Ultracompact LCD Backlight Inverters A Svelte Beast Cuts High Voltage Down to Size

The liquid crystal display (LCD) has become ubiquitous. It is in use everywhere, from personal computers of all sizes to point-of-sale terminals as well as instruments, autos and medical apparatus. The LCD utilizes a cold cathode fluorescent lamp (CCFL) as a light source to back light the display. The CCFL requires a high voltage AC supply for operation. Typically, over 1000 volts RMS is required to initiate lamp operation, with sustaining voltages ranging from 200VAC to 800VAC. To date, the high voltage section of backlight “inverters” has been designed around magnetic transformers. A great deal of effort has been directed towards these ends, accompanied by a large volume of descriptive material.1 Unfortunately, as available circuit board space continues to shrink, magnetic transformer based approaches begin to encounter difficulty. In particular, it is highly desirable to fashion laptop computers with large area screens, leaving little room for the backlight inverter board. In many cases there is so little space available that building the inverter function inside the LCD panel has become attractive, although to date impractical.