Electronic ballast with feed-forward control

Abstract

An electronic ballast is provided which is capable of compactly powering a discharge lamp from a source of rectified, but unregulated, power having a varying DC voltage. The ballast includes a self-oscillating converter powered by the DC voltage for producing pulses at a nominal operating frequency which is determined by a resonant tank. The resonant tank converts the pulses to a sinusoidal current for powering the discharge lamp and includes an inductive impedance in series with the lamp for providing a voltage drop which varies with the operating frequency. A feed-forward control circuit is coupled to the converter for varying the operating frequency directly with variations in the DC source voltage. The voltage drop across the inductive impedance is substantially proportional to the magnitude of the DC source voltage. This enables regulation of the voltage supplied to the discharge lamp by the ballast without sensing the lamp voltage itself.

Description

[0001] 1. Field of the Invention[0002] This invention relates to electronic ballasts for discharge lamps such as fluorescent lamps and, in particular, to such ballasts which are useful in applications where compact size is desirable.[0003] 2. Description of Related Art[0004] There is an ever-increasing demand for smaller electronic ballasts. In order to achieve this goal, a variety of problems must be overcome, for example:[0005] If the operating frequency of ballast circuitry is increased sufficiently to achieve a substantial reduction in the sizes of magnetic and filtering elements, power losses tend to increase.[0006] Decreasing the size of filtering components tends to have a negative impact on circuit performance.[0007] It is an object of the invention to provide an electronic ballast for discharge lamps which can be made compact without substantially increasing cost or adversely affecting performance.[0008] In accordance with the invention, an electronic ballast includes a sou...

AI Technical Summary

Benefits of technology

[0009] Such a ballast does not require a regulated DC power supply and will operate effectively with a filter capacitor that is much reduced in size from capacitors that are typically used to reduce ripple of the rectified DC power.

Problems solved by technology

If the operating frequency of ballast circuitry is increased sufficiently to achieve a substantial reduction in the sizes of magnetic and filtering elements, power losses tend to increase.

Decreasing the size of filtering components tends to have a negative impact on circuit performance.

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