Appendix; Backlighting; Inverter Power Supply - Panasonic TC-26LX20 Technical Manual

Appendix

Bac klighting
Backlighting Brightne ss fo r Panasonic's line of LCD TVs is accomplished through the
use of Cold Cathode Fluorescent tubes (CCFT), which is currently the light source of
choice, by a number of leading manufacturers.

Inverter Power Supply

Pulse width modulation is a very straightforward m ethod for controlling the brightness o f
the CCF tube(s). The inverter is turned on and off (using the input or an enable/disable
line) from the Microprocessor Unit (MPU) to contr ol the brightness. The "on" duty cycle
is lengthened to increase the brightness and reduced to decrease the brightness. One
of the major advantages of pulse width modulation is the tube is always fully "on" or fully
"off" and full starting voltage is always applied to the tube(s) (assuming nominal input
voltage). Figure 5 is a simplified diagram of a pul se width modulated DC to AC inverter.
Figure 32
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