asserts its output P1.1 low to turn off Q2 and, consequently, Q1, removing power from the system until the user presses S1 and restarts the process.

　　When selecting components, ensure that Q1's gate-source breakdown voltage exceeds the highest possible input voltage; otherwise, use a zener diode to limit Q1's applied gate-source voltage. You CAN omit Q1 if voltage regulator IC1 includes an on/off-control PIN. To replace Q1 with a different power-switching device, such as an NPN bipolar transi

stor or a relay, specify Q2 to provide the control current that the switching device requires. To further reduce the circuit's component count, replace diodes D1 and D2 with a suitable common-cathode dual-diode array, such as the BAV70. Omit resistor R3 if IC2 includes built-in pullup resistors, as do many modern microcontrollers.

　　Reference

　　Hageman, Steve, "Single switch serves dual duty in small, microcontroller-based system," EDN, March 30, 2006, pg 96. 

　　英文原文地址： http://www.edn.com/article/CA6372827.html

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