1. Field of the Invention
This invention is directed to an electronic ballast system for fluorescent or gas discharge tubes. In particular, this invention relates to automatic gain control ballast systems for fluorescent tubes. More in particular, this invention relates to a ballast system which provides for frequency control mechanisms utilizing inductance characteristics of an inverter transformer to allow for a substantial frequency stabilization. Still further, this reference directs itself to a transistor switching mechanism which is feedback coupled to an induction circuit for establishing a regulated current for a gas discharge tube independent of the gain of a transistor used in a particular ballast system unit. Further, this invention directs itself to an electronic ballast system where there is provided a transistor switching network including a regulation control circuit for maintaining the power output of a gas discharge tube at a predetermined and substantially constant value. Still further, this invention relates to an electronic ballast system having a toroidal transformer to provide a predetermined variable inductance for regulating a power output to a gas discharge or fluorescent tube. Additionally, this invention pertains to an electronic ballast system which is transistorized and where the current gain of various transistors range over a wide value range from one system unit to another and provides for electrical circuitry which will maintain the gas discharge tube light output fluctuation to a minimum value.
2. Prior Art
Electronic ballast systems for gas discharge or fluorescent tubes are known in the art. However, in some prior art electronic ballast systems, no provision is made for frequency stabilization of the circuit. Thus, in such prior art electronic ballast system circuits, when a gas discharge tube is removed from the circuit, there is a deleterious flickering of the remaining gas discharge tubes, or in some cases, a complete breakdown of the visible light from the remaining gas discharge tubes.
In other prior art electronic ballast systems, the light output of the gas discharge tubes are highly dependent upon the gain of the transistors used in the circuits. In such prior art where the transistor gains between one unit and another vary over a great range, the light output from the gas discharge tube fluctuates by large amounts. In such prior art systems, additional circuitry must be added to such prior art electronic ballast systems to maintain the light output fluctuation as constant as possible between different units.
In the alternative, in such prior art electronic ballast systems, in order to maintain the light output fluctuation of the gas discharge tubes to a minimum value, the transistors used in the circuit must be matched within very restrictive ranges to obtain a substantially constant transistor gain from one unit to the next. Such procedures increase the cost of the electronic ballast systems, as well as providing for additional electronic elements, which increase both labor and capital investment in such electronic ballast systems.
By increasing the electrical components used in prior art electronic ballast systems to maintain the gas discharge tubes in operation, there is a responsive increase in the manufacturing costs of such prior art electronic ballast systems and a reduction in the reliability of these ballast systems.