Tech Briefs

Ultra-Low-Dropout Linear Regulator

A radiation-tolerant, ultra-low-dropout linear regulator can operate between –150 and 150 ºC. Prototype components were demonstrated to be performing well after a total ionizing dose of 1 Mrad (Si). Unlike existing components, the linear regulator developed during this activity is unconditionally stable over all operating regimes without the need for an external compensation capacitor. The absence of an external capacitor reduces overall system mass/volume, increases reliability, and lowers cost.

Linear regulators generate a precisely controlled voltage for electronic circuits regardless of fluctuations in the load current that the circuit draws from the regulator. To maximize the efficiency of the regulator, the dropout voltage (a measure of the voltage the regulator itself needs to operate) needs to be as small as possible. Existing regulators use p-channel transistors to minimize the dropout voltage, but p-channel regulators are intrinsically unstable and require an external compensation capacitor to stabilize their operation. The electrical properties of the compensation capacitor (in particular, its equivalent series resistance, ESR) must be well controlled to ensure stability. Changes in the ESR with temperature and/or radiation doses present challenges to stable regulator operation in extreme environments. This innovation allows an n-channel transistor to perform the regulation without the need for an external capacitor.

The n-channel pass transistor of the linear regulator operates in depletion mode thereby allowing ultralow dropout voltages of less than 100 mV.

This work was done by Trevor Thornton of Arizona State University and William Lepkowski and Seth Wilk of SJT Micropower for Goddard Space Flight Center. For further information, contact the Goddard Innovative Partnerships Office at (301) 286-5810. GSC-16097-1