A full-digital dimming ballast with a digital power controller (DPC) for a fluorescent lamp

This paper presents a full digital ballast using a dedicated digital power controller (DPC) with a full digital control method. The proposed DPC is designed to have a variable frequency output pulse such as pulse frequency modulation (PFM) of 8 or 12-bits resolution, as well as a typical microcontroller feature including a sampled 8-bit A/D converter with an internal programmable memory. The variable frequency is used for driving the series-resonant network with a fluorescent lamp. By changing the driving frequency, the pre-heating feature is obtained. For protection purposes, the lamp current is monitored and can be used in a closed current loop. The DPC can also identify any fault conditions such as over-voltage, over-current, over-heat, strike fail, or a broken filament. Based on the programmable microcontroller feature, a highly intelligent ballast can be implemented. Experimental results for the 40 W, 48-inch lamp show that the proposed digital controller has a good dimming feature and it is possible to turn power devices on or off while the DC link power is live. It shows that power devices are well switched on with the zero voltage switching (ZVS) condition.