MIC2172/3172
On/Off Control
Micrel
Efficiency
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 1µA
while shutdown.
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
copperlossesattheswitchingfrequencyoftheMIC3172,and
T1 should be carefully constructed from magnetic materials
optimizedfortheoutputpowerrequiredattheRoyeroscillator
frequency. Suitable inductors may be obtained from
Coiltronics, Inc., tel: (407) 241-7876.
Cold Cathode
T1
Fluorescent
Lamp
BF
C4
R2
VIN
4.5V to 20V
Q1
Q2
D2
D3
eSc
rPi1
D1
1N4148
1N4148
C2
C3
VIN
L1
Enable (On)
EN
VSW
FB
Shutdown (Off)
rPi2
MIC3172
300µH
R3
C5
R4
GND
R5
Intensity
Control
P1 P2 S COMP
R1
C1
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
4-28
1997
MICREL [ MICREL SEMICONDUCTOR ]
