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Maxim > Design Support > Technical Documents > Application Notes > Power-Supply Circuits > APP 1016
Keywords: inverting, dc-dc regulator, autotransformer, switching regulator, ICs, integrated circuit
APPLICATION NOTE 1016
Autotransformer Regulator Inverts 12V to -12V
Jul 09, 1998
Abstract: The autotransformer provides an alternative means of extending the output voltage range of an
inverting DC-DC regulator besides using an external MOSFET or a flyback transformer. With an
autotransformer, the input-output voltage can be extended beyond the specification limit of the integrated
circuit (IC).
In Figure 1, a dc-dc regulator with internal switching MOSFET inverts 12V to produce an output of
200mA at -12V. The IC is a high-efficiency device whose low quiescent current (120µA maximum) is
achieved with a CMOS process that limits the absolute maximum voltage to 21V (input to output). Thus,
to avoid 24V across its terminals, the IC must isolate itself from the inductor-flyback voltage by driving
either an external switch in a non-bootstrapped configuration, or an internal switch in a flyback-
transformer configuration.
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