VSUBOUT_SUB__BOOSTER

Published:2009/7/16 22:53:00 Author:Jessie | From:SeekIC

Step-up dc-to-dc converters that operate from small input voltages often possess correspondingly low maximum breakdown voltages of 5 to 6 V. This limits the maximum output voltage available from such devices. However, by adding an autotransformer, the output voltage (Vout) can be doubled without exceeding the IC's breakdown voltage. A properly wound center-tapped inductor acts like a transformer with a 1 : 1 turns ratio. Combined with an IC that typically boosts single-cell inputs as high as 6 V, it produces a regulated 9-V output with no more than 4.5 V across the IC (Fig. 1). The circuit can be applied in smoke alarms as well as in other battery-operated equipment. It delivers an output of 30 mA at 9 V from a 1.1-V input, and as much as 90 mA at 9 V from a 1.5-V input. A similar circuit setup for two-cell inputs delivers 30 mA at 9 V from 1.6 V, and a current of 80 mA at 9 V from 3.6 V (Fig. 2).



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