12V / 6A power supply design. Help with Buck and Boost converters

Discussion in 'The Projects Forum' started by esm., Jun 7, 2012.

  1. esm.

    Thread Starter Member

    Jan 20, 2012
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    0
    Hello all.
    Maybe someone here can give me suggestion of ICs and make considerations about this design.
    The picture below states how this power supply should work.

    [​IMG]


    DETAILS:

    1) IC 1 probably will be a LT3650-8.4 from Linear Technology. It supports up to 32V of input voltage (40V peak). Suggestions of other ICs for this purpose?

    2) The power supply INPUT has only two states: (A) Floating (cut-off) and (B) 17 to 30VDC present at the input.

    3) The OR'ing circuit at the OUTPUT, as the picture shows, doesn't mean it will be done with diodes. It can be done with MOSFETs, relays, or any kind of logic control like, for example: When the INPUT is connected to a 17 to 30VDC PSU, a logic LOW is present in an ENABLE pin of the BOOST converter, so that this remains in idle state (Output in high impedance). When there is no power supply connected at the INPUT, the same ENABLE pin goes logic HIGH, so the BOOST converter goes to active mode and presents 12V at its output.

    4) The intention of using batteries is, case the INPUT be floating, maintain the circuit connected to the 12V OUTPUT working for at least 10 minutes (If more, better), through the BOOST converter

    5) Which BUCK and BOOST controllers could I use for this design (IC 2 and IC 3)?

    6) How can I do the Or'ing circuit between Buck and Boost controllers? Some suggestions?

    7) There are no restrictions if heatsinks are required. No restrictions with the final physical dimensions of the PCB. Just need to work.

    8) No problem if external MOSFETs are required, both on Buck and Boost converters

    9) Final cost of this PSU is not so important.

    10) Preference to SMD packages in all the circuit, if possible.

    11) The 12V OUTPUT can be designed to deliver more than 6A. No problem about that.

    12) No need of insulation (Flyback / forward topology, for example). The topology can be modified to Flyback / Forward also

    Maybe a Power supply like this already exist in the market (a final product I mean), meeting this specifications, or even better than, ready to use. I did some research about but didn't found any models.

    For the time, all I found is a Buck converter from Linear Technology, based on a LTC1624. Example of a 12V x 10A output with Vin range of 13 to 28V using this converter:


    [​IMG]


    Somebody help me ?
    Thanks in advance.
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    You have a Li-Ion charger that you you are feeding 17V - 30V to that IC?

    IMHO, you need to state the circuit objectives and rethink that design. Getting a 12V/6A bossted from a 6V line is going to take some harware. With the battery, you would be lucky to get 15 minutes run time.
     
    Last edited: Jun 7, 2012
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  3. esm.

    Thread Starter Member

    Jan 20, 2012
    30
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    I can do a hardware to stop the boost converter when the battery voltage is lower than a determinated value, 7V eg. The battery problem I can solve later, but first I want to make this power supply work without baterry.

    My main question is about which buck and boost controllers I can use for that?
    Somebody here have used some controller that can meet the parameters?
     
  4. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I recommend using a four cell series stack to get enough voltage so you don't need a boost.
     
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  5. ronv

    AAC Fanatic!

    Nov 12, 2008
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  6. esm.

    Thread Starter Member

    Jan 20, 2012
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    i would like to ask the users from the forum if they already used such kind of controllers, a particular buck or boost IC, similar to the ones I would need to meet the requirements of my circuit, and if the results were satisfactory.

    its always good to hear from someone who tested an IC in practice and how were the results. I am trying to get some recommendations.
     
    Last edited: Jun 9, 2012
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    I have used many such IC controllers, in fact when I worked at NSC, I developed a few. They work well but are not for novices because the PCB layout is critical to get them to work right. You might pick a IC and then contact the company (like Maxim, Linear Technology or national Semi) and see if they have a demo board available which are typically offered for a modest price. You can customize the board to meet your needs.
     
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  8. esm.

    Thread Starter Member

    Jan 20, 2012
    30
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    I was rethinking about this design.
    The output current will be reduced to 4A at the maximum load, not 6A as the initial idea
    I think now I can have a single solution based on a buck-boost topology, right?
    My only experience with a buck boost IC was the TPS63000 from Texas, but it doesnt fit the requirements of this design.
    Some other recomendations of buck boost ICs now?

    Best regards
     
  9. esm.

    Thread Starter Member

    Jan 20, 2012
    30
    0
    Hi.
    Have somebody ever seen a single Li-ion charger IC, capable of charging 4 Li-Ion cells connected in series? In a single chip?
    I was really thinking to use 4-cells, but which controllers to use? Didn't found any.
     
  10. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    TL494 is a good IC for this.

    I have built a circuit here powering a 12V 50W bulb, using a LM2576 + external MOSFET. There are some issues to start up these, current is very high, finally I solved it using a voltage foldback resistor.

    At 10 Amps you will get serious cooling issues and smaller coils can't be used anymore, you need a larger one, which is suitable, otherwise current+heat will go up too much.

    TL494 frequency can be adjusted so it's better than fixed frequency ICs, in my opinion.

    There are ready-made converter modules on eBay for good price to boost 12V to 35V, but logically, if you want to use buck/boost together, both should be identical for components. These use the UC3843, not as easy to use as TL494: http://www.ti.com/lit/ds/symlink/uc3843.pdf

    TL494 can be used for buck or boost, but I don't think one IC together for both, there is a technology called CUK converter but I never tried this myself. Depending on the on/off modulation, it could be used for buck/boost together, as far as I understand.
     
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