Piezoelectrically actuated variable capacitor
First Claim
1. A ballast for an electrodeless high intensity discharge lamp of the type having an excitation coil situated about an arc tube for exciting an arc discharge therein upon application of a radio frequency signal to said excitation coil, said ballast comprising:
- first and second switching devices connected in series in a half-bridge configuration with a junction therebetween;
ballast drive means coupled to said first and second switching devices, said ballast drive means being adapted to be coupled to an RF power supply for alternately driving said first and second switching devices;
resonant circuit means coupled to said first and second switching devices at the junction therebetween, said resonant circuit means comprising said excitation coil, a parallel capacitor in parallel combination with said excitation coil, and a series capacitor coupled in series with said parallel combination, said parallel and series capacitors each comprising first and second conductive plates with a dielectric disposed therebetween, said second conductive plate of said series capacitor being separated by a first predetermined distance from said first conductive plate thereof during initiation of the arc discharge so that the ballast is in tune under lamp-starting conditions; and
piezoelectric actuating means for moving at least a portion of said second conductive plate of said series capacitor with respect to said first conductive plate thereof, after initiation of the arc discharge, in response to a control voltage, so that the ballast is in tune under lamp-running conditions.
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Accused Products
Abstract
A variable capacitor includes a fixed conductive plate and a movable conductive plate with a dielectric disposed between them. A piezoelectric actuator is used to vary the distance between the conductive plates by moving the movable plate with respect to the fixed plate, with capacitance changing in inverse proportion to distance moved. In an electrodeless high intensity discharge lamp ballast, such a variable capacitor is situated in series with the excitation coil of the lamp. When a control voltage is applied to the piezoelectric actuator, the movable plate is moved from a starting position to a running position so as to maintain the ballast load in tune under both starting and running conditions, respectively, resulting in higher efficiency operation.
48 Citations
20 Claims
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1. A ballast for an electrodeless high intensity discharge lamp of the type having an excitation coil situated about an arc tube for exciting an arc discharge therein upon application of a radio frequency signal to said excitation coil, said ballast comprising:
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first and second switching devices connected in series in a half-bridge configuration with a junction therebetween; ballast drive means coupled to said first and second switching devices, said ballast drive means being adapted to be coupled to an RF power supply for alternately driving said first and second switching devices; resonant circuit means coupled to said first and second switching devices at the junction therebetween, said resonant circuit means comprising said excitation coil, a parallel capacitor in parallel combination with said excitation coil, and a series capacitor coupled in series with said parallel combination, said parallel and series capacitors each comprising first and second conductive plates with a dielectric disposed therebetween, said second conductive plate of said series capacitor being separated by a first predetermined distance from said first conductive plate thereof during initiation of the arc discharge so that the ballast is in tune under lamp-starting conditions; and piezoelectric actuating means for moving at least a portion of said second conductive plate of said series capacitor with respect to said first conductive plate thereof, after initiation of the arc discharge, in response to a control voltage, so that the ballast is in tune under lamp-running conditions. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An electrodeless high intensity discharge lamp system, comprising:
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an electrodeless high intensity discharge lamp including an excitation coil situated about an arc tube which contains a fill; a ballast for providing a first radio frequency signal to said excitation coil for exciting an arc discharge in said arc tube, said ballast including first and second switching devices connected in series in a high-bridge configuration with a junction therebetween, said ballast further including resonant circuit means coupled to said first and second switching devices at the junction. therebetween, said resonant circuit means encompassing said excitation coil and further including a parallel capacitor in parallel combination with said excitation coil, and a series capacitor coupled in series with said parallel combination, said parallel and series capacitors each comprising first and second conductive plates with a dielectric therebetween, said second conductive plate of said series capacitor being separated by a first predetermined distance from said first conductive plate thereof so that the ballast is in tune under lamp-starting conditions; first piezoelectric actuating means for moving at least a portion of said second conductive plate of said series capacitor with respect to said first conductive plate thereof in response to a control voltage so that the ballast is in tune under lamp-running conditions; and at least one starting electrode disposed proximate said arc tube at least during initiation of the arc discharge therein. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification