Best way to run Propeller on batteries

william chan

Hi,

I need to run the propeller off 4 x AA Alkaline batteries.
I want to put the Propeller to sleep when it is idle to save on the batteries.
I also can't afford to waste the quiescent current of a 3.3v regulator when the propeller is asleep.
I hope to get the total board sleep current to less than 100uA.

What is the best way to do this?

Thanks.

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Philldapill

I'd use an ultra low power single opamp to regulate the voltage for the prop. You can get some with q current in the uA range easily. The simplest way might be to have an ultra low current reference like a 3.3V zener diode, and configure the opamp as a voltage follower, supplying power to the propeller directly.

Rayman

I think the best way is probably to use a switch mode supply chip...

I bought some LTC1308 single cell DC-DC converter chips recently, but haven't had the opportunity to try them out yet...

Beau Schwabe

william,

If you have an external event that would turn "ON" the Propeller, then see my reply to this thread...

Reference Thread: http://forums.parallax.com/showthread.php?p=730612

Schematic: http://forums.parallax.com/attachment.php?attachmentid=54043

..This circuit will keep you in low power standby mode somewhere in the nano amps.· Instead of the 5V regulator shown in the schematic, remove the 5V regulator and run the power output from the SCR (made of discrete transistors) directly to the 3.3V regulator instead.






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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 6/10/2008 3:27:48 PM GMT

Paul Baker

I agree with going with a switching regulator (which you could still use Beau's cicuit), but I would do something different. Instead of 4 AA batteries in series to produce 6V I would use a step up regulator and put the batteries in parallel. This effectively increases the mAh of your batteries and the regulator will continue output until the batteries are completely sucked dry.

If you use a modern 4 switch synchronous buck boost regulator you can achieve > 92% efficiency, while the older switching regulators get you 80 - 85% efficiency.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Post Edited (Paul Baker (Parallax)) : 6/10/2008 11:26:52 PM GMT

David E.

I'm assuming he needs the 4AA batteries for the rest of the device, in which case a switching regulator may work best. However if this device is using any kind of wireless I have had noise problems from switching regulators. Haven't done a project like that in a while but it was a problem for me.

(Of course he could still use a step up but I don't know what the current requirements are and I am not good at designing stuff from scratch)

william chan

Phill,
Which op-amp part number would you recommend? Which zener diode can reference 3.3v at at few microamps?
Why commercial 3-pin linear regulators cannot be based on such a voltage follower design to reduce the q current to uA range?

Rayman,
I searched LTC1308 at octopart.com and farnell but both sites does not know this IC.
What would be the q current for this part?

Beau,
Your SCR circuit is beautiful, but unfortunately sometimes I may need to go into low power mode instead of totally off.
The LM1117 3.3v regulator eats 4mA q current, so it is a problem for the batteries.
Which configuration use less current, 1Mhz crystal with 4x PLL or 4Mhz crystal with 1x PLL?

David,
You are right, I also need the 6v for running a stepper or servo motor.
Do you think the torque of the Parallax stepper motor would be too weak if run from 6v?


Thanks everyone, but the problem is still elusive.

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Post Edited (william chan) : 6/11/2008 1:10:15 AM GMT

David E.

Maxim has some low q current IC LDOs, q's in the micro amps. However, I don't know which to recommend as I have never used them and I don't know how much current you will need on the 3.3v side of things.

evanh

Forget using Alkaline's and go straight to NiMH. The new generation NiMH wipe the floor. They have higher capacity - something like 4x better, lower series resistance, priced similar, and best of all can hold a single charge for well over a year.

These newer NiMH's can be identified simply because they come precharged! Showing a level of confidence [noparse]:)[/noparse]

I think Sanyo were first off the blocks. en.wikipedia.org/wiki/Low_self-discharge_NiMH_battery


Evan

Phil Pilgrim (PhiPi)

Why not use CR123A lithium primary cells? They put out 3V and can drive the Propeller directly without any regulator. Also, they don't self-discharge (10-year shelf life); so you won't lose power capacity while the Propeller is loafing on standby.

-Phil

Ariba

Have a look at the LP2950/LP2951 regulators from National Semi.
The LP2950 is a 3 pin linear regulator with only 75uA quiesent current.
The LP2951 has also a Shutdown Input and an Undervoltage output.
Both are available at Digikey and cheap!

Andy

Jeff Martin

For powering steppers (I don't know how much torque you need) but I've found they have very little resistance to counter force unless you power them with 12 vdc.· I'm sure there are steppers out there that work at lower power with higher torque than the ones I've tested, but so far I haven't come across them.

I agree with Phil, the CR123A lithium primary cells are probably the best choice to directly power the Propeller with.· Like Paul was suggesting, you should probably·consider multiple cells in a parallel and/or series and parallel configuration where you could tap off 3 v for the Propeller and 9 v or 12 v for the steppers for the best performance as that will give you the different voltages you need and will afford you larger mAh.

