For power levels below 100-150 watts, the most popular ballast topology comprises three key functional blocks:

a boost PFC stage to get sinusoidal input current and generate a stable DC bus voltage
a buck-converter to control lamp current and power
a half-bridge output stage to drive the lamp with low-frequency square waves

The state-of-art-solution is based on a two-stage architecture where a control unit manages both the lamp current and power and the driving stages. This allows the buck converter stage to be eliminated, making the solution cost effective without compromising the overall system performance. For every stage, ST offers a wide portfolio of ICs, discrete power components and reference board to speed up the design.