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Single power supply for 2 devices

Discussion in 'Power Electronics' started by eob2000, Jun 14, 2015.

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  1. eob2000

    eob2000

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    Jun 14, 2015
    I have 2 DC powered devices that have their own AC adapters. I want to use them in a project together but want only one power connector. The first device is 12V 1.5A and the second device is 5V 2A, I want to power the project with an external power supply, I thought a laptop charger but the one I have is only rated for 3.34A. I am very new to electronics, I assume that my 19.5V 3.34A power supply cannot power 17V 3.5A, Please correct me if i'm wrong. Regardless please can someone tell me how to achieve this split output (Even if I need a new supply)

    Thank You
     
  2. davenn

    davenn Moderator

    13,672
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    Sep 5, 2009
    hi there eob2000

    yes, you are not correct ... a few problems with your understandings there

    OK that's good ... so you need to create those 2 voltages from a single input that's higher than the largest of those 2

    the 12 and 5 DONT add so it's not 17V you need ... see my first comment

    you can use the 19V 3.34A laptop supply at a pinch preferably you really need a 5A one to get some headroom

    this is the sort of thing you require ....
    http://www.ebay.com.au/itm/DC-DC-Ad...9cc6d&pid=100338&rk=18&rkt=29&sd=251730814512

    from your 19V supply, you need 2 of them, one set to 12V and one set to 5V

    the other way is to get a 12V 5A PSU and supply the 12V device from that and from the 12V line use just one of those buck converters to produce the 5V line

    Dave
     
  3. davenn

    davenn Moderator

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    Sep 5, 2009
    an extra comment on current requirements ....

    current requirements DO add, ....

    ohhhh ..... before I get into that ..... is the text on the devices plugpacks say 12V 1.7A and 5V 2A or is that what is stated on the devices themselves ? this is important


    if it's what is on the devices then you have 2A and 1.7 A and that adds to 3.7A and your laptop supply is 3.34A max
    do you see a problem ?
    That's why I said earlier that you need a 5A capable supply

    Dave
     
  4. eob2000

    eob2000

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    Jun 14, 2015
    The info is from the plugbacks, unfortunately neither device has and power requirements. printed on them

    One of the devices is a IDE-USB unit being used to connect a HDD (the 12V device)

    The other is a powered USB hub, I am powering various things including a raspberry Pi so I believe I will need the full current (the 5V device)
     
  5. davenn

    davenn Moderator

    13,672
    1,891
    Sep 5, 2009
    OK that is probably an advantage to you as those will be the maximum ratings for the 2 PSU's
    meaning that the current drawn from them is likely to be a bit lower

    Give the 19V 3.34A laptop supply a go with 2 of those buck converters from eBay and see how you go :)

    Dave
     
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