Datasheet

16
UCC1972/3
UCC2972/3
UCC3972/3
Since a fluorescent lamp is a pressurized gas filled tube
(usually Argon and Mercury vapor), it shouldn’t be sur
-
prising that temperature plays a major role in the lamp
characteristics. Fig. 13 depicts the variations in striking
and operating voltage for a 150 x 3mm lamp over tem
-
perature, illustrating the importance of taking tempera
-
ture effects into account when designing the converter.
The lumen output of the backlight system is temperature
dependent as well, and may need to be accounted for in
applications requiring tight lumens regulation over a wide
temperature range. Fig. 14 shows the temperature ef
-
fects on lumens for the lamp operated at 5mA.
Since lamp current is roughly proportional to luminosity, it
may be tempting to operate the lamp at a RMS current
higher than specified in the manufacturer’s data sheet.
While the lamp will continue to operate tens of percent
above the rated current, the luminosity gain becomes
less pronounced as the lamp is over-driven as shown in
Fig. 15. The expected life of the lamp will also degrade,
as illustrated in Fig. 16, when the lamp is operated above
rated current.
Cold Cathode Fluorescent Lamp Efficiency
Trade-Offs
Although CCFLs offer high output light efficiency com
-
pared to other lamp types such as incandescent, only a
percentage of the input energy is converted to light. As il
-
lustrated in Fig. 17, 35% of the energy is lost in the elec
-
trodes, 26% as conducted heat along the tube. A portion
of the Ultra Violet energy gets converted into visible light
by the lamp phosphor, where the remainder is converted
into radiated heat. Finally, Mercury atoms convert 3% of
the initial energy into visible light. The result is typically
15% overall electrical to optical energy conversion in the
lamp.
APPLICATION INFORMATION (cont.)
0
20
40
60
80
100
120
140
0 20406080
AMBIENT TEMPERATURE (°C)
LUMINANCE PERFORMANCE (%)
Figure 14. Temperature effects on lumens.
0
200
400
600
800
1000
1200
0 204060
AMBIENT TEMPERATURE (°C)
LAMP VOLTAGE (rms)
Striking Voltage 5mA
Figure 13. Temperature effects on voltage.
0
20
40
60
80
100
120
0246810
LAMP CURRENT (mA)
LUMINANCE PERFORMANCE (%)
5mA
RATED
LAMP
Figure 15. Lumens output versus current.
1
10
100
50 75 100 125 150 175 200
% RAT ED LAMP CURRENT
HOURS (1000's)
Figure 16. Lamp life versus current.