Our company has made a variety of toys and consumer electronics that just use the connect-the-battery-directly method. They’re optimized for very low power usage when “off”, typically less than 10 uA draw, and around 1 uA for some. For alkaline batteries, this gives you standby times in years. They typically wake up in response to a button press that wakes the micro controller from deep sleep mode. You could probably get away with this for a lot of rechargeable battery designs as well, but I realize you don’t want your rechargeables 100% depleted. Self-discharge would do that eventually anyway, though.
Would using a battery charger/management IC be an option for you? You’re going to need some type of battery charger anyway, right? There are many of soft-power circuits that use virtually no power when off, but there are a lot of ICs on the market that will do exactly what you want (battery management, low battery detection, switching between dc input and battery, charge battery while running off DC, etc.). If you do want to use a soft-power circuit, what you described will work, with the drawback that the pulldown resistor will use power while the device is on. It can be a pretty large value resistor, though. If you OR the charger input with a control line from the uC through diodes, either one can keep the power on without back-driving the other. -Philip On Mar 18, 2015, at 9:05, David Madden <[email protected]> wrote: > I've done a bunch of "blinkenlights" -type projects, but my current > thing will need to be more polished and user-friendly. It's a small, > low-draw, battery-powered, output-mostly device. I think it shouldn't > have a power button; it really needs to be either "on," or "off because > it needs to be recharged." So I'm trying to figure out how to implement > this (other than just direct-wire the battery and let the device run the > battery completely flat.) > > I'm thinking about a low-side FET with a gate pull-down to control the > microcontroller ground connection. Connecting to the charger will pull > the gate up and turn on the uC, then the uC will keep its own power > turned on until it sees the battery get too low. Then, it'll turn > itself off by discharging the gate, and it'll stay off until connected > to the charger again. > > This seems a little dodgy to me, though, so I ask you professional > consumer-electronics people: what's a cheap, reliable way to turn the > power to a device on and off under the device's own control, without > requiring user interaction or a switch? > > Thanks, > -- > Mersenne Law LLP · www.mersenne.com · +1-503-679-1671 > - Small Business, Startup and Intellectual Property Law - > 9600 S.W. Oak Street · Suite 500 · Tigard, Oregon 97223 > > _______________________________________________ > dorkbotpdx-blabber mailing list > [email protected] > http://music.columbia.edu/mailman/listinfo/dorkbotpdx-blabber _______________________________________________ dorkbotpdx-blabber mailing list [email protected] http://music.columbia.edu/mailman/listinfo/dorkbotpdx-blabber
