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Building a small 5V 2A Power source

Stotle86

Mar 24, 2011
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I am trying to build a power source for an HDMI splitter. Its requirements are 5v DC @ 2A and I was hoping to use a 9V battery for power with and LM7805 voltage regulator. I'm not sure what else I would need. I am trying to keep it as small and portable as possible. Is there anyone that may be able to help me with wiring or design ideas?

Thanks,
Josh
 

davenn

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Sep 5, 2009
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Hi Josh, welcome to the forums

well a 7805 wont do 2 Amps for a start its rated for around 750 mA, 1 amp at extreme if very well heatsunk.
what sort of 9V battery ? if its one of those small ones a 9V, PP3 type, like this
http://en.wikipedia.org/wiki/Nine-volt_battery
its not going to last long drawing 2 amps, maybe a few minutes.
your hdmi splitter is going to be in near contineous use, or at least for several hours at a time.
a suitable plugpack would be the way to go. :) Portability isnt really an option
Does it really draw 2 amps ?

cheers
Dave
 

Stotle86

Mar 24, 2011
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I'm not sure if it actually draws two amps. The AC adapter touts a 2A output but that seems pretty high. I'm using this for a split off of a DSLR so the power has to be portable and last several hours. That's why I had hoped to use the 9V PP3 type as it is small and inexpensive to replace. Unfortunately my electronics knowledge is pretty limited so I'm not really even sure where to start.
 

davenn

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I'm not sure if it actually draws two amps. The AC adapter touts a 2A output but that seems pretty high. I'm using this for a split off of a DSLR so the power has to be portable and last several hours. That's why I had hoped to use the 9V PP3 type as it is small and inexpensive to replace. Unfortunately my electronics knowledge is pretty limited so I'm not really even sure where to start.


yup ok,
I found so data on the 9V battery, it only has a 600mA/hr rating thats 600mA (0.6A ) for 1 hour and its dead and thats not for contineous drain its only ~ 500mA at contineous.
and thats for a good quality Energiser Alkaline one.

so any battery would have to be something more substantial ... say a 12V, 7.2 A/hr,
sealed lead-acid would give you plently of reserve for a 2 hr or so session.
They may make a slightly lower 12V amp/hr rated one .. Im not aware of... say 4 or 5A/hr

a 12V 7.2 A/hr one isnt light ~ 1 to 2 kg but you would be portable :)

Dave
 

Stotle86

Mar 24, 2011
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Thanks for the advice. :) I was able to dig up a 12v 7A/h battery. Cyclic use has a 2A max. This should work according to your last post. Now my issue is regulating the voltage to work at 5V. If the 7805 won't handle the current are resistors the answer? Or do I just need a beefier voltage regulator?

Thanks,
Josh
 

davenn

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You just need a better voltage regulator. there are some nice buck converter regulator IC's out there that are very efficient, like the LT1070 the datasheet has a good 5V and up to 4 amp reg cct.

Or you could use a LM338 3 pin adjustable regulator, smaller component count but not as efficient (ie. more regulator heat generated). I have usd a number of them over the years, they work well.

Dave
 

Stotle86

Mar 24, 2011
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Brilliant! Now I have some shopping to do. Thanks for all of your help brother, its greatly appreciated! :D

Josh
 
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