Switching supply topology

Discussion in 'General Electronics Chat' started by eblc1388, Mar 29, 2009.

  1. eblc1388

    Thread Starter Senior Member

    Nov 28, 2008
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    Hi,

    Is there a configuration that would produce a constant output voltage with input voltage ranging from below to over the desired output voltage?

    E.g. A 5V output voltage for 3~10V input voltage.

    Links on info or schematic examples welcome.

    Thanks.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    The topology that you are referring to is a referred to as a buck-boost mode smps.

    hgmjr
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Your description is of a "Buck/Boost" Switching Power supply. They are available in IC format, or as discrete circuits, but not a quick and easy circuit to design and build, compared to a linear regulator.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    National Semiconductor has a design tool on its web site for its "simple switcher" series. I don't have the links handy. You will find a lot of chips numbered like LM2679; be sure to look at the LM22679, etc. chips as well.

    John
     
  5. eblc1388

    Thread Starter Senior Member

    Nov 28, 2008
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    Thanks thatoneguy and hgmjr. The configuration is indeed "buck-boost" and with that term google search turns up quite a lot of interesting information.

    There is one by TI called tpic74100-q1 which provides +5V output for 1.5V to 40V input voltage. The link of the datasheet is here:

    http://focus.ti.com/lit/ds/symlink/tpic74100-q1.pdf

    A study of the IC internal reveals that MOS switches were used to switch the inductor connecting position to achieve either buck or boost configuration, depending on input reaching a crossover voltage. Interesting IC.

    [​IMG]


    @jpanhalt,

    The LM2679 and LM22679 appears to be a buck(Step down) converter IC only.
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I understood that the part numbers I gave were for buck regulators. I gave them to illustrate that National is adding a 2 to many of its regulator products for newer versions. I did not have access to my files at the time to find a better example.

    Another comment re. National: Its WEBENCH can be helpful in addition to its design tool. I used WEBENCH to get some parts I did not have and could not meet the minimum at DigiKey for ordering. It may be a little more expensive for some items, but not outrageous. They shipped fast and appeared to be in DigiKey packaging. I suspect that WEBENCH creates design-specific orders and DigiKey fulfills them, at least in the USA.

    I think it is worth checking out, but of course, TI is pretty good too.

    John
     
  7. eblc1388

    Thread Starter Senior Member

    Nov 28, 2008
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    Thanks for the pointer John.

    It appears that it will not be easy to rig up a circuit with discrete component because a mode change in the configuration topology is required.

    I think using those special ICs which incorporate the mode switching hardware internally or with signal pins for external MOSFETs connection would be a much easier solution.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    I'd be interested in a step up SMPS
     
  9. eblc1388

    Thread Starter Senior Member

    Nov 28, 2008
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    Hi Bill,

    The boost topology of a SMPS produces an output voltage higher than the input voltage. It is not much different to the usual "Buck" type SMPS except in the way the inductor and the On/Off control switch is connected.

    Can you elaborate a bit more on your comment?
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    It's funny, I'd never heard the term "buck" until I joined this site. I have plenty experience with SMPS, and studied them in college, but I don't think the term had been invented yet.
     
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