UCC3973 datasheet(16/26 Pages) TI2

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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.)

100

120

140

20406080

AMBIENT TEMPERATURE (°C)

Figure 14. Temperature effects on lumens.

200

400

600

800

1000

1200

204060

AMBIENT TEMPERATURE (°C)

Striking Voltage

5mA

Figure 13. Temperature effects on voltage.

100

120

024

LAMP CURRENT (mA)

5mA

RATED

LAMP

Figure 15. Lumens output versus current.

100

125

150

175

200

% RATED LAMP CURRENT

Figure 16. Lamp life versus current.

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