Anti-arcing protection circuit for an electronic ballast

#A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

#The present invention relates generally to circuitry for instant-start gas-discharge lamp ballasts. More particularly, the present invention relates to circuitry designed to overcome arcing problems associated with current-fed, parallel-resonant inverter topologies used in electronic ballasts.

#The instant-start type of fluorescent lamp ballast has the advantage of fast starting. It is cost-effective and is particularly appropriate for long, continuous operation. A current-fed parallel-resonant inverter topology is known in the art as a particularly good solution for this kind of instant start application.

#FIG. 1 is a schematic of a typical circuit topology for dual-lamp current-fed parallel-resonant circuit of the prior art.

#FIG. 2 is a schematic of a lamp current rate of change sensing circuit of an embodiment of the present invention coupled with the load circuit of FIG. 1.

#FIG. 3 is a schematic of an arc protection circuit of the present invention showing an embodiment of a startup delay circuit.

#Throughout the specification and claims, the following terms take at least the meanings explicitly associated herein, unless the context dictates otherwise. The meanings identified below do not necessarily limit the terms, but merely provide illustrative examples for the terms. The meaning of “a,” “an,” and “the” may include plural references, and the meaning of “in” may include “in” and “on.” The phrase “in one embodiment,” as used herein may or may not refer to the same embodiment. The term “coupled” means at least either a direct electrical connection between the connected items or an indirect connection through one or more passive or active intermediary devices. The term “circuit” means at least either a single component or a multiplicity of components, either active and/or passive, that are coupled together to provide a desired function. The term “signal” means at least one current, voltage, charge, temperature, data or other signal. Where either a field effect transistor (FET) or a bipolar junction transistor (BJT) may be employed as an embodiment of a transistor, the scope of the terms “gate,” “drain,” and “source” includes “base,” “collector,” and “emitter,” respectively, and vice-versa. The term “load” means one or more gas discharge lamps, electrical components, and/or any other devices that consume electric power during normal operation.

#Referring generally to FIGS. 1-7 and the following detailed description, various embodiments of an arc protection circuit 10 are provided for an instant-start type electronic ballast having, for example, a current-fed, parallel resonant inverter capable of powering a load, such as one or more gas discharge lamps. The protection circuit 10 is capable of measuring a current across the load and detecting a disturbance such as an arc having a rate of change substantially in excess of normal operation. The circuit 10 is further capable of shutting down the ballast in response to the detected disturbance.

#The circuit 10 is configured to prevent shutdown of the ballast during a predetermined time period defined by associated circuitry. The predetermined time period is preferably sufficient to permit normal startup of the ballast and lamp ignition but short enough to efficiently disable the ballast in response to a true and potentially damaging arc. In this way the ballast is protected from undesirable shutdowns that might result from transient signals common during, for example, startup or re-lamping conditions.