Inductively coupled ballast circuit
A ballast circuit is disclosed for inductively providing power to a load. The ballast circuit includes an oscillator, a driver, a switching circuit, a resonant tank circuit and a current sensing circuit. The current sensing circuit provides a current feedback signal to the oscillator that is representative of the current in the resonant tank circuit. The current feedback signal drives the frequency of the ballast circuit causing the ballast circuit to seek resonance. The ballast circuit preferably includes a current limit circuit that is inductively coupled to the resonant tank circuit. The current limit circuit disables the ballast circuit when the current in the ballast circuit exceeds a predetermined threshold or falls outside a predetermined range.
1. A non-contact power transfer system comprising:
a non-contact power supply including:
a primary subcircuit having a primary;
a sensor configured to sense a characteristic of power that changes over time, said sensor configured to provide a first sensor output indicative of said characteristic of power at a first time, said sensor configured to provide a second sensor output indicative of said characteristic of power at a second time different from said first time;
a control circuit supplying power to said primary, said control circuit making an adjustment of an operational characteristic of said non-contact power supply based on both said first sensor output and said second sensor output;
an electronic device separable from said non-contact power supply, said electronic device being absent from physical interconnection with said non-contact power supply and absent from electrical connection with said non-contact power supply, said electronic device and said non-contact power supply capable of inductively coupling when in sufficient proximity to each other said electronic device includes:
a secondary for inductively coupling with said primary, said secondary being absent from physical interconnection with said primary, said secondary being absent from electrical connection with said primary, wherein said primary is capable of inductively energizing said secondary; and
a load electrically connected to said secondary, whereby power is provided to said load by said secondary;
whereby said electronic device is readily placeable in sufficient proximity to said non-contact power supply to inductively receive power without the need to make electrical connection with said non-contact power supply and without the need to make physical interconnection with said non-contact power supply; and
whereby said electronic device is readily removable from the sufficient proximity of said non-contact power supply without the need to disconnect electrical connection with said non-contact power supply and without the need to disconnect physical interconnection with said non-contact power supply.
2. The non-contact power transfer system of claim 1 wherein said sensor senses said characteristic of power in said primary subcircuit.
3. The non-contact power transfer system of claim 1 wherein said operational characteristic is an operating frequency of said primary subcircuit.
4. The non-contact power transfer system of claim 1 wherein said sensor is a current sensor, and wherein said characteristic of power sensed by said sensor is a current of power in said primary subcircuit.
5. The non-contact power transfer system of claim 4 wherein said first sensor output is indicative of said current of power at said first time, wherein said second sensor output is indicative of said current of said power at said second time, and wherein said adjustment is proportional to a change in current over time from said first sensor output to said second sensor output.
6. The non-contact power transfer system of claim 4 wherein said control circuit includes an operational amplifier operably coupled to said current sensor and a buffer circuit, wherein an output of said operational amplifier is electrically coupled to a driver circuit through said buffer circuit, and wherein said driver circuit is configured to control supply of power to the primary subcircuit based on said output of said operational amplifier.
7. The non-contact power transfer system of claim 6 wherein said output of said operational amplifier at said first time is based on said first sensor output, wherein said output of said operational amplifier is operably coupled to a negative lead of said operational amplifier.
8. The non-contact power transfer system of claim 7 wherein, at said second time, said second sensor output is operably coupled to a positive lead of said operational amplifier, wherein said operational amplifier makes an adjustment to said output based on a difference between a signal on said positive lead and a signal on said negative lead.
9. The non-contact power transfer system of claim 1 wherein said control circuit is configured to make a plurality of adjustments of said operational characteristic over time, wherein each of said plurality of adjustments is based on at least two sensor outputs obtained from said sensor at different points in time.
10. The non-contact power transfer system of claim 1 wherein said load is further defined as a resonant lamp circuit.
11. The non-contact power transfer system of claim 1 wherein said primary is disposed in a series resonant tank circuit.
12. The non-contact power transfer system of claim 1 wherein said load includes an electromagnetic radiation emitting device.
13. The non-contact power transfer system of claim 1 wherein said load is one of an ultraviolet lamp, an incandescent lamp, a light emitting diode lamp, a pulsed white light lamp and a dielectric barrier discharge lamp.
14. The non-contact power transfer system of claim 1 wherein an amplitude of said characteristic of power varies as a function of changes in said load.
