_5_V_TO__7_V

Published:2009/6/30 2:24:00 Author:May | From:SeekIC

Uses LM555 timer as variable-duty-cycle pulse generator controlling transistor switchQ1 which in turn drivesflyback circuit.Regulator Q2-D3-R4-R5 varies duty cycle according to load, and flyback circuit L-D1-C1 develops negative output voltage. When Q1 is on, current flows through L to ground. When Q1 turns off, polarity across L reverses, diode becomes forward-biased, and negative voltage appears across C1 and load. When Q1 turns on again, voltage across L reverses for start of new cycle. Circuit eliminates separate transformer supply for negative supply of microprocessor. Efficiency is about 60%, load regulation 1.3%, and supply rejection 30 dB. Article gives design equations.—P. Brown, Jr., Converter Generates Negative μP Bias Voltage from +5V, EDN Magazine, Aug.5, 1977, p 42, 44, and 46.



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