LT1513/LT1513-2
U
TYPICAL APPLICATIONS
TheRoyeroutputwindingandthebulbareallowedtofloatin
this circuit. This can yield significantly higher efficiency in
situations where the stray bulb capacitance to surrounding
enclosureishigh.ToregulatebulbcurrentinFigure9,Royer
input current is sensed with R2 and filtered with R3 and C6.
This negative feedback signal is applied to the IFB pin of the
LT1513.FormoreinformationonthiscircuitcontacttheLTC
Applications Department and see Design Note 133. Consid-
erablewrittenapplicationliteratureonRoyerCCFLcircuitsis
alsoavailablefromotherLTCApplicationandDesignNotes.
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
havesignificantlydegradedefficiencyiftheymustoperateat
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.
C1
2.7V
47µF TO 20V
L1
ELECT
20µH
+
7
5
R3
10k
R2
0.25Ω
V
S/S
V
SW
IN
3
6
2
I
FB
C6
0.1µF
3
2
1
LT1513-2
•
V
FB
T1
C3
V
GND
C
0.082µF
WIMA
•
6
10
1
4, TAB
C2
4.7µF
CERAMIC
C4
D2
15V
R5
330k
27pF
3kV
•
5
CCFL
Q2
Q1
L2
20µH
R4
20k
4
LAMP CURRENT
5.6mA
C10
10nF
C9
1µF
NEGATIVE VOLTAGE
IS GENERATED HERE
R1
470Ω
C5
4.7nF
D1
3A
R7
2k
1513 F09
PWM DIMMING
(≈1kHz)
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)
Figure 9. CCFL Power Supply for Floaing Lamp Configuration Operates on 2.7V
14
Linear [ Linear ]
