MIC2172/3172

Micrel

4-28

1997

MIC3172

FB

COMP

C1

4.5V to 20V

EN

GND

P1 P2 S

Enable (On)

Shutdown (Off)

Cold Cathode

Fluorescent

Lamp

R5

Intensity

Control

R1

D1

R2

Q1

Q2

C2

C3

C4

C5

R3

R4

D3

1N4148

D2

1N4148

T1

L1

300µH

L1: Coiltronics CTX300-4P

T1: Coiltronics CTX110602

C2: Polyfilm, WIMA FKP2 0.1µF to 0.68µF

C4: 15pF to 30pF, 3kV min.

Figure 15. LCD Backlight Fluorescent Lamp Supply

On/Off Control

Especially important for battery powered applications, the

lamp can be remotely or automatically turned off using the

MIC3172’s EN pin. The entire circuit draws less than 1

µA

while shutdown.

Efficiency

To obtain maximum circuit efficiency careful selection of Q1

and Q2 for low collector to emitter saturation voltage is a

must. Inductor L1 should be chosen for minimal core and

copper losses at the switching frequency of the MIC3172, and

T1 should be carefully constructed from magnetic materials

optimized for the output power required at the Royer oscillator

frequency.

Suitable inductors may be obtained from

Coiltronics, Inc., tel: (407) 241-7876.