Abstract: The electronic HID ballast includes a Pulse-Phase-Modulation (PPM) pulse source, a switch driver, a power switching circuit, a coupling circuit, a DC starter, a switch current amplitude feedback circuit and a switch current pulse width feedback circuit. The PPM pulse source works at PPM mode with a fixed frequency to prevent acoustic arc resonance, and uses pulse deduction method to protect the ballast from overload during the starting period. The PPM pulse source, the switch driver, the switch current amplitude feedback circuit and the power switching circuit work together, functioning as a constant power switching source to energize lamp through the coupling circuit. The power switching circuit and the lamp are in DC series connection for the open load protection. The coupling circuit uses parallel LRC loop to improve power coupling efficiency between the lamp and the power switching circuit. The DC starter works at the low igniting frequency to offer open circuit protection for the starter itself.