MICROPOWER INVERTING
DC-DC CONVERTER
SC1652
January 29, 1998
TYPICAL APPLICATION INFORMATION
The typical application circuit generates an adjustable negative voltage for
contrast bias of LCD displays. Efficiency and output power can be opti-
mized by using the appropriate inductor and switch. The following formulas
provide a guideline for determining the optimal component values:
( ) L = 11.1−0.15× V+ ×
V+
IOUT × VOUT
PNP : VCEO > V + + VOUT
IC(MAX )
≥ 200 ×
IOUT
V+
VCE(SAT )
<
0.4
V
at
IC
=
200
×
IOUT
V+
and β
= 10
( ) RB ≅ 3 × L × V + − 0.8 , where units :V + in Volt, VOUT in Volt,
IOUT in Ampere,L in µH,
RB in Ohm.
© 1997 SEMTECH CORP.
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