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Article: Battery automatic power-off has simpler design.(design ideas)
- Article from:
- EDN
- Article date:
- March 31, 2005
- Author:
CopyrightCOPYRIGHT 2005 Reed Business Information, Inc. (US). This material is published under license from the publisher through the Gale Group, Farmington Hills, Michigan. All inquiries regarding rights should be directed to the Gale Group. (Hide copyright information)
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A PREVIOUS DESIGN IDEA describes a simple way to automatically turn off a battery after a preset on period to save battery life (Reference 1). This Design Idea presents a simpler way to perform the same function (Figure 1). Two gates of [IC.sub.1], a quad two-input NAND Schmitt trigger, form a modified flip-flop. When you apply a 9V battery to the circuitry, the output of [IC.sub.1A] goes high because the initial voltage on [C.sub.1] is zero. The output of [IC.sub.1B] is LOW, which feeds back to [IC.sub.1A] through [R.sub.2], [C.sub.3] charges up through [R.sub.3]. The output of [IC.sub.1C] goes high because [R.sub.6] is connects to ground. A P-channel MOSFET switch, ...