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Hard Drive Power

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AtomSoft

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Hello all, as we all know a internal PC IDE harddrive uses 12v and 5v Power at about a max of 1A ... My Harddrive states

12v- 0.90A
5v- 0.65A

I was wondering... i have a Laptop Power Brick.. Universal which can supply 15-24v @ 5A

Can i set it to 15v and use a 12v and 5v (LM7805,LM7812) regulators to supply power without anything blowing up?
 
Should work just fine.
I have a number of older external hard drives that use a single 12 volt input but then have an internal regulator inside for the 5 volt power source.
 
ah... so you think its better to supply the 5v from the 12v regulator? or leave it as both source from the 15v?

Ill use a old PC power supply for now but would like it to look neat so plan to use the Laptop supply
 
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That part is up to you really.

I was just stating that my factory made units only used one regulator being they already had the 12 volt power source available.
 
ah... ok thanks. I was thinking since this puppy can supply 15v @ 5A maybe i can get away with using a 2A or 3A 12v Regulator and powering the 5v Regulator from it... Like:

power-jpg.50903
 

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The 12 volt regulator will have to dissipate a little more but the 5 volt will dissipate less so the average will be more balanced out between them for individual losses.
It would be my choice plus if the 15 volt source ever got replaced with a 12 volt one the first regulator could then be eliminated all together.
 
Ah yeah thanks! This will be my plan then... at least i have the schematic ready for a small PCB heh... just need to make a nice 4 PIN for wires heh... and a Barrel Jack and perhaps a Bridge Rectifier ...
 
Here is a PC and Schematic for all those who want it:

Also NOTE***

C1 = 10uf
C2 = 10uf
C3 = 1uf
C4 = 1uf

or what ever you think is best heh
 

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Hi Ya Jason

The laptop brick puts out AC? I would have guessed DC but I see you added the full wave bridge to your circuit. Just curious.

Ron
 
Got it and thanks for explaining it. I was just curious as to the why. Have a good one...

Ron
 
Heh i did it and it works fine! but gets hot easy and fast. I have 2 heat sinks on them i hope it works for a while until i buy this:

**broken link removed**
 
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I altered the schematic and will make a new board. Perhaps its heating up because im powering it from the 12v LM7812 ? So its drawing to much from 1 regulator. Here is the new schematic
 

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Given that both are linear regulators the total power dissipation will still be the same regardless of if they are in series or parallel with each other.
if you are supplying .9 amps at 12 volts from a 15 volt source you get (15 - 12) * .9 = 2.7 watts. And (15 - 5) * .65 = 6.5 watts.
So the total dissipation that way is 2.7 + 6.5 = 9.2 watts.

If they are series you get (15 - 12) * (.9 + .65) = 4.65 watts. And (12 - 5) * .65 = 4.55 watts which means that 4.65 + 4.55 = 9.2 watts again.

I suspect your heat sinks may simply not be large enough for the peak losses involved.
 
You also have to remember. If i draw 0.9A from the 12v there is only 0.1A MAX left for the 5v regulator which is trying to draw 0.65A ...

Think of it like this... im drawing 1.55A from a 1A source... instead of drawing 2 separate AMPS from a 5A source...

You get it?

IN = 15v @ 5A
OUTA = 12v 1A
OUTB = 5v 1A

Its hard to supply 1 A for 12v and 5v if im taking power from the 12v to supply to the 5v. Now if i take from the input there is enough to share.
 
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Yes I am aware of that but I went by your post 5 where you mentioned using 2 or 3 amp regulator for the 12 volt circuit.

ah... ok thanks. I was thinking since this puppy can supply 15v @ 5A maybe i can get away with using a 2A or 3A 12v Regulator and powering the 5v Regulator from it...

Now if that changed I was not aware of it so then yes they both would need to be independent.
 
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