If I connect 2 6V batteries or two individual sources serially the combined voltage should be the sum of the voltage of each battery (i.e. 12V). Is it possible to get 12 volts from a single source or battery of 6 volts? Actually I have to power my DSL router of (12v-700mA) from my laptop's USB port (5volts).

Schematic diagram will be highly appreciated.


1 Answer 1


Your laptop's USB port supplies only 500mA. So, that is impossible with the USB port. Because even in the ideal conditions, output power cannot be higher than input power. In your case:

Your output power: 12*0.7= 8.4 Watts

Your input power: 5*0.5(max) = 2.5 Watts

With a 95% efficiency of the converter, you need at least an ~8.9 Watt input power.

However, if you have a higher current source with 5V, you can do it. And the way to convert a voltage by increasing it to a higher voltage is done by a "boost converter"*.

A boost converter is a switch-mode power supply and it can be fairly easy to build one by using a Simple Switcher from National Semiconductor.

Here is a design I selected using WEBENCH. It uses LM2585 at 100KHz. So it will be fairly easy for you to make it work. Because higher the frequency, harder it gets to build it.

*Generally, I think. Correct me here if I'm wrong, guys.

  • \$\begingroup\$ Why the down vote? \$\endgroup\$ Dec 20, 2011 at 9:00
  • \$\begingroup\$ This may not be he, but the Phantom-Coward goes about downvoting some eminently sensible stuff and never explaining why. \$\endgroup\$
    – Russell McMahon
    Dec 20, 2011 at 9:47
  • \$\begingroup\$ lol, actually he/she down voted because I first wrote the first three sentences and then published the answer, immediately after that, I started adding more and published again. in the mean time, he/she down voted. \$\endgroup\$ Dec 20, 2011 at 10:18
  • 1
    \$\begingroup\$ The only objection I can see is your completely pointless and content free first sentence. What exactly is "OK, here is the thing." supposed to convey? However, your technical content is sound and your stupid first sentence doesn't merit a downvote in my opinion. I have upvoted to offset the undeserved downvote. I think I may edit out your first sentence. \$\endgroup\$ Dec 20, 2011 at 13:53
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    \$\begingroup\$ @OlinLathrop I agree that there is no reason for a downvote here, but you should also be aware that downvotes and upvotes are not equal... 1 downvote takes away 2 rep from the post owner while 1 upvote gives 10 rep to the post owner... So for this answer, abdullah has gained 58 rep. Although this answer is good, it is not nearly as good as some answer that get almost no upvotes. Basically what I am trying to say is, we shouldn't be upvoting just to offset one persons down vote. \$\endgroup\$
    – Kellenjb
    Dec 20, 2011 at 14:28

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