Patent Application
20070013320
The present invention relates to a feedback circuit for push-pull inverters and particularly to a non-contact induction electric feedback device for a push-pull inverter which drives a discharge lamp by providing input electricity on two ends of the discharge lamp at a phase difference of 180 degrees that can regulate input electricity and maintain uniform luminance of the discharge lamp.
To improve illumination result and increase input electricity of discharge lamps, the driving method of using a push-pull inverter to ignite a discharge lamp by providing electricity at a phase difference of 180 degrees on two input electrodes at two ends of the discharge lamp has become an important technique. U.S. Pat. No. 6,087,757 discloses such a technique. It has a control unit to provide a driving frequency which alters input electricity to a transformer by 180 degrees of phase difference through a phase inversion circuit. U.S. Pat. No. 6,724,126 also discloses a technique which has a control unit to output frequencies of the same phase and two transformers of opposite polarity to generate input electricity at a phase difference of 180 degrees.
While the aforesaid patents have included discussion of the push-pull inverter, the two ends of the discharge lamp receive input electricity from the inverter. The discharge lamp cannot feed back the actual driving electricity condition through a coupling circuit to the control unit. In fact, after the discharge lamp has been used for a period of time, the discharge gas ages or input electrodes oxidize. As a result, the luminance of the discharge lamp becomes not uniform. If there is no feedback electricity sending timely to the control unit to adjust the driving frequency, aging of the discharge lamp will accelerate.
U.S. Pat. No. 6,087,757 provides a solution which connects the output side of the transformer to a lamp current detection device to get a feedback electricity detection value. It adopts a contact circuit which is not adaptable to the push-pull inverter.
The primary object of the present invention is to solve the aforesaid problems. The invention employs non-contact induction to get the detection electricity of the driving electricity of a discharge lamp. The detection electricity is transformed and feeds back to a control unit so that the frequency signal to maintain the required luminance of the discharge lamp can be adjusted instantly. As the invention uses non-contact coupling induction to get the detection electricity, any input electricity passing circuit may be employed in the circuit design. The invention is applicable to any type of push-pull inverters.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
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In the first embodiment, the first coil assembly 21 is located between the first transformer 13 and the discharge lamp 30. The second coil assembly 22 and the control unit 11 are interposed by a rectification element 23 and a filter element 24. When the driving electricity of the discharge lamp 30 passes through the first coil assembly 21, the second coil assembly 22 gets a detection electricity from external direct electromagnetic induction according to the coil ratio of the first coil assembly 21 and the second coil assembly 22. The detection electricity passes through the rectification element 23 and the filter element 24 to be rectified and filtered, and inputs to the control unit 11. The control unit 11, according to the driving electricity of the discharge lamp 30 for generating the required luminance, outputs a duty frequency to the first transformer 13 and the second transformer 14 to determine the voltage boosting ratio. Thereby a uniform luminance and stable regulation can be achieved for the discharge lamp 30.
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While the preferred embodiments of the invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.
