3.3V Regulator Options?

Discussion in 'General Electronics Chat' started by NFA Fabrication, Aug 17, 2012.

  1. NFA Fabrication

    Thread Starter Member

    Aug 12, 2012
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    I am in need of a 3.3V regulator, the simpler the better. I am hoping to find something in a 220 case like a 7805 5V unit. I purchased these from digikey:

    http://www.digikey.com/product-detail/en/LM2937ET-3.3/NOPB/LM2937ET-3.3-ND/363870

    But they require a capacitor on the inlet and outlet, and the unit gets really hot. The 7805 (5V), and 7812 (12) from radio shack seem to work fine with no capacitors, and do not get hot with a reasonable load. Is there a 3.3V equivalent to the 7805/12? This is mainly for LED voltage regulation in RC model planes, and I'd like to avoid having a resister on every LED. Thanks for any assistance! First time poster, long time lurker!

    Edit, I am OK with having to add the capacitors if there is no way around this, but something that does not generate so much heat would solve most of my issues! Also, I will be using this on 4 cell lithium batteries, so the nominal voltage is 14.8V, but at full charge no load, they can be near 17V.
     
    Last edited: Aug 17, 2012
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Leds are current controlled devices.
    When you are using a voltage regulator to drive the leds, the currents on the leds may be very different.

    Read this thread made by Bill_Marsden:
    LEDs, 555s, Flashers, and Light Chasers

    Bertus
     
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Nearly all linear regs need input and output caps.
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    The reg has nothing to do with the heat, that is a function of power dissipation. Any linear reg you drop in will have the same power diss. You would need a switcher to reduce that.
     
    #12 likes this.
  5. Papabravo

    Expert

    Feb 24, 2006
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    Or a big aluminum heatsink. Hang the fins out in the relative wind and the airflow should keep the regulator as cool as a frosty mug of root beer.
     
  6. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    You need a method to provide the LED's with the proper current to operate.. A regulator does NOT do that...a resistor does.
    In this situation the simplest method IS using resistors..
     
  7. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    That's where the heat is coming from. If you can reduce the voltage into the regulator, it will have less power to dissipate in the form of heat. And I suppose you realize that your batteries wouldn't run down as fast.

    The best solution is to run your LED's on the battery voltage. If they are all rated for the same voltage drop and current, you could arrange them in groups in series to reduce the number of resistors required. How many LED's are there, what color are they, what current do they require to light them, and can they be grouped (or does each one have to turn on and off independently?)
     
  8. NFA Fabrication

    Thread Starter Member

    Aug 12, 2012
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    Sorry, a bit of a newb, dare I ask what a switcher is/does?
     
  9. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    There are basically two types of voltage regulators: linear regulators (like the LM7805, etc.) and switching regulators. Linear regulators are much less efficient than switching regulators (and therefore have to dissipate more heat), but also simpler to build.

    When bountyhunter says, "Any linear reg you drop in will have the same power diss," he means that any linear regulator of a given voltage will have the same voltage to drop and therefore the same power dissipation.
     
  10. #12

    Expert

    Nov 30, 2010
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    P=IE (power = current times voltage)
    14.8 volts - 3.3 volts = 11.5 volts.
    11.5 volts times whatever current you use will be the wattage (heat) on every linear regulator chip ever made.

    The idea about grouping LEDS to get some series strings going is good. That saves quite a bit of current, which is directly translatable to heat.

    The idea of using a switching regulator is good, too. There are some websites that provide all the math and make this kind of circuit very do-able. It's way more efficient (less hot) than linear regulators.

    ps, I know I'm just repeating a lot of what other people said.
     
  11. ramancini8

    Member

    Jul 18, 2012
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    The reg has nothing to do with the heat, that is a function of power dissipation. Any linear reg you drop in will have the same power diss. You would need a switcher to reduce that.
    This statement is not correct. A 12 volt regulator will dissipate less power than a 3.3 volt regulator because the majority of the 12 volt power is dissipated in the load. Small point, but many newbies are on this site. A resistor in series with the led makes it current driven and a string of leds will be approximately the same brightness, while one led can can be extra bright and hog the majority of the current whem voltage driven.
     
  12. #12

    Expert

    Nov 30, 2010
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    True. If you change the title of this thread, change the voltage you want, and change the voltage on the regulator chip you buy, the amount of waste heat would be different.
     
  13. NFA Fabrication

    Thread Starter Member

    Aug 12, 2012
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    Thanks for the replies! I usually run anywhere from 10-20 clear led's rated for 24ma each. I have also done series and parallel set-ups, but often get one or two dim LED's when doing that as they very slightly per LED. I built a regulator using an LM317T before, and it worked great, but was just trying to see if there was a less bulky method. If the heat I am getting from the regulator I have now isn't doing any damage, it really isn't an issue, and I can put it on a heatsink just inside the planes cowl to get inlet air from the prop. With adding so many LED's it isn't practical to add a resister for each LED.
     
  14. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I responded correctly to his post:

    He was under the incorrect assumption that getting a different "kind" of linear regulator, ie a radio Shack version reduces heating. It can't. Any linear regulator placed into the same input voltage, output voltage and load current dissipates the same power.

    The frying 3.3V reg is due to voltage drop and load current and getting a "7805 equivalent" will avail him absolutely nothing.
     
    Last edited: Aug 18, 2012
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