BS2 current draw in sleep while powered on Vin.

photomankc

I have a project where I am looking to create a low voltage shutdown for my batteries.· I am using the stamp to create a high/medium/low charge indicator and a timed load shutdown since the regulator is not a switcher.· I have a possible discrete circuit for total load shutdown if the batteries get too close to total discharge·but I was looking at the Stamp and noticed the module can take unregulated input too (I missed that at first).· I was wondering though if the low power sleep current draw applies if the stamps on-board regulator is running?· I was searching around but I wasn't having much luck finding that directly answered but several of the kits seemed to suggest that using the regulator negated the sleep savings which made sense.· It would save a lot of design and wiring if the stamp can draw that little on unregulated supply during sleep and I just use it to cut the regulated load off if the batteries drop below the trip point.

Mike Green

You'll have to look at the datasheet for the regulator. You didn't say what kind of Stamp you're using. The BS2 uses an LM2936 which is a low quiescent current regulator. The datasheet will have graphs showing the current drawn by the regulator in addition to the actual external current drain.

You'll have to go through the schematic looking at the various current drains in the Stamp module to come up with an exact current drain, but the quoted values for a BS2 are 3mA active and 50uA when sleeping or napping. This doesn't include any loads.

photomankc

The more I look the more I think it's only for the chip not the Vin with the on-board regulator. It doesn't appear to be anything but a linear reg so it's going to draw current no matter what the stamp is doing. It was a nice thought though. I'll probably need to stick with the separate voltage monitor circuit for this.

Tracy Allen

The 50 microamp figure does include the quiescent current of the regulator, Stamp powered from Vin. The Stamp in SLEEP or NAP or END modes drops down to less than 30 microamps for most of the time, but once every 2.3 seconds it wakes up briefly to check status and during that brief time it draws 2 milliamps. There is more info about the low power modes here:
www.emesys.com/BS2power.htm
However, nothing will go as low as a total cutoff switch, zero power.

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Tracy Allen
www.emesystems.com

photomankc

Sweet! That adds a twist then. The stand-alone cut off circuit drives a P-Type MOSFET high to cut the load and so it has to remain powered but it draws about 10 uA so it's of no real consequence. Even with just 100 mAh left in the batteries it would operate for weeks. The problem is that it involves several components and tweaking to get it to fire on the right voltage. The BS2, if I assumed 150uA to allow for more frequent polling of voltage, and an infrequent LED flash, would still operate for a week or two on the final bit of 6v juice remaining. That would be enough to allow for you to get the batteries out and charged.

The only issue it would raise is the short output flicker that happens when the stamp wakes. I could probably solve that with a R/C circuit to hold the P-Type MOSFET high and keep it from pulsing the load on and off too while the stamp drops the pin as it wakes.

Cool. I'll have to wrestle this around a bit in my head.