<Description>
<Invention Title> {INVERTER FOR EEFL AND BACKLIGHT}
<Technical Field>
This patent is about backlight inverter which supplies AC power for TFT-LCD panel.
The past TFT-LCD backlight inverter get divided into Buck-Royer circuit and exclusive
used-chip system in accordance with its method to use. Now generally use inverter for
CCFL(Cold Cathode Fluorescent Lamp). We choose and use a necessary system according to unit
cost or situations.
background Art>
Here we are going to explain backlight inverter for EEFL and similar structural Lamps.
EITL is made that electrode into exposing outer ii it replaces the •'/<?--■' r -nt of CCFL like
efficiency, life time and inverter cost. And EEFL is suitable large size panel.
Therefore, frequency in use and demand of EEFL is on an increasing trend to the panel
becoming larger.
But, when we use EEFL, there is a structural defect that can't receive feedback. So we could
not realize stable operating and protective function with the past inverter for CCFL.
This patent is about development of inverter which is stable and possible to protect by
complement this defect.
In addition, CCFL have two electrode, one is high voltage, the other is low voltage. Inverter
senses voltage passing the lamp again and uses this with feedback signal.
But, EEFL inverter can't receive feedback because both electrodes are connected to high
voltage side of transformer.
It is impossible to add the protective function and it is difficult to stable operating of
backlight inverter. That's why EEFL cannot be common in spite of its efficiency, life time
and cost better than other lamps.
we usually use backlight inverter's input supply DC power to rectify with 12V-24V, but this
power is on an high voltage trend. The circuit becomes complex the more the higher voltage.
There are more difficult to produce goods by common components.
This inverter solves these technical problems. It can applicate easily independent of DC
power's size. So it's possible to prepare of higher voltage here after.
The purpose of this patent is to make stable EEFL product and to lead EEFL m rket.
description of Drawings>
Figurel is block diagram of EEFL inverter,
Figure2 is the block diagram of existing CCFL inverter,
Figure3,4,5 are the explanations to sense feedback in EEFL inverter,
Figureβ is the explanation to sense each lamp's operations,
Figure7 is the circuit to operate high voltage FET using low voltage PM signal
<Disclosure>
<Technical Problem>
To make stable EEFL backlight inverter we must make the structure to sense stable feedback signal .
This is the point of this patent.
<Technical Solution>
This patent is about stable inverter using EEFL and similar structural lamps. Now explain with the figures.
In figurel, the inverter is consist of Input part(l), Control ρart(2), Operating part(3), Power part(4) and Output part(5). And external lamp(6) is connected.
Input part(l) is consist of input 'connector and this is the path ef DC. ower and external control signals.
•Control part(2) is consist of Buck-Royer circuit or exclusive used-chip. This part make PWM signals and transfer to Operating part(3). Also, this part accept feedback signal and control other functions.
Operating part(3) is consist of power FET. This part accept DC power, PWM signal and transfer power to transformer.
Power part (4) is consist of high voltage transformers. This part make high voltage AC power and supply the power to lamps.
Output part(5) is consist of output connectors. This is the path of high voltage AC power and
feedback signal .
In figure2, existing method, the EEFL(7) is connected to high voltage AC power from
transformerO) through the high voltage wire(lθ).
This method is not possible to receive stable feedback signal.
EEFL is possible parallel operating like in figure2.
The number of EEFL is changeable and figure2 is approximate.
This patent solve this problem with return wire etc. Below more explains.
<advantageous effects>
The needs of EEFL are on an increasing trend to the panel size becoming larger.
To use EEFL, we must develop the stable and capable- inverter .
If inverter have- defect or problems, we don't use EEFL.
This problems is caused by feedback signal and lack of design flexibility. EEFL is difficult
to sense stable feedback signal. This patent solve the problems and make more EEFL markets.
<Mode for Invent ion>
In figure3, we use the return wire(ll) to sense feedback signal. Secondary part of
transformerO) is connected EEFL directly. And return wire(ll) is connected high voltage
wire(lθ). Inverter board(8) is accept the signal through return wire and divide this signal
using devide resistor(12) and rectify using capacitor to get feedback signal level. This
feedback signal transfer to control par (2).
From this stable feedback signal, inverter can have protective functions and stable
operation.
Second method, in figure4, we devide and rectify secondary high voltage of transformer and
use feedback signal .
This method do not have return wires so do not detect lamp out situation, but it is possible
to operate stably.
Third method, in figureδ, we use return wire and use these signal like feedback. It is
similar to first method, this method is using antenna effect.
Return wire(ll) will be fixed to high voltage wire(lθ) using tape, glue or holding pin.
Turn ratio is changeable according to the EEFL's shape, size and voltage.
We use this signal to feedback, so we can make protective function in inverter.
From now on, We explain inverter that can sense each lamp's difference and malfunction.
This patent use light sensor, CDS, photo Transistor etc(15), to sense malfunction signals.
From this signals inverter knows each lamp's conditions and control.
In figureβ, the lamp holder(lβ) grasp the EEFL. Lamp holder is fixed to backlight panel (13).
Light sensor(15) is located to near EEFL to isolate from other lamp's lights.
The signal from light sensor is transfered to inverter board through the signal line(17).
Inverter calculate this signal with comparator or gate. And inverter can sense that lamp is
operating or not, and malfunction. So we can sense and prepare malfunction lamp and other
problems in long time operating.
Now we usually use DC voltage to 12V-24V range. This DC input voltage tend to high.
Here we explain inverter using the high voltage input power. Higher the input DC power, more
complicate and difficult to add another functions to the inverter circuits. Now we explain
the inverter that solved problems.
Figure7 shows the main driving circuit.
The- 5V level PWM(Pulse Width Modulation) -signal cannot operate high voiiage FET. This method
can operate high voltage FET by 5V level signal components. This method have design
flexibility like frequency adjusting, less component and timing control etc.
And easy apply to higher DC input voltage.
In figure7, high voltage DC power(~310V) is used the input power of inverter. To use common
IC, FET, and common parts it is necessary outer 10-20 volt level DC power or zener diode or
linear transformer.
Figure7 shows the circuit to operate high voltage FETs using 5V level PWM signals. High
voltage DC input power contributes the inverter's efficiency and functions.