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CTX410809-R 参数 Datasheet PDF下载

CTX410809-R图片预览
型号: CTX410809-R
PDF下载: 下载PDF文件 查看货源
内容描述: CCFL变压器应用笔记 [CCFL Transformer Application Note]
分类和应用: 变压器电力变压器电源变压器
文件页数/大小: 4 页 / 563 K
品牌: COOPER [ COOPER BUSSMANN, INC. ]
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CCFL Transformer Application Note  
Cold Cathode Fluorescent Lamps (CCFLs) are used to illuminate Liquid  
Crystal Displays (LCDs). The LCD display is used in laptop computers, gas  
pumps, automobiles, test equipment, PDAs and medical instruments.  
CCFLs are small, efficient and inexpensive. The lamp must be driven by a  
specialized power supply. High sinusoidal AC voltage is needed to start the  
lamps, but once started, the voltage drops to a lower level. CCFL circuits  
are usually powered from a low voltage DC source of 5-12V. The DC to AC  
power supply needs a transformer to change low DC input voltage to high  
sinusoidal AC voltage.  
The Cooper Bussmann® Coiltronics® brand CCFL transformers are  
designed to work with inexpensive Royer class self-oscillating circuits. The  
Royer circuit works with input voltage from 2.5 to 20Vdc and is capable of  
producing 90% efficiency above 5Vdc input.  
Royer Diagram  
Transformer Selection  
The CCFL lamp manufacturer supplies the following lamp characteristics:  
1. Strike voltage (V  
)
strike  
2. Running voltage (V  
)
run  
3. Frequency of operation (F  
4. Power (W)  
)
res  
5. Current (I  
)
lamp  
The first step is to select the transformer according to the power  
requirement from the catalog.  
The second step is to decide the termination.  
A current-fed, push-pull topology is commonly used to power the CCFL  
transformer. This topology accommodates a wide input voltage and  
consists of a resonant push-pull stage, a Pulse-Width-Modulated (PWM)  
buck-derived control stage and a high-voltage secondary stage. The push-  
pull stage consists of transistors Q2 and Q3 to drive the center-tapped  
transformer T1. The transistors are driven 180° out of phase at 50% duty  
cycle with an auxiliary winding on the transformer. A resonant tank is  
formed between the primary inductance of the transformer and a low-  
loss, external resonant bulk capacitor C1. The resonant tank provides a  
sinusoidal voltage to the transformer’s primary winding and sets the  
system’s operating frequency.  
Use this formula to find the turn ratio needed to obtain the strike voltage of  
the lamp.  
π ×Vinmin  
Vstrike  
=
×TR  
2
TR = Turns ratio  
= Battery voltage  
V
The high voltage at the secondary of transformer is used to ignite and  
operate the lamp. Since the ignition or “strike voltage” is higher than the  
operating voltage, a high voltage ballast capacitor C2 is required to allow  
a voltage difference between the transformer secondary and the lamp. To  
minimize lamp stress and improve efficiency, the striking voltage  
waveforms should be sinusoidal.  
in min