operation, the oscillation drive circuit controllably varies an oscillation on period in response to variations in an input voltage in a manner such as to maintain an average level of the power transmitted from the power supply body to the device body at a substantially constant level.

18. The power transfer apparatus as set forth in claim 17, wherein the electromagnetic power supply means includes a primary winding and the oscillation drive circuit includes a secondary winding.

19. The power transfer apparatus as set forth in claim 17, wherein the detection circuitry includes:

a response signal generating circuit contained in the device body for generating a response signal upon detecting a threshold value of the power transmitted by the electromagnetic power supply means when the power supply body and the device body are coupled together;

a response signal receiving circuit contained in the power supply body for receiving the response signal generated by the response signal generating circuit and for generating an oscillation mode switching signal in response to receiving the response signal; and

,

wherein the oscillation drive circuit is responsive to the oscillation mode switching signal to change the oscillation mode of operation from the intermittent oscillation mode of operation to the continuous oscillation mode of operation.

20. A transformer-isolated power transfer apparatus according to claim 17, wherein the oscillation drive circuit includes:

a control transistor coupled to the electromagnetic power supply means for controlling the oscillation on period during the intermittent oscillation mode of operation;

a capacitor that is coupled to the control transistor and that is charged to a predetermined voltage level during a predetermined period of oscillation; and

,

wherein the control transistor is turned on in response to the capacitor being charged to the predetermined voltage level, and is turned off during the predetermined period of oscillation.

21. The power transfer apparatus as set forth in claim 19, wherein the oscillation drive circuit includes:

a control transistor coupled to the electromagnetic power supply means for controlling the oscillation on period during the intermittent oscillation mode of operation;

a capacitor that is coupled to the control transistor and that is charged to a predetermined voltage level during a predetermined period of oscillation; and

,

wherein the control transistor is turned on in response to the capacitor being charged to the predetermined voltage level, and is turned off during the predetermined period of oscillation.

22. The power transfer apparatus as set forth in claim 19, further including a switching transistor coupled to the control transistor, wherein the switching transistor turns off the control transistor to terminate the intermittent oscillation mode of operation in response to the oscillation mode switching signal.

23. The power transfer apparatus as set forth in claim 21, further including a switching transistor coupled to the control transistor, wherein the switching transistor turns off the control transistor to terminate the intermittent oscillation mode of operation in response to the oscillation mode switching signal.

24. A transformer-isolated power transfer apparatus included in a power supply body and a device body that are removably coupled together, wherein the power transfer apparatus includes:

an electromagnetic power supply means contained in the power supply body;

an induction winding and load contained in the device body, wherein when the power supply body and the device body are coupled together, the electromagnetic power supply means in the power supply body is electromagnetically inductively coupled to the induction winding in the device body to transfer power from the power supply body to the device body via electromagnetic inductive coupling;

detection circuitry for detecting when the power supply body and the device body are coupled together;

an oscillation drive circuit that drives the electromagnetic power supply means in a continuous oscillation mode of operation in response to the detection circuitry detecting that the power supply body and the device body are coupled together, and that drives the electromagnetic power supply means in an intermittent oscillation mode of operation when the power supply body and the device body are not coupled together; and

,

wherein the oscillation drive circuit includes;

a control transistor coupled to the electromagnetic power supply means for controlling the oscillation on period during the intermittent oscillation mode of operation;

a capacitor that is coupled to the control transistor and that is charged to a predetermined voltage level during a predetermined period of oscillation; and

,

wherein the control transistor is turned on in response to the capacitor being charged to the predetermined voltage level, and is turned off during the predetermined period of oscillation.