Page 205 - The Art and Science of Analog Circuit Design

Tripping the Light Fantastic

Appendix C

A Lot of Cut-Off Ears and No Van Goghe—Some
Not-So-Great Ideas

The hunt for a practical CCFL power supply covered (and is still cover-
ing) a lot of territory. The wide range of conflicting requirements com-
bined with ill-defined lamp characteristics produces plenty of unpleasant
surprises. This section presents a selection of ideas that turned into disap-
pointing breadboards. Backlight circuits are one of the deadliest places
for theoretically interesting circuits the author has ever encountered.

Not-So-Great Backlight Circuits

Figure 11-C1 seeks to boost efficiency by eliminating the LT1172's satu-
ration loss. Comparator Cl controls a free running loop around the Royer
by on-off modulation of the transistor base drive. The circuit delivers
bursts of high voltage sine drive to the lamp to maintain the feedback

RELATIVELY LOW
FREQUENCY
Figure 11-C1,
A first attempt at
improving the basic
circuit. Irregular \ LAMP
Royer drive pro-
motes losses and
poor regulation.

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