Understanding LCD Inverter Section And An Idea To Make Basic CCFL Tester
Flat-panel liquid LCDs are the display of choice in a wide range of
portable products from notebook Computers, tablet PCs, and PDAs to digital cameras and portable
instrumentation. Compact cold cathode fluorescent lamps (CCFLs) provide the necessary light illumination in
these applications, enabling a readable display in both dim and bright ambient light.
In LCD monitor and TV, CCFLs Inverter circuit plays an important
role in order to glow screen digitally. These are technically challenging circuits. First, inverters must
accept a wide range of dc input voltages, typically from 3 to 14 V, and provide ac outputs of 500 to 800 V to
run the CCFL tubes. Then, to burst into flames CCFL lamps, these circuits must provide momentary
Voltages that typically are twice that of their run voltages. Many
applications also require efficient
Dimming capabilities to allow lamp output to match ambient
(environment) light conditions and thus prolong both lamp and battery time.
There is more than one type of Inverter designs or topologies are
using in liquid crystal displays (LCD) devices. Such as:
1. Buck Royer Inverter (Traditional)
2. Direct Drive (Simplified
1. The traditional Buck/Royer inverter topology is essentially a combination of a
Buck Voltage regulator and a self-resonant Royer oscillator with an
integral step-up transformer. From one decade, display makers employed a Buck/Royer inverter topology to
strike and power CCFLs. This analog power topology is essentially a combination of a step-down Buck voltage
regulator and a self-resonant Royer oscillator with an integral step-up transformer.
Buck Royer Inverter
2.A simple inverter topology that could optimize performance, reduce component count,
and lower costs implements a Direct Drive
architecture that eliminates the inductor and resonant capacitors found in a conventional Royer
Direct Drive Inverter
Circuit Operation Of An
CCFLs, Inverter ideally takes DC-12 volts from power supply board
in LCD Monitor / TV and
In Laptop from NIMH Battery. The circuit operation and functions of
LCD inverter same like
Un-Interrupted Power supply (UPS)
In addition, LCD Inverter takes DC-12 Volts from supply and
starting signal pulse from main board, which fire the overall process in the inverter circuit. Switching is
present, so as to start the controlled oscillation through inverter dimming controller IC chip. Which
controls several functions.
For example, Short circuit protection, Temperature control, Power, Humidity and Dimming in order to error
free high and low CCFLs lighting. The most essential and compulsory section of an inverter is high
voltage transformer. Which produces up to 600- 800 Voltages output to match ambient light conditions and
requirements. It provides an alternating current source to drive the lamp. Lamp
current will be the total transformer Output voltage minus the lamp voltage (lamp voltage is inversely
proportional to current) divided by
the capacitor's impedance.
DC – 12 VOLT REGULATED POWER SUPPLY SCHEMATIC
The below regulated power adapter made for CCFLs tester circuit
supply and useful for other applications as per requirement. Its very simple circuit which uses center tape
step down transformer T1.
D1 and D2 provide full wave rectification and center tap use for
For filtration function uses C1, which kills the ripples of pulsating dc and to provide filter
In addition to this, there is one optional point, which use for
safety short circuit protection inside the circuit before regulator IC.
LM 7812 – chip is using to control surges and stability of DC 12
volts. Also, to be noted that R1 is using as fuse resistance.
CCFLs TESTER PCB DESCRIPTION: In below circuit, IC NE555 is
used to make
the multi-vibrator. The IC NE555 generates a square wave pulse
train. A preset VR1 -10K is used to adjust the frequency of this pulse train. In this circuit Pin No.3 of IC-
NE555 is use to output a 200 Hz square wave pulse train.
FLIP FLOP (COMPLIMENTARY IC):
IC2 –CD4013B is dual D-type flip – flop CMOS IC. Pin 11, which is input pin, is
provided with 200 Hz square wave signal from the IC – NE555. The CD-4013B divides this 200Hz signal into
two 50Hz bi-phase outputs. These outputs are available at
the pin no. 1 and 5 of CD-4013B IC2.
Inverter output transistor Q1 – D313 and Q2 – D313 are connected to
output transformer. Diode D3 and D4 function in dual mode. Iam using only one mode , In this mode they stop
the transistor voltages to error free operations.
When the output transformer works as LCD inverter, its last tapings
i.e. 600V, 680V and 750 Volts is used to get CCFLs testing supply by multi selector switch
facility. To be noted please put 400Volt / 2.2 capacitor between the high
voltage probe in order to synchronization.
To conclude all, there are several options available in technical
world to check the CCFLs tubes. Here is the basic circuit solution is providing in order to gain knowledge
purpose only. Any one can use above knowledge in order to make CCFLs tester at your own
Precautions must be taken to check CCFLs and tester
making or use.
In circuit Multi-Selector using for any type of CCFLs
tubes with respect to LCD sizes through selection procedures.
CCFLs, checking must be tested on low voltages
Above theory and designs are providing for knowledge
Author is not responsible for any type of Damages and Losses.
Make and use at you own risk.
All above information is providing on guidance and tips
Lab Engineer and
Hardware Workshop Incharge
SSUET, Karachi, Pakistan.
D.COM & DAE in Electronics.
B-Tech (Pass) in Electronics.
B-Tech (Hons) in Electronics.
A+ Certified, Brainbench Certified, Linux and
Computer & Electronics Specialist Certified.
The Author can be contacted at
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