Patent ID: 7679293

Claim:
An electronic ballast for providing an asymmetric time-varying electrical output signal to drive at least one lamp, the electronic ballast comprising: an input circuit with first and second input terminals receiving an input from a power source, the input circuit including a first capacitor coupled between the first input terminal and an intermediate node, a second capacitor coupled between the intermediate node and the second input terminal, a first inductor coupled between the first input terminal and a first bus node, and a second inductor coupled between the second input terminal and a second bus node; a switching circuit operatively coupled between the bus nodes and an output terminal to selectively couple alternate ones of the bus nodes with the output node to create a time-varying output signal at the output node, the switching circuit including: a first switching device with a first switch terminal coupled with the first bus node, a second switch terminal coupled with the output terminal, and a control terminal actuated to render the first switching device conductive in one half-cycle of the switching circuit operation, and a second switching device with a first switch terminal coupled with the output terminal, a second switch terminal coupled with the second bus node, and a control terminal actuated to render the first switching device conductive in another half-cycle of the switching circuit operation; a resonant circuit including: a transformer primary winding coupled between the output terminal and the intermediate node, a resonant capacitor coupled in parallel with the transformer primary winding between the output terminal and the intermediate node, and an anti-striation circuit separate from the control terminals of the switching devices and coupled between the output terminal and at least one of the first bus terminal, the second bus terminal, and the intermediate node, the anti-striation circuit including at least one anti-striation component active to change a resonant frequency of the resonant circuit in a first portion of a resonant cycle and inactive in a second portion of the resonant cycle to cause the switching circuit to generate an asymmetric time-varying output signal at the output node; and an output circuit for outputting the asymmetric output signal to a lamp system.