I imagine that if your batteries are too drained to run the steppers, it doesn't matter if you still have enough power for the Propeller... but in case not, you could use something like the LT1307, it's q current is 50 uA, uses a boost mode for low demand situations and can take an input range of 1 to 5 vdc.· There's a number of other Linear Technologies regulators in the same class, but here's a page for this one:

http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1042,C1035,P1522


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--Jeff Martin

· Sr. Software Engineer
· Parallax, Inc.

Post Edited (Jeff Martin (Parallax)) : 6/11/2008 3:52:16 AM GMT

Philldapill

William,
I ran a quick search on TI.com and found a voltage regulator with 33uA quiescent current. They have some free SOIC-8 samples so you can order a few and try them out with your setup. I'm not sure if this really is the best way to go since you've had numerous people weigh in with other suggestions, but here's a link.

http://focus.ti.com/docs/prod/folders/print/tps76615.html

Praxis

Hi William,

Have a look at the MAX1705.

♦ Up to 96% Efficiency
♦ 1.1VIN Guaranteed Startup
♦ Up to 850mA Output (MAX1705)
♦ Step-Up Output (2.5V to 5.5V Adjustable)
♦ Linear Regulator (1.25V to 5.0V Adjustable)
♦ 1μA Shutdown Mode
♦ Voltage Monitor
♦ Pushbutton On/Off Control

I have included here a sample circuit.

Regards

Azlan

william chan

Wow !

These chips are amazing, especially the TI tps76615 with only 33uA q current!
But I think I will settle for the LP2950 b'cos they are available from Farnell and its simpler with 3 pins.

Thanks everyone.



Azlan,
I am still afraid to go with switching regulators.....
How's your Propeller project coming along?

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Praxis

Hi William,

Project going well, design finished now waiting for prototype PCB's to come back.

I am going to need a few P8X32A-Q44's for the prototypes, I will give you a call later.

In the meantime why don't you like switching regulators?

Regards

Azlan

evanh

Using non-rechargeables for a power application is wasteful. And no need for any button cells either. The primary Vcc capacitor should be enough storage to sustain the sleeping Prop during a battery change and an active Prop during brown-outs.

Some calculations are in order me thinks, on how much energy will be needed for each move and also how often are moves performed and finally how long do you want between battery changes.


Evan

Fred Hawkins

Surfed to this chip today: http://www.ti.com/corp/docs/landing/tps63000/

datasheet: http://focus.ti.com/lit/ds/symlink/tps63000.pdf

report on·it's intended use of extending·Li-ion life: http://focus.ti.com/lit/an/slyt256/slyt256.pdf

TI's intro page said...

[font=Verdana, Arial, Helvetica, sans-serif]The new TPS63000 buck-boost DC/DC converter delivers up to 96% peak efficiency over a wide input voltage range of 1.8 V to 5.5 V up to 1.2 A. Extending battery life in one-cell, Li-Ion-powered multimedia handhelds, the TPS63000 provides up to 28% greater run-time compared to a standard buck converter with a 3.3-V output – all from a space-saving 3 x 3 mm² QFN package.[/font]


and from the product page...

The TPS6300x devices provide a power supply solution for products powered by either a two-cell or three-cell alkaline, NiCd or NiMH battery, or a one-cell Li-Ion or Li-polymer battery. Output currents can go as high as 1200 mA while using a single-cell Li-Ion or Li-Polymer Battery, and discharge it down to 2.5V or lower. The buck-boost converter is based on a fixed frequency, pulse-width-modulation (PWM) controller using synchronous rectification to obtain maximum efficiency. At low load currents, the converter enters Power Save mode to maintain high efficiency over a wide load current range. The Power Save mode can be disabled, forcing the converter to operate at a fixed switching frequency. The maximum average current in the switches is limited to a typical value of 1800 mA. The output voltage is programmable using an external resistor divider, or is fixed internally on the chip. The converter can be disabled to minimize battery drain. During shutdown, the load is disconnected from the battery. The device is packaged in a 10-pin QFN PowerPAD™ package measuring 3 mm × 3 mm (DRC).

Looks like this could be the chip to use for me; the 63001 is 3.3v version.

Post Edited (Fred Hawkins) : 6/14/2008 3:07:32 PM GMT

DarrenY

Check out the Linear LT1529 3A Low Dropout Regulators with Micropower Quiescent Current and Shutdown.

From the data sheet:

"The LT®1529/LT1529-3.3/LT1529-5 are 3A low dropout
regulators with micropower quiescent current and shutdown.
The devices are capable of supplying 3A of output
current with a dropout voltage of 0.6V. Designed for use
in battery-powered systems, the low quiescent current,
50μA operating and 16μA in shutdown, make them an
ideal choice."

Ale

What about a Gold Cap, are they overkill ? Do they charge slowly or fast, I think I read somewhere that they do not charge that fast....