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Thread: buck converter sizing

  1. #11
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    Default Re: buck converter sizing

    Quote Originally Posted by WayneKremer View Post
    I like ProDCtoDC, but their shipping is outrageous. For 15 converters, they want $40 to ship to me in Nevada. Because they are based out of China?
    All looks like the regular asian products, why use them as a vendor?

  2. #12
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    Default Re: buck converter sizing

    Is the amperage rating of buck DC to DC converters the input amperage or the output amperage?

  3. #13
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    Default Re: buck converter sizing

    Ouput
    Of course, it can't produce more amps than are input. It only changes the voltage.
    Quote Originally Posted by scott4864 View Post
    Is the amperage rating of buck DC to DC converters the input amperage or the output amperage?

  4. #14
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    Default Re: buck converter sizing

    Quote Originally Posted by WayneKremer View Post
    I like ProDCtoDC, but their shipping is outrageous. For 15 converters, they want $40 to ship to me in Nevada. Because they are based out of China?
    I email them directly and ask for a quote.. shipping is cheaper that way.. but still not low cost.. adds about $1.50 to $2 per converter.. but still cheaper than Amazon.. and I wouldn't buy any of that stuff off of ebay.. been burned too many time with ebay and Chinese "stuff"...

  5. #15
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    Default Re: buck converter sizing

    Quote Originally Posted by ukewarrior View Post
    Ouput
    Of course, it can't produce more amps than are input. It only changes the voltage.
    Well.... I'm pretty sure you didn't mean it the way you wrote it. For example, if you use 24v input and 12v output, the input current will be a bit over half the output current.

  6. #16
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    Default Re: buck converter sizing

    Quote Originally Posted by scott4864 View Post
    Is the amperage rating of buck DC to DC converters the input amperage or the output amperage?
    Most are specked using output current since the output winding on the transformer and the bridge rectifier are the gating items. Specking input current means you can control the efficiency to a very tight tolerance.


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  7. #17
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    Default Re: buck converter sizing

    Duh on my part. Correct
    Quote Originally Posted by plasmadrive View Post
    Well.... I'm pretty sure you didn't mean it the way you wrote it. For example, if you use 24v input and 12v output, the input current will be a bit over half the output current.

  8. #18
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    Default Re: buck converter sizing

    The better view is "power transfer", minus some power loss, then the voltages or currents can be "re-arranged" to match the output power.
    Last edited by LightUp; 09-04-2017 at 09:28 AM.

  9. #19
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    Default Re: buck converter sizing

    Look at it this way: For a DC-to-DC converter

    Input voltage = 12v
    Output voltage = 5v
    Conversion efficiency = 90%

    Load "Power" is 10W
    Load current = load power / load voltage
    That means load current = 10W / 5V = 2A

    Input power = output power / conversion efficiency / 100
    Input Power = 10W / .90 = 11.11W
    Input current = Input power / input Voltage
    Input current = 11.11W / 12V = 0.926A

    Where does that extra power go? It is dissipated as heat. The loss is 1.11W

    For a voltage regulator (Like you find in 12v pixels and in some devices that call themselves converters)
    Input voltage = 12v
    Output voltage = 5v
    Load "Power" is 10W
    Load current = load power / load voltage
    In our example load current = 10W / 5V = 2A
    Input current = output current = 2A (this is the big difference in the calculations)
    Input power = Input Voltage * Input current
    Input power = 12V * 2A = 24W

    Where does that extra power go? It is dissipated as heat. The loss is 14W
    Last edited by MartinMueller2003; 09-10-2017 at 12:00 PM.


    2019 - Just moved into a new home (yet another change of plans). Will be dim but not dark. Too much to do at the new place to leave time for a show.
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  11. #20
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    Default Re: buck converter sizing

    And thus why those of us that design power supplies are always looking at increasing the efficiencies to eliminate heat and wasted power. Martins excellent explanation also shows why its better to use a switching regulator over a linear.

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