MICROPOWER_STET_UP_CONVERTER

Published:2009/7/13 1:48:00 Author:May | From:SeekIC

This circuit can start with inputs as low as a diode drop, i.e., 0.6 V. It provides a 5-V output with 15-mA current capability, but for this application, the load current must be limited. The circuit pow-ers a meter from the drop across a single diode in a 4- to 20-mA current loop, and provides 77 percent efficiency at a current of 0.5 mA (with diode D6 shorted). Load current available to the meter (Iload) is limited by the 4-mA minimum loop current. Transistor Q1 and transformer T1 form a resonant tank circuit that self-oscillates at a frequency of approximately 1/L1R1.R1 is a current-limiting resistor. At 50 kHz, with an input of 0.6 V, the value shown for resistor R1 (33 Ω) limits the maximum current into the base of transistor Q1 to 20 mA. The primary inductance of transformer T1, although not a crucial parameter, should be 660 μH for this value resistor of R1.



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