Datasheet

14
LT1513/LT1513-2
sn1513 1513fas
TYPICAL APPLICATIONS
U
This Cold Cathode Fluorescent Lamp driver uses a Royer
class self-oscillating sine wave converter to driver a high
voltage lamp with an AC waveform. CCFL Royer converters
have significantly degraded efficiency if they must operate at
low input voltages, and this circuit was designed to handle
input voltages as low as 2.7V. Therefore, the LT1513 is
connected to generate a negative current through L2 that
allows the Royer to operate as if it were connected to a
constant higher voltage input.
The Royer output winding and the bulb are allowed to float in
this circuit. This can yield significantly higher efficiency in
situations where the stray bulb capacitance to surrounding
enclosure is high. To regulate bulb current in Figure 9, Royer
input current is sensed with R2 and filtered with R3 and C6.
This negative feedback signal is applied to the I
FB
pin of the
LT1513. For more information on this circuit contact the LTC
Applications Department and see Design Note 133. Consid-
erable written application literature on Royer CCFL circuits is
also available from other LTC Application and Design Notes.
2.7V
TO 20V
L1
20µH
C2
4.7µF
CERAMIC
C1
47µF
ELECT
R4
20k
R3
10k
R5
330k
PWM DIMMING
(≈1kHz)
5
12
3
10
6
T1
•
•
4
C5
4.7nF
C9
1µF
C10
10nF
D1
3A
R1
470Ω
C3
0.082µF
WIMA
C4
27pF
3kV
LAMP CURRENT
5.6mA
NEGATIVE VOLTAGE
IS GENERATED HERE
R2
0.25Ω
1513 F09
R7
2k
D2
15V
3
2
4, TAB
7
6
1
5
L2
20µH
CCFL
C6
0.1µF
+
•
Q2
Q1
C2: TOKIN MULTILAYER CERAMIC
C3: MUST BE A LOW LOSS CAPACITOR, WIMA MKP-20 OR EQUIVALENT
L1, L2: COILTRONICS CTX20-4 (MUST BE SEPARATE INDUCTORS)
Q1, Q2: ZETEX ZTX849 OR FZT849
T1: COILTRONICS CTX110605 (67:1)
LT1513-2
V
FB
V
IN
V
SW
I
FB
GND
S/S
V
C
Figure 9. CCFL Power Supply for Floaing Lamp Configuration Operates on 2.7V