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Maxim > Design Support > Technical Documents > Application Notes > Power-Supply Circuits > APP 1864
Keywords: STN LCD, LCD contrast, triple-output regulated LCD supply, dual boost converter, step-up
converter. DC-DC converter
APPLICATION NOTE 1864
Regulated Dual Voltages Control STN-LCD
Contrast
Jan 31, 2003
Abstract: This design note shows how a single IC generates the dual voltages required to control
contrast in an STN LCD. The stable, dual-voltage LCD-contrast supply uses a dual-output boost
converter, the MAX1677, and only four Schottky diodes and two flying capacitors.
A similar version of this article appeared in the May 21, 2001 issue of Electronic Design magazine.
Generating a stable, dual-voltage, LCD-contrast supply can be difficult, especially if the two voltage
amplitudes must track each other with respect to a given reference level. In Figure 1, the ±20V outputs
are centered around a reference level (VM) of 3V. The contrast voltages must be symmetric about VM to
avoid a DC component across the liquid crystal, which in turn would damage the LCD or shorten its life.
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