This document describes the highly integrated ballast controller L6520 and L6521, which features a half bridge circuit capable of driving both BJT and MOSFET transistors, a very accurate oscillator with precision in a wide operating temperature range, BJT's storage time compensation, preheated start and instant start, hard switching protection, overcurrent/voltage protection, choke saturation control, and end-of-life protection. It is suitable for electronic ballasts and integrated CFLs applications.