| 摘要 |
<p>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.</p> |
