The problem of electronic ballast needing to be shut down has been addressed in the prior art. For example, in U.S. Pat. No. 5,744,912 to So, issued Apr. 28, 1998 entitled Electronic Ballast Having An Oscillator Shutdown Circuit For Single Or Multiple Fluorescent Tubes For Lamps provides for a relay which disables the ballast by shutting down the power supply. The abstract of So discloses generally, “An electronic ballast having particular application for driving small diameter fluorescent tubes or lamps (such as the T2, T4 and T5 sizes). The electronic ballast has a shutdown circuit by which to remove power to the oscillator when the tube or lamp is close to the end of its useful life or when an abnormal condition occurs such that a rise in operating voltage is detected. The shutdown circuit detects the rise in the operating voltage of the tube or lamp and energizes a relay through the conduction path of a photoresponsive transistor that is rendered conducting by a light emitting diode. The relay directs power away from the oscillator and towards the control electrode of the photoresponsive transistor to hold the phototransistor on and thereby disable the ballast. The ballast also includes a power factor controller to provide a high power factor and a more efficient operation.” The So patent is hereby incorporated by reference. Besides the method described in the So patent, there are probably a wide variety of other methods for shutting down a ballast oscillator when a tube or lamp is nearing the end of its life.
The present invention uses the method of deactivating transformer winding which would demagnetize the transformer to stop oscillation and shut down the circuitry without shutting down the entire ballast.
As an alternate embodiment, shown in
The circuitry in
When the lamp is deactivated or reaches end of life, there would be a high voltage on sample point 8 by the lamp. This voltage is sampled through C9 and R6, then rectified by D11. The rectified voltage charges C10 to voltage that passes the threshold of zener diode D5 and triggers Q3. R7 will keep Q3 in the on state. T1-1 will get shortened through D5 and Q3 and de-magnetizing the transformer. The oscillation will stop and circuitry goes to shutdown mode.
Thus, the protection circuitry stops oscillation by demagnetizing a winding of the transformer when there is abnormal voltage to the lamp. The protection means thus deactivates the oscillation means when the output means outputs an abnormally high voltage.
Number | Name | Date | Kind |
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20040222752 | Yamanaka et al. | Nov 2004 | A1 |
20080278088 | Yu et al. | Nov 2008 | A1 |
Number | Date | Country | |
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20100259173 A1 | Oct 2010 | US |