Wide Range Voltage Regulator

Discussion in 'General Electronics Chat' started by TPrather302, Jun 12, 2012.

  1. TPrather302

    Thread Starter New Member

    Jun 12, 2012
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    Hey guys! First post, but I've got an issue that I've been struggling with and I think it's finally time to ask for help.

    I have a variable source from 2-28V and I need an output of 5V. I've looked all over digi-key and mouser for something that would work for this, but I'm not coming up with anything in that range.

    I found a Linear regulator that works beween 8-30V and outputs 5V. Could I use that, and then a boost transformer after that so that the voltages between
    2-8V would be boosted up to 5V?

    Thanks for the help!
     
    Last edited: Jun 12, 2012
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    required current at 5V?

    you can find buck-boost chips or inductor sepic circuits but going down to 2V is a little tough.. How about 3V as the min..

    What is this "source"?
     
    Last edited: Jun 12, 2012
  3. TPrather302

    Thread Starter New Member

    Jun 12, 2012
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    Not a hard limit, but 1A would be great. 500mA is about the minimum.
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Impossible. I think it would require a sepic or buck-boost to handle that range of input but you won't find any circuits that boost from 2V input.
     
  5. panic mode

    Senior Member

    Oct 10, 2011
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    you can use this to drop 7-36 volts to 5V. unlike linear regulator this one does not need any heatsink even when you use max imput voltage and draw 1.5A from it.
    http://www.mouser.com/ProductDetail...RT2lXVNWg5/3Kq428yVOxYAdOa2G8Z2a%2bF%2b/5ymI=

    there are also step up regulators but expecting to use 2V is unreasonable or let's say challenging.
    for example low input step up converters like tps61221 exist, but you will never find universal switcher that can operate both as step down and step up regulator because configuration changes.
    either you have input range that is below output voltage (all the time) or
    you have inout range that is above output voltage (all the time).
     
    Last edited: Jun 12, 2012
  6. #12

    Expert

    Nov 30, 2010
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    That one requires 7 volts minimum.
     
  7. panic mode

    Senior Member

    Oct 10, 2011
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    eh ?

    yes and i mentioned it (7-36V). also it beats the linear regulator he found.
    all regulators will have range. i am not aware of one that will do entire range he is asking for...;)
     
  8. MrChips

    Moderator

    Oct 2, 2009
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  9. panic mode

    Senior Member

    Oct 10, 2011
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    yes, but will it provide regulated 5V, and supply 1A?
    also will it work over 2-30V range he is asking?

    chips like tps61221 can boost voltage and provide regulated output that can drive significant current, but they also don't cover entire voltage range.

    for 5V output and 2-30V input there is need for different solutions. at least i am not aware of single one that will cover entire range.
     
  10. JMac3108

    Active Member

    Aug 16, 2010
    349
    66
    Couple comments....

    Often, wide input range PS requirements are handled exactly as the OP suggested. With a boost on the front end to compress the range. When the input is above the voltage of the boost regulator, it just becomes a pass-through.

    Take a look at Linear Tech boosts. I don't remember the part number, but they have boosts that go down to 2V. They can go even lower once running because they use the output to generate the internal VCC for the chip. I've used them to boost a single NiCd cell to 4.8V.
     
  11. TPrather302

    Thread Starter New Member

    Jun 12, 2012
    3
    0
    Hey guys,

    I was off for a week, but I thought I would give an update as to what solved my problem.

    I have a circuit now that is regulating between 1.5-30V to 5V with a max of 2A current. To do this, I used a LD1085, then a LM2623 and I have a solid 5V coming out of the LM2623 from the voltage range between 1.5-30. :D

    The only weird part is that the LM2623 seems to pull about 2.5A for a brief second at startup. Is this normal or is something going on?

    Also, if you see any long-term reliability problems with this, please let me know what you think!

    Thanks!
     
  12. #12

    Expert

    Nov 30, 2010
    16,261
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    Judging by your schematic, you should be all right with this one, and I thank you for informing us of a soultion that was not easy to find.

    That was a very slick move finding a step-up that would work down to .8 volts and using a step down that would survive 30 volts. Even though the LD1085 (step-down) won't work at 2 volts, it will pass .9 volts to the step-up chip and that is enough!
     
    Last edited: Jun 25, 2012
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