_24_V_from_two_to_three_cells

Published:2009/7/24 23:21:00 Author:Jessie | From:SeekIC

Figure 8-89 shows an LT1173 regulator connected to provide -24 V for LCD biasing using two AA cells. The 3-V input is converted to +24 V by the MOSFET switch in U1, inductor L, diode D1, and capacitor C1. The UI switch pin (SW1) then drives a charge pump composed of C2, C3, D2, and D3 to generate the -24 V.then regulation is less than 0.2% from 3.3-V to 2.0-V inputs. Load regulation, although it suffers somewhat because the -24-V output is not directly regulated, measures 2% from a 1-mA to 7-mA load. The circuit will deliver 7 mA from a 2.0-v input at 73% efficiency, and will also operate from a 5-V supply. LINEAR TECHNOLOGY, DESIGN NOTE 51, P. 1.



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