AN003 Datasheet, PDF (1/3 Pages) Analog Intergrations Corporation – Using AIC1650

AN003
High Efficiency LCD Bias Design by Using AIC1650
In general, black-and-white LCD display requires a
negative high voltage power source for gray-scale
contrast bias control. If this power is converted from
the 5V or 3.3V main power, often supplied from the
battery cells, a secondary conversion loss results.
This article introduce a design which provide a stable
negative voltage power source directly from the
battery with high power conversion efficiency.
LCD applications are becoming more and more
popular, especially for battery operated systems,
such like notebook computers, electronic
dictionaries, mobile phones, etc.. In some cases,
black-and-white LCDs require a negative high
voltage power source for gray-scale contrast bias
control.
Fig. 1 shows the basic topology of a Buck-Boost
DC/DC converter (switching regulator). The polarity
of output voltage is negative and magnitude can be
less than, equal to or greater than the input voltage.
The basic operation principle is using output voltage
feedback to control the ON-and-OFF state of the
power switch to obtain the specified output voltage
level. For low power applications, conventional PWM
control schemes are not ideal, because first, the low
conversion efficiency due to high switching losses as
compared to low output power, and second, the fact
that the PWM controller requires a minimum load to
maintain its stability. The most efficient and reliable
control method is then to use a
Pulse-Skipping-Modulation switching control, which
the control waveforms are shown in Fig. 2. This
switching control method can put the DC/DC
converter into quasi-sleeping mode under no load or
light load condition, which reduces switching losses
while maintaining high conversion efficiency and
good stability.
V_IN
V_IN
DRIVER
FB
DC/DC
CONVERTER
D
L
+
V_OUT
Fig. 1 The Basic Structure of the Inverting DC/DC Converter
May 1997
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