An efficient dimming scheme for a plasma lighting system using solid-state power amplifier

An electrodeless plasma bulb is one of promising lighting source due to its high efficacy, long life time, and sun-like light spectrum. Recently, a plasma lighting system (PLS) using a radio frequency (RF) solid-state power amplifier (SSPA) as a power source of the plasma bulb is widely used instead of the conventionally used magnetron. The SSPA is easy to control an RF signal of the system, and therefore has benefit in dimming control. One of the simple dimming scheme is to control magnitude of continuous wave (CW) signal of the PLS. However, the efficiency of the SSPA degrades due to thermal problem for the CW signal. In addition, a power back-off for the dimming decreases the efficiencies of the SSPA and the PLS. To overcome this problem, a pulsed RF signal is used for the dimming of the PLS. A combination of switch-mode RF SSPA and pulsed RF signal can improve the efficacy of the PLS. In this paper, we propose an efficient dimming scheme by modifying the pulsed RF signal. In order to achieve better efficiency and linearity performances, the proposed RF pulsed signal has a slope in time-domain unlike the conventional pulsed RF signal that have rectangular shape. A spectral regrowth of the modified pulsed RF signal can be reduced by changing slope rate. In result, the adjacent channel leakage power ratio of the proposed method is less than that of the conventional pulsed RF signal. A PLS using the proposed dimming scheme shows better efficacy because it reduces return loss in the adjacent channel. A 2.47 GHz PLS with a 300 W gallium-nitride (GaN) SSPA is implemented, and it is used to verify the proposed method. The PLS using the proposed method shows better performance compared with those using the CW signal or the conventional pulsed RF signal.