Need help doing that.

Thread Starter

Lightfire

Joined Oct 5, 2010
690
Hello,

I am planning to make a converter of a DC to DC.:D(I guess, I can't) But it would greatly help me if somebody will post a schematic for it.;)

My input will be so far 12 V DC /as for the AH/maH I don't know (maybe as small current as possible). And the output will be DC 5.0 V@ 350mA.;)

If somebody posted me a schematic for it or circuit diagram for this converter, I would greatly appreciate that. Even though, i can't do but I want to see the schematic, promise I will appreciate that and promise, if I think I can't do, I won't do. I just want to see the schematic for this converter.

Thank ya very much.
Lightfire
 

Wendy

Joined Mar 24, 2008
22,138
That one is actually easy, and safe. A simple voltage regulator will do it, something like a 7805. You will need the same current in as out. You will also need some small capacitors on the input and output.

Another way to create 5V is to use a 6V battery and hang a diode after it, to drop 0.6V and create a 5.4 V power supply.
 

Thread Starter

Lightfire

Joined Oct 5, 2010
690
Okay.

What kind of 7805 do I need to buy to get this kind of outputs, 5.0VDC at 350 maH?

Any help would be greatly appreciated.
 

#12

Joined Nov 30, 2010
18,210
search for LM7805 or LM 7805
Thats all the numbers you need.
You will find many brands that make that chip.
 

mcgyvr

Joined Oct 15, 2009
5,394
and the datasheet will tell you everything you need. Might want to grab a small heatsink too to attach to the 7805
 

Thread Starter

Lightfire

Joined Oct 5, 2010
690
search for LM7805 or LM 7805
Thats all the numbers you need.
You will find many brands that make that chip.
Ok... thanks
Okay. Is this regulator will regulate also the ampere? Or the output ampere will just be the same?
Thanks
 

Wendy

Joined Mar 24, 2008
22,138
It depends on the specific part. There are light weight versions only rated for 0.1A, but most of them are rated for 1.0A. Look for the TO220 case styles.

Note: at .35A they will get hot, very hot.
 

kubeek

Joined Sep 20, 2005
5,719
Ok... thanks
Okay. Is this regulator will regulate also the ampere? Or the output ampere will just be the same?
Thanks
The amperes will be regulated by the fact that the load consumes 350mA at 5V. There is a current limit in those things like Bill said, but that is a limit and not regulation per se.
 

Thread Starter

Lightfire

Joined Oct 5, 2010
690
I don´t really understand your question. You said that the circuit you want to power draws 350mA maximum when powered with 5V. That´s what it does, no resistors needed anywhere.
OK.

Um, ok. now. i need the item lists and schematic.

Oh, pls. pls. pls. im begging. a lot................
 

kubeek

Joined Sep 20, 2005
5,719
You want the output current to be exactly 350mA, or to be no more than 350mA?

Maybe you should post what device you are trying to supply, because this is getting very confused.
 

Wendy

Joined Mar 24, 2008
22,138
OK, this is where Ohm's Law comes in. If you haven't studied it this is the time. It will be forever useful, and always needed.

The load pulls what it needs, dictated by Ohm's Law. A power supply circuit does not provide current, it provides voltage. You wanted 5V with a max of 350ma. If there is no load there is no current. Loads are variable, this is a given. So the lowest resistance this circuit would provide for (using Ohm's Law)

V=IR
R=V/I
I=V/R

R = V/I = 5V/0.35A = 14.28Ω

P = Power = VI = V²/R = V²/I
P = 5V * 0.35A = 1.75W

If the cell phone needs 5V that is ALL that is important. The current number sets itself, according to Ohm's Law.
 

Thread Starter

Lightfire

Joined Oct 5, 2010
690
The charger specs of outputs are. 5.0vdc / 350 mah as said. but the cellphone's batetry specs are 860maH/3.7V/3.2W. EH????
 
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