15. The non-contact power transfer system of claim 14 wherein changes in said load include at least one of installation of said load, removal of said load, positional changes of said load with respect to said non-contact power supply, changes in impedance of said load, changes in temperature of said load, and changes in impedance over the life of said load.
16. The non-contact power transfer system of claim 1 wherein said control circuit is configured to make said adjustment based on a single type of sensor output.
17. The non-contact power transfer system of claim 16 wherein said single type of sensor output is a current in said primary.
18. A method for supplying power from a wireless power supply to an electronic device through an inductive coupling, comprising the steps of:
removably placing at least one of a secondary of the electronic device and a primary of the wireless power supply into sufficient proximity of the other absent of physical interconnection between the electronic device and the wireless power supply and absent of electrical connection between the electronic device and the wireless power supply;
supplying a power at a frequency to the primary to transfer power across an inductive coupling between the primary and the secondary absent of physical interconnection between the primary and the secondary, and absent of electrical connection between the primary and the secondary;
generating power within the secondary across the inductive coupling, the generated power being applied to the load of the electronic device;
sensing a characteristic of power in the wireless power supply at a first time to generate a first sensor output, the sensed characteristic of power being affected by a characteristic of the load reflected through the inductive coupling;
sensing the characteristic of power in the wireless power supply at a second time different from the first time to generate a second sensor output;
making an adjustment to an operational characteristic of the power supplied to the primary based on both the first sensor output and the second sensor output;
whereby the electronic device is readily placeable in sufficient proximity to the non-contact power supply to inductively receive power without the need to make electrical connection with the non-contact power supply and without the need to make physical interconnection with the non-contact power supply; and
whereby the electronic device is readily removable from the sufficient proximity of the non-contact power supply without the need to disconnect electrical connection with the non-contact power supply and without the need to disconnect physical interconnection with the non-contact power supply.
19. The method of claim 18 wherein the characteristic of the power includes current in the primary.
20. The method of claim 18 wherein the operational characteristic of power includes said frequency of said power supplied to said primary.
21. An inductive power supply for supplying power inductively to an electronic device separable from the inductive power supply, the inductive power supply comprising:
a primary circuit including a primary configured to inductively couple with a secondary of the electronic device to transfer power to the electronic device without a physical connection with electronic device and without an electrical connection with the electronic device, wherein said primary is capable of inductively coupling with the electronic device when in sufficient proximity to the electronic device;
a sensor configured to sense a characteristic of power in the inductive power supply that changes over time, said sensor configured to provide a first sensor output indicative of said characteristic of power at a first time, said sensor configured to provide a second sensor output indicative of said characteristic of power at a second time different from said first time;
a control circuit for supplying power to said primary, said control circuit configured to make an adjustment of an operational characteristic of the inductive power supply based on both said first sensor output and said second sensor output;
whereby the electronic device is readily placeable in sufficient proximity to said primary circuit to inductively receive power without the need to make electrical connection with said primary circuit and without the need to make physical interconnection with said primary circuit; and
whereby the electronic is readily removable from the sufficient proximity of said primary circuit without the need to disconnect electrical connection with said primary circuit and without the need to disconnect physical interconnection with said primary circuit.
22. The inductive power supply of claim 21 wherein said sensor senses said characteristic of power in said primary circuit.
23. The inductive power supply of claim 22 wherein said sensor is a current sensor, and wherein said characteristic of power sensed by said sensor is a current of power in said primary subcircuit.
24. The inductive power supply of claim 23 wherein said first sensor output is indicative of said current of power at said first time, and wherein said second sensor output is indicative of said current of said power at said second time, and wherein said adjustment is proportional to a change in current over time from said first sensor output to said second sensor output.
25. The non-contact power transfer system of claim 23 wherein said control circuit is configured to make said adjustment based on a single type of sensor output, wherein both said first sensor output and said second sensor output are said single type of sensor output.
26. The non-contact power transfer system of claim 25 wherein said single type of sensor output is a current in said primary.
27. The inductive power supply of claim 21 wherein said control circuit is configured to make a plurality of adjustments of said operational characteristic over time, wherein each of said plurality of adjustments is based on at least two sensor outputs obtained from said sensor at different points in time.
28. The inductive power supply of claim 21 wherein said operational characteristic is an operating frequency of said primary circuit.
29. The inductive power supply of claim 21 wherein said first and second sensor outputs are indicative of an amplitude of said characteristic of power.