ultra Low DropOut regulator and Buck/Boost for solar applications

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Offline bwh13

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ultra Low DropOut regulator and Buck/Boost for solar applications
« on: 01 / September / 2013, 02:26:19 »
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Hi All,
I needed a voltage regulator for a solar battery operated time lapse camera.  I would get a full 6V from the panel if the sun was good.  This ended up shutting down the camera mid-script.

ultra LDO

I worked an Adafruit forum and they turned me on to the ultra LDO voltage regulator.  I ended up getting the Texas Instruments LP3964 linear regulator.  It has a dropout voltage of 24mV at 80mA.  The regulator has 5 leads (bent and staggered! very cool looking: not breadboard friendly without manipulation.)  I followed the circuit diagram and the 'Application Hints' on the datasheet.  Specifically relating to calculating how big a trim. pot. to use as R2, the sizing of the caps, and tying the Shutdown pin in to the Voltage In pin. 

I've included a couple of pics of the rig and the circuit diagram below.  I'd be glad to put together a component list if anyone is interested.

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Offline bwh13

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Re: ultra Low DropOut regulator and Buck/Boost for solar applications
« Reply #1 on: 01 / September / 2013, 02:41:34 »
Hi All,

Buck / Boost

While I was researching the components for the uLDO, I came across this Buck/Boost unit on Pololu.

I set the output voltage to 3.9V and installed it in my solar battery time lapse rig (running the Ultimate Intervalometer script)over a week ago and it's been shooting on the 30 minute mark since then.  It takes shots between 0600 - 2200 and reboots every night.  So I am ~210 shots into this field test as of today.  It's a small panel and I have been able to reposition it during the day for most days.

My impressions thus far: It must be regulating the 6V from the panel pretty well to be running this long -> which was the problem to begin with.  I don't have an idea about how low the battery is being drained each day, though.  I'm logging everything to a script so I can do a post-mortem on the exercise, but until then, I'm kinda stacking the deck in favor of the battery by optimizing the position of the panel throughout the day.  I will post that data when I've concluded the test.

Re: ultra Low DropOut regulator and Buck/Boost for solar applications
« Reply #2 on: 01 / September / 2013, 06:34:11 »

While I was researching the components for the uLDO, I came across this Buck/Boost unit on Pololu.

As I mentioned in earlier posts regarding long-duration time-lapse, I use that regulator with a lead-acid battery on all my time-lapse rigs.
I have ten of them and despite the warnings they do not get hot enough to burn you (in my application) !

The potentiometer is extremely sensitive in the higher voltage part of the range and almost impossible to set a precise voltage.

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Offline bwh13

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Re: ultra Low DropOut regulator and Buck/Boost for solar applications
« Reply #3 on: 01 / September / 2013, 12:53:57 »
With regards to the Buck/Boost: I'm assuming that it uses up a bit of juice to boost up to the desired voltage. Do you have any idea how much?  It seems like there might be a diminishing return at some point: the lower that your battery drops below the output, the more it uses to boost the voltage. It might not be an issue with your big lead-acid rigs, but I'm working with a 6A LiPo in a remote location (20 miles off the road in the wilderness.)

I guess what I'm trying to assess and pick up from other users, is does either rig (buck/boost or LDO) offer a clear advantage over the other in terms of battery life?

My thoughts are that a simple LDO would be less work for a battery rig because it won't use up extra voltage / amps to 'boost' the voltage to the desired range.  The other side of that coin is that the buck/boost could use more of the battery where the simple LDO would shut off.  Is my logic in the realm of reality or am I missing something?

Thanks for your attention!


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Offline ahull

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Re: ultra Low DropOut regulator and Buck/Boost for solar applications
« Reply #4 on: 01 / September / 2013, 17:41:23 »
Sadly there is no quick and simple answer to the question. However hopefully this might help.

Buck converters or buck regulators tend to be more efficient than Low-dropout liner ones, however that is a bit of a generalisation.

For some applications there is little to choose between them. For example a typical LM2596 design will theoretically be 95% efficient, but only when the input and output voltages are relatively high (see efficiency, fig 5 page 6). If however we run it with low input and output voltages, its efficiency may be much lower (<70% for 5V input and 3.7V output). This does not mean they are a bad choice for this application, as simple linear regulators are often much worse in terms of simple efficiency.

Both types of regulator have their advantages and disadvantages.     

One of the typical applications of these cheap LM2596 regulator modules is as a solar regulator, where the somewhat variable output of a solar panel array (with a nominal output voltage of perhaps 24V ) is used to charge a 12V sealed lead acid battery. In this application, you could expect 90% plus efficiency, with little energy wasted as heat.

Running a 3.7V camera directly from the LM2596 might not be so effective as the output voltage is relatively low, so we might waste a bit more power. The most efficient solution would be to run the camera directly from a large 3.7V LiPo... however high capacity 3.7V LiPo/LiIon batteries are few and far between (and thus expensive). Therefore we will need to compromise between efficiency and utility. It is much easier to find a high capacity battery of say 12V (a sealed lead acid or SLA) or 7.2V (a RC modelling racing pack) and then attach a cheap regulator (and waste a little of our precious capacity), than to find a perfect 3.7V source.

« Last Edit: 01 / September / 2013, 18:09:22 by ahull »

Re: ultra Low DropOut regulator and Buck/Boost for solar applications
« Reply #5 on: 01 / September / 2013, 19:25:11 »
It is much easier to find a high capacity battery of say 12V (a sealed lead acid or SLA) or 7.2V (a RC modelling racing pack) and then attach a cheap regulator (and waste a little of our precious capacity), than to find a perfect 3.7V source.

Which is what I do with the Pololu buck/boost converter and 6V SLA.

The converter will not reliably power my SX20is as the required voltage is near the end of the converters range, or maybe it is the inrush current.

For little more than the cost of the Pololu you can obtain on Ebay a larger, more capable converter.

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Offline bwh13

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Re: ultra Low DropOut regulator and Buck/Boost for solar applications
« Reply #6 on: 22 / April / 2014, 01:20:52 »
Hi All,

I wanted to post to share some of the results from the buck/boost and uLDO tests on my SD1000 running the Ultimate Intervalometer v1.7.  I was taking pics every 30 mins with a reboot everyday.

Buck/Boost
Great results with this unit from Pololu.  I set the output voltage to 3.8 and it never varied more than 3.9 or less than 3.84 over the course of the 17 days test. 
The trimmer pot. was a bit loosey goosey in terms of dialing in a specific voltage, but other than that, completely functional.  I'm glad I bought 2!

uLDO
I am 8 days in to this test and it is still running.  It cost about the same as the assembled Pololu regulator, but it uses a regulator with a really low dropout (ultra low!)  I forgot to write down what the output voltage was before I deployed, but will update this post in a week or so when I conclude the test.  This unit had a much more solid trimmer pot. so I could get my output voltage dialed a bit better.

 

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