Design Note 34 Issue 1 April 1996 High Efficiency Converter for LCD Bias Contrast Supplies DC Input +2.0V to +6.0V 22µF/10V C3 C2 0.1µF R2 V+ CS Maxim 749 DHI ADJ TR1 FMMT720 R1 DLOW 680R GND FB 47µH 1M RFB L1 RV1 1M D1 1N5819 C1 22µF/30V Vout = -17.0V COMP High Efficiency Negative Boost Converter. A high efficiency power supply based on the Maxim MAX749 for generation of the LCD bias contrast voltage is presented in this design note. The circuit requires an input of +2V to +6V and delivers an output of -17V at 50mA. Efficiency in the order of 80% is achieved using the FMMT720 - one of the very low VCE(sat) SOT23 PNP transistors available from the Zetex SuperSOT series. It is ideally suited for portable equipment and can be powered by two to five ‘AA’ size Ni-Cd batteries. DN34 - 1