Micrel, Incorporated

Steve I Chaney

Martin E Garnett

Andrew M Cowell

A start-up circuit for voltage regulators includes a depletion mode field effect transistor (FET) having a drain electrically coupled to an input voltage, a source electrically coupled to the voltage regulator power supply input terminal and to a voltage corresponding to an output voltage of the voltage regulator, a body at a fixed voltage, and a gate electrically coupled to the output of a comparator. At start-up, the voltage regulator is powered through the FET. The drain current is self-limiting, preventing the source of the FET from rising to the level of the input voltage. When the rising output voltage of the regulator reaches a level that can operate the regulator control circuit, the comparator grounds the gate of the FET to turn off the FET, and the voltage regulator operates off of its own output. Virtually no power is dissipated in the FET during steady-state operation of the regulator.

Start-up circuit for voltage regulators

A switching circuit has a pull-up FET and a pull-down FET coupled to a load circuit, each FET having a control terminal coupled to a current regulating circuit. The current regulating circuit provides a high predetermined current for a relatively short duration to the gates of the FETs to quickly turn on or turn off the FETs. After the short duration, a low quiescent current is applied to the gates to maintain the FETs in their present states. An inhibiting circuit, coupled between the pull-up FET and the pull-down FET, detects the states of the FETs and delays turn-on of one FET until the other FET has turned off. An overcurrent circuit monitors a current through a switching FET and turns off the FET after a predetermined time delay when an overcurrent condition is detected. The overcurrent circuit then turns on the FET after another predetermined time delay.

Growing community of inventors

Mountain View, CA, United States of America

Steve I Chaney