par | Sep 21, 2010 | Non classé | 2 commentaires

We do not believe so well. At a time when the advent of the LED backlight is announced , people seem to want to bury CCFL backlights too quickly.

Why a second life ?

  • First of all because a CCFL powered by a piezoelectric inverter sees its lifespan almost double compared to the same power supplied by a conventional inverter with a transformer .
  • Then because apart from the presence of high voltage, a CCFL backlight with piezo inverter behaves like an LED backlight: efficiency of 90%, dimming from 0 to 100% !

A CCFL is a negative resistor. The more current you give it, the more its voltage drops. The more it heats up, the more its impedance drops: If it is not limited, it will always consume more current until it is destroyed.

A CCFL must therefore be driven by a constant current source . So why did we persist in coupling them to step-up transformers which are constant voltage sources incapable of regulating the variations in current passing through the CCFL according to its aging or the temperature?

A piezo inverter transforms a pulsed current into vibration in the piezoelectric transducer, then by reverse effect, this same vibration into high voltage at its end .

A feedback loop continuously monitors the current flowing through the fluorescent tube. Whether it’s hot or cold, whether the tube is new or has 5 years of good and loyal service behind it, it will always provide the same amount of light, where a backlight controlled by a traditional inverter will see its brightness drop almost linearly from the first day, until waiting 50% after 50,000 hours (in general). Why choose a very bright high-performance panel if its power supply is unable to allow it to remain so?!!

Because the current passing through the tube is sinusoidal and not a badly clipped square, the tube receives a sine at 50 KHz (in general) and that’s it. In transformer, it receives harmonics which do not generate any light but which heat it unnecessarily .

The temperature of a piezo-powered CCFL is 4 to 6°C lower than that of the same transformer-powered CCFL , at equal brightness of course. Also obvious EMC advantage: less harmonics and less level, less shielding cost!

The icing on the cake, the piezo inverters are electronically protected against short circuits and open circuits , giving perfect reliability to your equipment. The protections only cut the faulty output, allowing operation in degraded mode, where other inverter technologies will cut everything.

Many medium and large diagonal panels are still much too expensive in the LED version not to consider their CCFL version, especially if you want to operate from -40°c to +85°c as piezoelectric technology naturally allows. . Do not neglect also that if a CCFL has a low efficiency when cold, it does not fear heat, which is quite the opposite of the LED which likes the cold and ages more quickly when hot. The self-heating of the CCFL enough to restore its optimal performance in a short time, making any heating system unnecessary .

Thanks to its progressive voltage ramp on power-up (soft start), a piezo inverter starts all CCFLs with certainty, even the longest and greediest in start-up voltage (kick-off voltage). It will raise the voltage as long as necessary to create the ignition, but not more than necessary unlike the transformer which uses the CCFL unnecessarily, for lack of being able to vary its output voltage. As the piezo inverter is slaved, as soon as the ignition is detected, this elevation ceases and the CCFL is in stable and stabilized mode .

The MTBF is greater than one million hours per output , or for example 250 Khours for a 4-lamp model. Who says better ?

LCDIS will send you , on request, application notes explaining all these advantages in more detail – Contact us!