Cheapest switching regulator configuration

Discussion in 'General Electronics Chat' started by stoopkid, Mar 6, 2012.

  1. stoopkid

    Thread Starter Member

    Mar 3, 2011
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    I'd like to replace my 7805 with a 5v out switching regulator. My inputs will likely not be outside of 7-12v and I certainly do not need more than 1 amp any time soon. So I'm wondering if I should go with an IC or use transistors to make the cheapest switching regulator possible. I'm hoping less than 2 or 3 dollars. A specific part number or schematic would really help me out.
    Thanks
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Cheapest would be a 555 timer and discrete driver cranking a cheap buck regulator, but it's not that easy. The easy way would be an LM2575.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,449
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    Find a 5V switching supply used to power consumer electronics. You can find them at electronic surplus stores or second hand stores for less than $5.
     
  4. stoopkid

    Thread Starter Member

    Mar 3, 2011
    136
    1
    Ill go with the LM2575... Thanks!
     
  5. debjit625

    Well-Known Member

    Apr 17, 2010
    790
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    The cheapest switch regulator as per me is MC34063A.Its a 1.5 A, Step-Up/Down/Inverting Switching Regulators.

    Good Luck
     
  6. stoopkid

    Thread Starter Member

    Mar 3, 2011
    136
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    MC34063A looks a bit more complicated but Ill keep it in mind for the future... Thanks!
     
  7. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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  8. panic mode

    Senior Member

    Oct 10, 2011
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    Last edited: Mar 9, 2012
  9. stoopkid

    Thread Starter Member

    Mar 3, 2011
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    This is pretty cool, I might give it a try too.. Thanks.
     
  10. panic mode

    Senior Member

    Oct 10, 2011
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    Question for THE_RB:

    I don't expect LDO but this looks so simple and neat, it got me curious. Did you try it at different supply voltages? What is reasonable range?

    regards

    PM
     
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Yep it works for a wide range, and that is one of its big advantages with the right Q1 transistor you can use it for a higher voltage input like 60v or 70v in 5v out, a range very hard to find in cheap SMPS chips.

    Resistor choices are important if you change the input voltage range especially if you want to keep efficiency quite high. For that reason it's not a great SMPS where the input voltage varies within a large range. However that can be fixed easily enough by adding a 3rd transistor to keep Q1 base current constant (when on).

    People have built the 2 transistor version to work from 110v mains input (170v DC) with the right resistors and a high voltage Q1. However I won't publish details of a 170v version due to forum regulations and safety issues. If someone is a professional who is allowed to work with mains equipment then they are capable of working out the parts values themselves. AND even then it means that every part of the circuit would be considered live at mains potential and possibly lethal. So don't do it.
     
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