CTX110603-R [COOPER]

CCFL Transformer Application Note; CCFL变压器应用笔记


型号：	CTX110603-R
厂家：	COOPER BUSSMANN, INC.
描述：	CCFL Transformer Application Note CCFL变压器应用笔记变压器
文件：	总4页 (文件大小：563K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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 ×V_inmin

V_strike

×TR

TR = Turns ratio

= Battery voltage

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

Coiltronics^®Transformer Features:

1. Supply high voltage.

The operating frequency of the system is determined by the inductance of

the primary and the bulk capacitor across the primary at resonance.

2. Operation frequency range from 40 to 80kHz.

3. Deliver output power from 2.5 to 14 watts.

4. Slim or low profile type easily built into your design.

5. Available in through-hole and SMT recess or gull wing type.

6. Operate in Royer and direct IC drive.

F_Res

2 ×π L_Pri×C_Bulk

Fres = Resonance Frequency

Determine the ballast capacitor value using the equation below.

7. 1500 volt primary to secondary isolation.

8. Ferrite core material.

I_lamp

9. Designed for floating and non-floating applications.

C_ballast

2 ×π × F_res(V_run−V_sec)

10. Transformer secondary is machine wound on sections to increase

leakage inductance and reduce voltage gradient between layers.

Layout and Circuit Considerations

•The high voltage traces must be separated from low voltage traces.

= Transformer secondary voltage

= Lamp running voltage

= Lamp current

sec

•The ballast capacitor must be placed closer to the transformer secondary

pin.

run

lamp

•Avoid long wire connections from the transformer to the lamp. Stray

capacitance between wire and ground will reduce efficiency.

= Resonance frequency

= Ballast capacitor

res

•Incorporate open lamp and overload protection in the circuit design. Open

lamp will cause full voltage in the transformer output and will burn the

transformer. Most of the CCFL IC has protection built in the circuit for

open and overload condition.

ballast

The capacitor voltage is 90 degrees out of phase with the lamp running

voltage.

From this equation, determine the value of the ballast capacitor.

Schematic Relation to Part Number

Schematic A

CTX110652-R

CTX210652-R

Schematic B

CTX110655-R

CTX110657-R

CTX110659-R

CTX210655-R

CTX210657-R

CTX210659-R

Schematic C

Schematic D

CTX110600-R

CTX210600-R

Schematic E

CTX410805-R

CTX410807-R

CTX410809-R

CTX210403-R CTX110603-R

CTX210407-R CTX110605-R

CTX210409-R CTX110607-R

CTX210411-R CTX110609-R

CTX310403-R CTX110611-R

CTX310405-R CTX210603-R

CTX310407-R CTX210605-R

CTX310409-R CTX210607-R

CTX310411-R CTX210609-R

CTX210611-R

Part

Power

TR1

TR2

DCR

Schematic Mechanical

pri

sec

pri

sec

Number

Watts Ns/Np Np/FB

μH

Volts mA max Ω max

Ω max Reference Reference

CTX110652-R

CTX110655-R

CTX110657-R

CTX110659-R

CTX210652-R

CTX210655-R

CTX210657-R

CTX210659-R

CTX210403-R

CTX210407-R

CTX210409-R

CTX210411-R

CTX310403-R

CTX310407-R

CTX310409-R

CTX310411-R

CTX110600-R

CTX110603-R

CTX110605-R

CTX110607-R

CTX110609-R

CTX110611-R

CTX210600-R

CTX210603-R

CTX210605-R

CTX210607-R

CTX210609-R

CTX210611-R

2.5

100

4.7

0.220

0.212

0.190

0.220

0.212

0.190

0.220

0.160

0.220

0.160

0.132

0.160

0.132

0.030

0.024

285

165

220

330

165

220

330

176

132

176

291

176

132

176

291

262

272

314

4.00

6.00

100

125

100

125

100

125

100

125

100

CTX410805-R 14.00

CTX410807-R 14.00

CTX410809-R 14.00

Full primary turns used in turns ratio calculation.

Ns/Np= Turns Secondary/Turns Primary.

Np/FB= Turns Primary/FeedBack Winding.

Mechanical References

The Cooper Bussmann^®Coiltronics^®brand of magnetics specializes in standard and custom solutions, offering the latest in state-of-the-art low-profile

high power density magnetic components. We remain at the forefront of innovation and new technology to deliver the optimal mix of packaging, high

efficiency and unbeatable reliability. Our designs utilize high frequency, low core loss materials, and new and custom core shapes in combination with

innovative construction and packaging to provide designers with the highest performance parts available on the market. The Coiltronics Brand product line

of power magnetics continually expands to satisfy shifts in technology and related market needs. Standard Product Categories include:

• Shielded Drum Inductors

• Toroidal Inductors

• Unshielded Drum Inductors

• Specialty Magnetics

• High Current Inductors

• Custom Magnetics

Please visit http://www.cooperbussmann.com/datasheets/elx to see the wide variety of inductor solutions we have to offer.

Order samples online - www.cooperbussmann.com

St. Louis, MO 63178

636-394-2877

www.cooperbussmann.com

Reorder # 4035

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