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Thread: Has anyone built a boost - buck circuit?

  1. #1
    Maximum Bitrate starfox's Avatar
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    Has anyone built a boost - buck circuit?

    Was thinking earlier, if you had a Morex ATX power supply.. it would be possible to survive a crank if you had a boost / buck circuit.. it would also probably solve a lot of regulation problems which could fry your Morex PSU...

    eg:

    Car electrical system (13.8V) -> Boost (20V) -> Buck (12V) -> Morex PSU

    Something like a boost regulator to boost the car power rails to 20V or so, then buck to 12V to make a nice stable supply... Has anyone built one of these before, or found a reason why it wouldn't work?

    The Morex PSU power pack is rated at less than 5A, and National's simple switchers are rated to 5A... You'd probably need a lot of caps on the output though to handle the power on current surge..

  2. #2
    Raw Wave
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    Why not 8V > 16V > 12V?

    Then atleast you know you can operate from 8-16V and survive the crank

    I cant see it not working, the efficiency is gonna be less compared to a flyback design. Ill love to have a go but too busy with so many things right now


    Heck....I dont even need one, I just wanna build it out of interest

  3. #3
    FLAC robiewp's Avatar
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    I think his point was that a boost (step up) to 20v could be made not just from 13.8v but from lower voltages (thus hopefully surviving crank) and then buck (regulate) 12v.

    From what I understand, if you can find high enough amperage and tolerence boost and buck (I like those terms, never heard 'em before) circuitry, then this should work fine.
    car computer rev 5: 8" lilliput and usual suspects

  4. #4
    Raw Wave
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    I was just thinking its not that necessary to boost up to 20V.

    If boosting a 8V > 13.8V lets say then a linear regulator can be used to step down for simplified design such as the LM1084, or just use the ITPS for stepping down with the shutdown controller of course.

    I just hate those coils, not so easy to find them

    Some guys here use a laptop adaptor that boost from 11V to 15V or so...but 11V operating voltage wont survive a crank. An 8V operating voltage should be good

  5. #5
    Maximum Bitrate starfox's Avatar
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    my options are different as finding inductors for National's SMPS ICs is about as easy as sourcing a ITPS here

    The reason for suggesting 20V is that a buck has a greater efficiency if the voltage drop between the input and output are quite large. Bucking from 16V to 12V isn't going to be that efficient.. 20V to 12V isn't great either, but it's a little better.

    I don't particularly like linear regulators since once you use them your efficiency goes out the window!

    Though at the moment, i might be lucky as my setup doesn't seem to have any 12V devices at all (the motherboard doesn't seem to use the 12V line (!) and i don't have any 12V devices other than fans) and i've had the whole thing boot and run stable off a 10V supply...

  6. #6
    Maximum Bitrate starfox's Avatar
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    Also, i think boost controllers stop working if your supply voltage is greater than your output voltage, which might be the case if the supply voltages spikes above 16V..

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