Datasheet LT1513, LT1513-2 (Analog Devices) - 14

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