[TriEmbed] Power Questions

Thu Oct 24 11:46:46 CDT 2013

Linear makes great ICs. One problem is that it doesn't look like that comes in a DIP package, which Chip specified as one of his design parameters. In fact, it doesn't look like Linear makes any through-hole switching regulators! I have been interested in putting together a buck-boost circuit design for a while, this was a good excuse for me to look around a bit.

This made it very easy: http://www.digikey.com/catalog/en/partgroup/buck-boost-ic/14421

You can page through the various manufacturers. Sort by Package / Case to find DIP (through-hole) ICs if you need them. it looks like the *3046* ICs are the most prevalent for what you are looking to do, all the major manufacturers have them:

http://www.digikey.com/product-search/en?mpart=MC33063AP&vendor=296
http://www.digikey.com/product-search/en?mpart=MC34063ACN&vendor=497
http://www.digikey.com/product-search/en?mpart=KA34063A&vendor=261

This LM2578A looked like it would fit the bill, as well. There are application notes for the buck-boost configuration in the datasheet: http://www.digikey.com/product-search/en?mpart=LM2578AN%2FNOPB&vendor=296

More application notes for designing one of these circuits with a *3046* IC:

http://www.onsemi.com/pub_link/Collateral/AN920-D.PDF
http://ace.ucv.ro/sintes12/SINTES12_2005/ELECTRONICS/E1.PDF
http://ace.ucv.ro/sintes12/SINTES12_2005/ELECTRONICS/E2.PDF

Keep in mind it's not as simple as throwing an IC into your circuit with these guys. They require some additional components and knowledge to use.

- Adam

On Oct 24, 2013, at 11:36 AM, Jim Carlson <jbcarlso at ncsu.edu> wrote:

> I have used two circuits for several years. The first is a buck-boost from Linear Technologies. LTC3531. This is relatively efficient, and operates from an input of 1.8v to 5.5v. Thus you can use it with several battery combinations. I have used it with 4 "AA" as they rapidly discharge down to the 1.35 range and the margin in the device will tolerate the over voltage condition. I have also used it with to 2 "AAA".
> 
> If you want to add in a Li-Ion cell, I would suggest you use the Linear Tech LTC4055. This will allow for recharge from either a USB or wall wart. The output from this device feeds the LTC3531.
> 
> If interested in either of these solutions I have some personal boards laid out to use them.
> 
> Jim Carlson
> 
> 
> On Thu, Oct 24, 2013 at 11:07 AM, John Vaughters <jvaughters04 at yahoo.com> wrote:
> Chip,
> 
> That is some mighty impressive work there. The woods around the Airport would be great for bike trails. I will make a suggestion, but it is completely untested, so I would be curious to your results. I have often used Buck regulators from old car Cell phone chargers to pull power for 5 volt electronics in cars. Just about everyone has 5-10 laying around the house alone. You can break them open and reduce the space by taking out the electronics. They are basically designed to provide 5-6V from a 12-18V source. So you could see what they provide with 9V first, but if that doesn't cut it, use two 9V for an 18V source. I still use a 7805 to get it to 5V, I prefer to prevent over voltage from the Buck. 
> 
> This may or may not help you, but the cost is really cheap. Walmart even sells them for about $5. The main problem is that these buck regulators are not the most efficient and they get worse as the difference in voltage between source and sink rise. 
> 
> If you go this route, let us know how it works out for you.
> 
> Thanks,
> 
> John Vaughters
> 
> 
> On Thursday, October 24, 2013 10:24 AM, Charles McClelland <chip at mcclellands.org> wrote:
> First, 
> 
> I want to thank you all for the help I have received so far.  I am working with a group that is building and maintaining trails in the woods around the RDU airport.  We are talking to the state and county parks folks and need some solid data on trail utilization to support your requests.  I am building a simple sensor to count the bike traffic per hour on a trail in the woods over a week.  
> 
> Thanks for Paul’s suggestion, I went with a Piezo sensor attached to the underside of a wooden bridge and write the counts every 3.6M clock cycles to EEPROM.  Each count takes just one byte (never more than 253 bikes in an hour) so the setup should last for 21 days before taking up all 512 Bytes of memory.  I tested it last weekend and it worked like a charm - here are some pics and a short clip of the sensor in action.  
> 
> Now the problem and a request for help.  I am currently using a 9V battery (typical capacity 310 mAH) and a 7805 linear regulator.  With a fresh battery, I am only getting about 24 hours of operation.  I have some high capacity 18650 LiON batteries which operate at 3.6 volts (voltage curve here).   Which I can put in series using a simple holder.  The problem is that I will not get nearly the full capacity of the batteries (3400 mAH each) before I am below the drop-out voltage of the 7805.  At the PCB Carolinas conference yesterday - I asked around and was delighted to hear about a “high efficiency buck boost regulator” like this one.  However, I can’t seem to find one in a through-hold package.  
> 
> I also considered putting a diode in series with the 18650 batteries to knock off a volt.  However,  looking at the voltage curves, it seems that I would exceed the 6V maximum the Atmel data sheet specifies for the ATtiny84 when the batteries are freshly charged.
> 
> I want to keep this circuit cheap and small as it will be buried in the dirt for a week at a time and may well get stolen.  Any suggestions would be appreciated.
> 
> Thanks, Chip
> 
> PS - thank you for the PCB Carolina’s suggestion - made some great connections to local suppliers and enjoyed the free food.
> 
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> 
> -- 
> Thanks,
> Jim Carlson
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