14

LT1513/LT1513-2

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.

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

20

µH

C2

4.7

µF

CERAMIC

C1

47

µF

ELECT

R4

20k

R3

10k

R5

330k

PWM DIMMING

(

≈1kHz)

5

1

2

3

10

6

T1

•

•

4

C5

4.7nF

C9

1

µF

C10

10nF

D1

3A

R1

470

Ω

C3

0.082

µF

WIMA

C4

27pF

3kV

LAMP CURRENT

5.6mA

NEGATIVE VOLTAGE

IS GENERATED HERE

R2

0.25

Ω

1513 F09

R7

2k

D2

15V

3

2

4, TAB

7

6

1

5

L2

20

µH

CCFL

C6

0.1

µF

+

•

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

GND

S/S

Figure 9. CCFL Power Supply for Floaing Lamp Configuration Operates on 2.7V