(57) Circuitry for providing unlimited, self-adjusted drive current and suitable for power
applications is described. A four terminal high efficiency, high gain driver circuit
(10) including enabling circuitry is provided along with a positive feedback loop
that is designed to provide unlimited drive current which automatically adjusts to
the load requirement. The driver circuit includes a startup transistor (14), drive
regulation transistors (12,13), predrive transistors (16,18), a driving output transistor
(17), and a current splitter (11). The drive regulation transistors (12,13) and the
current splitter (11) provide a positive feedback loop which supplies current to the
predrive transistors (16,18) and the driving transistor (17). Under typical conditions,
feedback loop operation will cause the collector to emitter voltage of the driving
transistor (17) to decrease which causes the drive regulation transistors (12,13)
to saturate. This condition decreases positive feedback loop drive which in turn regulates
the predrive current to the level required by the load. Under short circuit output
conditions, the drive regulation transistors (12,13), together with the current splitter
(11) and the sensing resistor (29), regulate the output drive current to a predetermined
level.
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