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Contents
ANP005
Application Note

AP2001 CCFL Inverter



This application note contains new product information. Diodes, Inc. reserves the right to modify the product specification without notice. No liability is
assumed as a result of the use of this product. No rights under any patent accompany the sale of the product.
1/15
ANP005 App. Note 1
Dec 2002

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© Diodes Incorporated

Contents


1. AP2001
Specifications
1.1 Features
1.2 General
Description
1.3 Pin
Assignments
1.4 Pin
Descriptions
1.5 Block
Diagram
1.6 Absolute Maximum Ratings

2. Hardware
2.1 Introduction
2.2 Description of the CCFL Inverter Circuit
2.3 Input / Output Connections
2.4 Schematic
2.5 Board of Materials
2.6 Board
Layout

3. Design
Procedures
3.1 Introduction
3.2 Operating
Specifications
3.3
Design
Procedures
3.3.1 Current Regulating Buck Converter
3.3.2 Royer-Type Resonant Oscillator
3.3.2.1
Selection of the Transformer (T)
3.3.2.2
Selection of the Ballast Capacitor (CY)
3.3.2.3
Selection of the Resonant Capacitor (CR)
3.3.2.4
Selection of the Push-Pull Transistors (Q)
3.3.2.5
Brightness Adjust of the Lamp














ANP005
Application Note

AP2001 CCFL Inverter



2/15
ANP005 App. Note 1
Dec 2002

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1. AP2001 Specifications
1.1 Features
- Dual PWM Control Circuitry
- Operating Voltage can be up to 50V
- Adjustable Dead Time Control (DTC)
- Under Voltage Lockout (UVLO) Protection
- Short Circuit Protection (SCP)
- Variable Oscillator Frequency...... 500KHz Max
- 2.5V Voltage Reference Output
- 16-pin PDIP and SOP Packages

1.2 General Description
The AP2001 integrates Pulse-width-Modulation (PWM) control circuit into a single chip, mainly designs
for power-supply regulator. All the functions include an on-chip 2.5V Reference Output, two Error Amplifiers,
an Adjustable Oscillator, two Dead-Time Comparators, UVLO, SCP, DTC circuitry, and Dual Common-Emitter
(CE) output transistor circuits. Recommend the output CE transistors as pre-driver for driving externally. The
DTC can provide from 0% to 100%. Switching frequency can be adjustable by trimming RT and CT. During
low VCC situation, the UVLO makes sure that the outputs are off until the internal circuit is operating normally.
1.3 Pin Assignments

1
2
3
15
14
13
12
11
10
9
8
7
6
5
4
16
CT
EA2+
EA2-
FB2
DTC2
OUT2
VCC
GND
OUT1
DTC1
FB1
EA1+
RT
REF
SCP
EA1-
( Top View )
PDIP/SOP

1.4 Pin Descriptions
Name
Description
CT Timing
Capacitor
RT Timing
Resistor
EA+ Error
Amplifier
Input(+)
EA -
Error Amplifier Input(-)
FB
Feedback Loop Compensation
DTC Dead
Time
Control
OUT Pre-driver
Output
GND Ground
VCC Supply
Voltage
SCP
Short Circuit Protection
REF Voltage
Reference

© Diodes Incorporated

ANP005
Application Note

AP2001 CCFL Inverter



3/15
ANP005 App. Note 1
Dec 2002

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1.5 Block Diagram
Bandgap
Reference
DTC2
REF
OUT1
OUT2
PWM Amplifier 2
PWM Amplifier 1
EA1 +
EA1 -
VCC
Oscillator
RT
SCP
CT
DTC1
Error Amplifier 1
FB1
EA2+
EA2 -
Error Amplifier 2
FB2
R
S
VREF
UVLO
R
MAX.500KHz
GND
170K
1.18V
+-
+
-
+
+
+
+
-


1.6 Absolute Maximum Ratings

Symbol
Parameter
Rating
Unit
V
CC
Supply Voltage
40
V
V
I
Amplifier Input Voltage
20
V
V
O
Collector Output Voltage
40
V
Io
Collector Output Current
21
mA
T
OP
Operating Temperature Range
-20 to +85
o
C
T
ST
Storage Temperature Range
-65 to +150
o
C
T
LEAD
Lead Temperature 1.6 mm (1/16 inch) from Case for 10 Seconds
260
o
C









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Application Note

AP2001 CCFL Inverter



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2. Hardware

2.1 Introduction

The CCFL presents a highly nonlinear load to the converter. Initially when the lamp is cold (inoperative
for some finite time), the voltage to fire the lamp is typically more than three times higher than the sustaining
voltage. The lamp characteristic fires at 1800V and exhibits an average sustaining voltage (Vn) of 600V.
Notice that the lamp initially exhibits a positive resistance and then transitions to a negative resistance above
1mA. These characteristics dictate a high output impedance (current source) drive to suppress the negative
load resistance effect and limit current during initial lamp firing. Since the ZVS (zero voltage switched)
converter has low output impedance, an additional lossless series impedance such as a coupling capacitor
must be added. To facilitate analysis, the equivalent CCFL circuit (shown in figure 1) is used. VFL is the
average lamp sustaining voltage over the operating range. The lamp impedance (RFL) is a complex function,
but can be considered a fixed negative resistance at the sustaining voltage. Stray lamp and interconnect
capacitance are lumped together as CCFL.
Figure 1. CCFL equivalent circuit

The CCFL inverter demo board supply 2~4 pcs lamp. This board can supply output power up to 8.4W for
every transformer output (600Vrms / 14mA). Using a dc input voltage of 10.8 V to 13.2 V, The control method
used in the board is fixed frequency, variable on-time pulse-width-modulation (PWM). The feedback method
used is voltage-mode control. Other features of the board include under voltage lockout (UVLO), short-circuit
protection (SCP), and adjustable dead time control (DTC).
C
FL
R
FL
V
FL









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Application Note

AP2001 CCFL Inverter



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2.2 Description of the CCFL inverter circuit

The CCFL inverter circuit is comprised of the current regulating buck converter and the Royer-type
resonant oscillator. The buck converter controls the magnitude of CCFL current. This feature is instrumental in
providing dimming control. The Royer-type resonant oscillator circuit is shown in Figure 2.


Vcc
PWM control
L
B
D
C
R
L
m
L
m
T
C
Y
C
Y
0
0.7
0
0.7
Figure 2. Royer-type Resonant Oscillator Circuit


Figure 3. Simplified Royer-type Resonant Oscillator Circuit

4C
R
L
m
C
Y
R
L
/ 2
I
L
2

Royer-type Resonant Oscillator

The circuit shown in Figure 2 is essentially a current fed parallel loaded parallel resonant circuit, which
can be further simplified to that shown in Figure 3. The simplification in Figure 3 assumes that two lamps are
operating in parallel. If one lamp is used then the original output ballast capacitor value should be used in the
calculations. L
m
is the magnetizing inductance of the inverter transformer, which tunes with the resonant
capacitor C
R
to set the resonant frequency of the inverter. The oscillator frequency of the AP2001 is set lower
than the resonant frequency to ensure synchronization. The current source labeled IC in Figure 2 is a
conceptual current-fed which models the function of L
B
.





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ANP005
Application Note

AP2001 CCFL Inverter



6/15
ANP005 App. Note 1
Dec 2002

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Buck Converter

The Buck converter converts a DC voltage to a lower DC voltage. Figure 4 shows the basic buck topology.
When the switch SW is turned on, energy is stored in the inductor L and it has constant voltage V
L
= V
i

V
o
,
the inductor current iL ramps up at a slope determined by the input voltage. Diode D is of