......... IF A technician plans to modify the Back Light CCFL lamp (a kind of fluorescent) an LCD to be A
Back Light Led lights.
Vcc voltage available Back Light on 12v POWER.
The total number of Back Light Led lights installed. is 27, so the required Back Light Inverter Out voltage is approximately 27 x 3v = 81v.
So i decided to buy the Universal Back Light Inverter type CA-255, because it met the requirements of "input voltage" and "output voltage".
But after installing and trying it ………
.. FET is so hot ... ..and it doesn't take long to die short.
What's wrong here ???
Where did it go wrong ???
Obviously .
This Universal Back Light Inverter is manufactured or designed "not for modification" from CCFL to LED
But this universal Back Light Inverter is actually made and designed to "replace" the defective Back Light Inverter circuit according to the existing Vcc input voltage and according to the number of existing led lamps.
Try to pay attention to the various voltage specifications of the Back Light Inverter led that we have ever encountered.
Each pay attention to the Vcc-Input voltage and Back Light-out voltage.
Then the Back Light-out voltage is generally a maximum of only 3 x the Vcc-input voltage.
So for example like the picture above.
To get 88v out voltage, the input voltage must be 28v.
Or more or less is 3 x the input voltage.
So from the example of the case story above.
The inverter has been forced with a Vcc input voltage of only 12v, .......... so that the output voltage is up to more than 80v.
This means that the output voltage is almost 7 x the Vcc input voltage.
This forces the PWM drive pulse width for the FET to be wider (longer on period) .... which causes the FET to heat up.
What is the solution to the example above ????
With an input voltage of only 12v ....... so to be safe the maximum output voltage should only be around 3 x 12v or 36v only.
So the solution is to change the total series of existing led lights ...
Changed to combined series - parallel.
For example, from 27 led …… ..diparallel into 3 parts…. Each part consists of 9 leds in series. So that the inverter output voltage needed is only around 9 x 3v or 27v.