Voltage regulator options

Discussion in 'The Projects Forum' started by Cmpenney, Dec 9, 2014.

  1. Cmpenney

    Thread Starter New Member

    Dec 9, 2014
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    I'm working on a project to build a bunch of modules that will control addressable LED strips over a decent distance using a 4 wire bus where two of the wires are supplying 12v power and two wires are used for a RS485 bus. The LED strips and transceiver ICs run at 5v so I need to step my voltage down at each module. In my testing circuits I've been using 7805 VRs but because each module can draw over .5 amp I'm worried about heat issues. The modules need to be small to fit in their final locations so I don't have a lot of room for a large heat sink. So I'm trying to find a non-linear option to reduce heat issues that is of relatively in expensive due to the number of these I need to build and small due to the space limits.

    At present I'm looking at the MC34167TG as a possible solution but I've never used these before and haven't been able to find any real examples of others using them for projects. has anyone used these in a project before and could provide some feedback or possibly suggest another option for this application?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    I haven't used that part but it look like a relatively simple way to use an efficient switching regulator to drop the voltage to the LEDs. Just make sure you follow the proper decoupling and layout rules as indicated on page 8 of the ON Semiconductor data sheet.
     
  3. Cmpenney

    Thread Starter New Member

    Dec 9, 2014
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    Didn't notice the note about not using a bread board to prototype the circuits... That kinda stinks.

    I'm wondering if maybe a LM2576 would be a better option? It appears that there are a few mentions of using them in projects around the net.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    Maybe or maybe not. Virtually all switching regulator chips will warn you about breadboard construction. Those warnings are mostly about the inductance and resistance of high current paths. If you keep the connections short and employ Manhattan style dead bug construction you may be able to get away with it.

    http://www.qrpme.com/docs/K7QO Manhattan.pdf
    https://www.google.com/search?q=Man...in%2Fforum%2Fviewtopic.php%3Ft%3D1436;575;416
     
  5. Cmpenney

    Thread Starter New Member

    Dec 9, 2014
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    Grrr... As I'm digging into these more and more the need for a decent size inductor plus other components required to support these is starting to make them look less and less like an improvement over the 7805 for my application. By the time I add these extra components I really woudn't have saved any space and will surely have increased the cost. Due the higher current rated members of the 7805 family produce less heat at the same current draw?

    With all the other hurdles of this project that I thought would be issues it's surprising that finding the right voltage regulator solution turns out to be the thing that has me stuck.
     
  6. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Last edited: Dec 9, 2014
  7. Papabravo

    Expert

    Feb 24, 2006
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    The sheer variety of available options forces the designer to think through and clearly articulate the requirements. Tradeoffs made at this stage have an enormous impact on the final result. Inability to go through the process causes you behave as in the following piece of doggeral:

    When in trouble,
    Or in doubt;
    Run in circles
    Scream and Shout.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    The current rating of a linear regulator has no relation to the power it will dissipate in a given circuit. The power dissipated is always the current times the voltage drop across the regulator from input to output.
     
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    If you must start with a 12V supply, then the power dissipated in each module could be reduced by supplying each module from, say, an 8V bus instead of 12V, and using a single heavy-duty 8V pre-regulator driven from the 12V supply.
     
  10. rsjsouza

    New Member

    Apr 21, 2014
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    The closest to breadboarding is something Afrotechmods shows in this video (edited - I linked the wrong video before) - jump to 6:00 for the construction.

    You can also check the higher current linear options, such as LM1084 and LM1085.
     
  11. Cmpenney

    Thread Starter New Member

    Dec 9, 2014
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    This would be a perfect option were it not for the cost. I'm came across these: http://www.digikey.com/product-deta...2619294-VQ2-g-VQ6-53968144515-VQ15-1t1-VQ16-c which is a similar product but even more economical. Since I have to build 15 of these the price adds up really fast. Otherwise it would seem this is the perfect solution to my problem. Low heat and compact.

    I'm using a 12V bus because of the distance involved. These modules are going to be spread out on stone columns along a fence row that is about 95 ft long( 140ft cable ft). Otherwise I'd just get a good 5V powersupply to run the whole thing. Your suggestion is along the lines of what I'm looking into now though. Using a resister before the regulator to drop the voltage a bit before it hits the regulator. I know that the overall heat generated will still be the same but by having some of the load handled by the resistor.
     
  12. Brevor

    Active Member

    Apr 9, 2011
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    Can you power the led strips from the 12 Volts and use a 7805 (or 78L05) to power just the microcontroller?
     
  13. takao21203

    Distinguished Member

    Apr 28, 2012
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    DSC02840.jpg
    these are small
     
  14. Cmpenney

    Thread Starter New Member

    Dec 9, 2014
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    Unfortunelty no, each module uses one of the NeoPixel Sticks https://www.adafruit.com/product/1426 which requires 5v and it's the sticks that use the vast majority of the current.
     
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