EVAL6569: 18W CFL Lamp, 120 / 230 VAC

A demonstration board was developed as an example for Compact Fluorescent Lamp ballast. It is optimised for a CF18DT/E/830 18W lamp from Osram-Sylvania. Using the L6569 the circuit achieves preheat, ignition and normal lamp operation. The power transistors are two STD3NA50 500V-3W MOSFETs in I-PACK package.

The three sections of the board are an AC input rectifier, the half bridge inverter, and the resonant ballast. By changing the connection on the input mains, the ballast can operate either on 120 Vac mains with a voltage doubler rectification, or on 230 Vac mains with a full wave rectification. The input resistor R1 limits the initial inrush current charging the bulk capacitors.

The L6569 operates with a single 50 kHz switching frequency programmed by R4 and C1. Two fast diodes D2 & D3 synchronize the oscillator to keep the switching in ZVS mode. The control circuit requires 4.5 mA to supply the IC, the MOS gate drives, and the oscillator. Its supply delivers at least 6.5 mA as described in appendix B. The start up resistor also balances the voltage across the two bulk capacitors.