Cooper CTX110655-R Ccfl transformer application note Datasheet

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 (Vstrike)
2. Running voltage (Vrun)
3. Frequency of operation (Fres)
4. Power (W)
5. Current (Ilamp)
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 pushpull 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 lowloss, 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.
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.
Use this formula to find the turn ratio needed to obtain the strike voltage of
the lamp.
Vstrike =
TR = Turns ratio
Vin min = Battery voltage
π × Vin min
2
× TR
The operating frequency of the system is determined by the inductance of
the primary and the bulk capacitor across the primary at resonance.
FRe s =
Coiltronics® Transformer Features:
1. Supply high voltage.
2. Operation frequency range from 40 to 80kHz.
1
2 × π LPr i × C Bulk
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.
Fres = Resonance Frequency
6. Operate in Royer and direct IC drive.
Determine the ballast capacitor value using the equation below.
Cballast =
7. 1500 volt primary to secondary isolation.
8. Ferrite core material.
I lamp
9. Designed for floating and non-floating applications.
2
2 × π × Fres (Vrun − Vsec )
10. Transformer secondary is machine wound on sections to increase
leakage inductance and reduce voltage gradient between layers.
Layout and Circuit Considerations
Vsec = Transformer secondary voltage
• The high voltage traces must be separated from low voltage traces.
Vrun = Lamp running voltage
• The ballast capacitor must be placed closer to the transformer secondary
pin.
Ilamp = Lamp current
• Avoid long wire connections from the transformer to the lamp. Stray
capacitance between wire and ground will reduce efficiency.
Fres = Resonance frequency
Cballast = Ballast capacitor
The capacitor voltage is 90 degrees out of phase with the lamp running
voltage.
• 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.
From this equation, determine the value of the ballast capacitor.
Schematic Relation to Part Number
Schematic A
Schematic B
Schematic C
Schematic D
Schematic E
CTX110652-R
CTX110655-R
CTX210403-R CTX110603-R
CTX110600-R
CTX410805-R
CTX210652-R
CTX110657-R
CTX210407-R CTX110605-R
CTX210600-R
CTX410807-R
CTX110659-R
CTX210409-R CTX110607-R
CTX210655-R
CTX210411-R CTX110609-R
CTX210657-R
CTX310403-R CTX110611-R
CTX210659-R
CTX310405-R CTX210603-R
CTX310407-R CTX210605-R
CTX310409-R CTX210607-R
CTX310411-R CTX210609-R
CTX210611-R
CTX410809-R
Part
Power
TR1
TR2
Number
Watts
Ns/Np
Np/FB
Lpri
μH
Vpri
Volts
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
CTX410805-R
CTX410807-R
CTX410809-R
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
4.00
4.00
4.00
4.00
4.00
4.00
4.00
4.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
6.00
14.00
14.00
14.00
67
67
86
100
67
67
86
100
50
86
100
125
50
86
100
125
67
50
67
86
100
125
67
50
67
86
100
125
67
86
100
6
6
2
4
6
6
2
4
6
4.7
4
4
6
4.7
4
4
6
6
6
4.7
6
4
6
6
6
4.7
6
4
5
4
4
43
43
26
19
43
43
26
19
44
27
20
20
44
27
20
20
44
44
44
27
20
20
44
44
44
27
20
20
24
16
16
20
20
15
13
20
20
15
13
26
15
13
10
26
15
13
10
20
26
20
15
13
13
20
26
20
15
13
13
30
23
23
Isec
DCRpri
mA max Ω max
5
5
5
5
5
5
5
5
7
7
7
7
7
7
7
7
12
12
12
12
12
12
12
12
12
12
12
12
30
30
30
0.220
0.220
0.212
0.190
0.220
0.220
0.212
0.190
0.220
0.160
0.160
0.160
0.220
0.160
0.160
0.160
0.160
0.160
0.160
0.132
0.132
0.132
0.160
0.160
0.160
0.132
0.132
0.132
0.030
0.024
0.024
DCRsec
Schematic
Mechanical
Ω max
Reference
Reference
285
285
285
285
285
285
285
285
165
220
220
330
165
220
220
330
176
132
176
176
176
291
176
132
176
176
176
291
262
272
314
A
B
B
B
A
B
B
B
C
C
C
C
C
C
C
C
D
C
C
C
C
C
D
C
C
C
C
C
F
F
F
A
A
A
A
C
C
C
C
B
B
B
B
D
D
D
D
E
E
E
E
E
E
F
F
F
F
F
F
G
G
G
Full primary turns used in turns ratio calculation.
Ns/Np= Turns Secondary/Turns Primary.
Np/FB= Turns Primary/FeedBack Winding.
Mechanical References
A
B
Mechanical References
C
D
E
F
G
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
• Unshielded Drum Inductors
• Toroidal 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.
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© 2008 Cooper Bussmann
St. Louis, MO 63178
636-394-2877
www.cooperbussmann.com
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