Electronic ballast for multiple LED lamps with independent brightness control

Light-emitting-diode (LED) light sources, which are more compact, capable to change color in real time, less dissipative and more durable, are finding more applications in domestic, commercial and industrial environments. However, requirements such as high power factor, long lifetime, accurate current control and high efficiency pose challenges to the design of LED ballast circuits. This paper proposes an LED ballast with a first-stage isolated current-fed power factor correction (PFC) pre-regulator that puts the short-lifetime high-voltage storage capacitor to the secondary, thus extending the overall system lifetime. Furthermore, the high voltage stress on the main switch, which is typical in current-fed converters, is reduced substantially by appropriately exploiting the transformer leakage inductance. The design uses two secondary transformer windings and an LED current driver to form a non-cascading structure to improve efficiency. Multiple non-cascading structures can be used for LED lamps for instant independent brightness control. Analysis, design example and prototype verification are given for the LED ballast.