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DIY 5v, 2A tablet dc-dc charger for car??

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  • DIY 5v, 2A tablet dc-dc charger for car??

    hello guys. i have a tablet, that has external DC source. at the AC/DC transformer it says : outpout 5v 2A..
    so i want to make a dc-dc converter, to power the laptop in the car. My consern is this, will ANY 5v source do? or will i do a specific circuit, to give constant 2A?? (i really dont know how this thigns work...)
    the reason i ask, is, its a bit hard to find a ready car charger (that dosent use the usb port)..

    if just 5v, are enough, i was thinking to just use 5v Voltage regulators, becouse i want to avoid the switching power supply noise... anything i should look out for , here?
    Last edited by settra; 11-08-2013, 06:22 AM.

  • #2
    IMO there are times you don't make sense...
    If you had a 5V source, you wouldn't need a regulator (assuming that 5V source can provide 2A).

    You could use a linear reg - they are available with 3A outputs else can be boosted with 2N3055 (or TIP2955 etc) transistors - but IMO why use all that volume and generate all that heat?

    I'd use a switcher - only crap designs have noise issues.
    And there are some nice HF designs (>1MHz) which apart from being so much smaller, IMO should be very difficult to emanate noise - eg eBay 360741066304.
    Otherwise the classic ~50kHz LM2577 else newer 400kHz XL6009 designs.

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    • #3
      Originally posted by OldSpark View Post
      IMO there are times you don't make sense...
      lol :P . what i want in mind is as simple as it gets. get the unregulated 12v from car battery, and use an 5v voltage regulator (and by that i mean , a linear regulator) and just hook that 5v to the tablet DC input!.
      ofc i could also use a switcher. but my question would be the same . if i would need an ampere source as well as a voltage source. but from your answer, i assume, just hooking 5v to the tablet (etc if there existed a 5v battery) , will charge it. correct?

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      • #4
        "i would need an ampere source as well as a voltage source" - I think that is your problem....

        You need a 5V power source (converters, regulators, etc) that is capable of delivering 2A (or more).
        So a 78S05 or LT1085 (set to 5V) or their low current 7805 or LM317 version with transistor current boosters.

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        • #5
          Just make sure your circuit is designed to handle Automotive voltages. Some Regulators are designed for in car use and others are not. You can also add protection circuits to your regulator to protect it from over voltages, spikes and other nasty things that can happen in your car.

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          • #6
            cool. do you have any kind of such protection circuit in mind??

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            • #7
              I am sure you could get away with this little gem http://uk.farnell.com/murata-power-s...?ref=lookahead it's only 1.5amp but I think most manufactures of power supplies and tablets build in some cushion. These run very efficient and are cool to the touch SNO

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              • #8
                why buy something you can make?? so a 5v Regulated DC, with more than 2Amp output will be enough? (if i make a 5v 5A, i wont burn anything, correct? :P )

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                • #9
                  Why make something when you can buy it cheaper. better, smaller.... ???!

                  Did you make the PC you are writing your replies on? You can - after all, the original IBM PC used all "off the shelf" components so that anyone could repair it. Mind you, it cost $7,000 in the 1980s. And BTW - do IBM still make PCs?

                  You have noise issue because of your philosophy.
                  Go ahead, make your own dc-dc converter or ancient regulator.

                  You ask if 5A (at 5V) won't burn anything, yet you try to tech me stuff?
                  (Yeah, I think it's time I bug out....)

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                  • #10
                    Originally posted by OldSpark View Post
                    (Yeah, I think it's time I bug out....)
                    yep

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                    • #11
                      the reason i ask about the 5A , is becouse i dont know how the tablets work internally. i dont know if they are designed to drow as much ampere as they can, or if they , limit them. and i am not willing to find it by trial and error. is it so hard to understand it??
                      the reason i try to teach you, is becouse history has proven you need it.
                      the reason i try to make something, instead of buying it, is becouse it's the only way i can be sure, its suited to do what i need it to do.

                      it's true that if i tried to build the first PC, it would cost me, but its also true , that if all people where like you, and always tried to buy something instead of making it, then i would be writing you my reply, from that first IBM pc, ...

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                      • #12
                        Originally posted by settra View Post
                        the reason i try to teach you, is becouse history has proven you need it.
                        When? (LOL!)


                        The basics of electrics - you only need supply the correct voltage; the load takes care of the draw.
                        Does a 10A AC supply blow a 1A radio etc; or a 100A battery supply blow a a 3W/250mA bulb?
                        You don't need to now "how the internals", all you need to know is its voltage and that you can supply or exceed the current required.

                        Sorry for the interrupt, but curiosity got the BETter of me. (I'm betting a 3-way wiki.)

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                        • #13
                          C'mon Settra, what have you tried to teach me?

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                          • #14
                            Originally posted by OldSpark View Post

                            You ask if 5A (at 5V) won't burn anything, yet you try to tech me stuff?
                            you sed it, not me.(unless tech me stuff, meant something else)

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                            • #15
                              I'll put that down to language difficulties.

                              I was asking you to clarify your "history has proven you need it" wrt you trying to teach me stuff. I was hoping for exampless.


                              As to your previous quoting, - if you think a 5V 1,000A supply can burn out a 5A 100mA load, what can I say? Or is an explanation necessary?
                              If I misunderstood your meaning - fine - but I'd still like to know what YOU have tried to teach me.

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