PIEZO INVERTERS for BACKLIGHTS gives a second life to TFT modules

by | Jan 18, 2011 | Uncategorized | 0 comments

Second life is not a joke. Nowadays, everyone talks about LED backlights, some want to burry CCFL too fast.

Why such a second life ?

  • Until now, CCFL were powered by conventionnal inverters using transformers to make the DC to High Voltage AC conversion. A transformer is a constant voltage source which is bad, and the efficiency is average (65 to 70 %). They are not of very high reliability. They often had to be serviced before reaching the death of the CCFL lamps inside the panel they are driving.
  • A CCFL powered with a piezo inverter has a life nearly doubled compared to the case where it is driven by a transformer type inverter because piezo gives a real sinewave output, not a vaguely rounded square signal.
  • Apart from the presence of HV, using a piezo inverter offers the same features as a LED driver : 90%+ efficiency, 0-100% dimming
  • The MTBF of a piezo is 1 million hours
  • CCFL is a complex impedance mostly negative. The more current flowing into it, the lower the voltage. If not current limitation is done, it is going to self-destruction soon. The constant current source is the solution for this.

Other features exclusive to the piezo-electric technology :

It also solves the aging of the CCFL : impedance increases while aging. If the inverter is a voltage source, it means the current flowing into the lamp decreases day by day linearily (issue with transformers) according to the Ohm law.

Constant current piezo inverters compensate this as they are able to incrase their voltage so that the same current always flow : CONSTANT BRIGHTNESS during all the backlight life.No other technology does that.

servo loop continuously adjusts the current to keep it constant. Whether the temperature is low or high, whether the CCFL is new or aged, it will always delivery the nominal brightness.

During product selection stage, most enginers pay a lot of attention to select the brightness of the panel, paying little attention to this crucial part that is its backlight power supply. What if a cheap inverter doesn’t allow to maintain the performance all the time ? At 50Kh, an average backlight with traditionnal inverters only delivers 50% of the initial brightnessUse a piezo inverter and you’ll still get 100 %, and also during many extra tenth of thousands hours !

Piezo inverters are also much safer as they have a patented built-in open circuit and over-current protections that puts it instantly OFF until the problem is solved.It will only restart if the inverter power supply is removed and applied again.

This protection system is independant. On mulitple output inverters, only the failing output will be switched off, ensuring the panel operation until maintenance can be performed.

LED TFT panels availability

You have probably noticed that it is not yet possible to switch from CCFL to LED on all TFT panels sizes. First of all, some LED versions don’t exist yet for all sizes, but above all, the price is often higher.

Also if you plan to use outdoor a large panel designed for 0-50°c, what are the options ? Piezo is ! Piezo upgrade allows any well designed panel to operate on a much broader temeprature range safely and will even add reliability.

Forget prejudices about CCFL (” they don’t work at low temp”) : this is untrue and simplistic. A piezo inverter will strike ANY LAMP at -40°c without any expensive heating circuits. The efficiency at low temp is low, but in matter of a minute or two, the self-generated heat will bring your backlight back to its full brightness. No transformer type inverter can do this as it is unable to increase its strike voltage on demand when needed, but above all, automatically.

Piezo inverters also extend the life span as they have a soft start circuit that only gives the needed strike voltage needed, not more like conventionnal inverters. No premature aging due to repeated start up.

LCDIS is the exclusive distributor of ZIPPY TECHNOLOGY inverters since 2005.