5V 500mA DC to 1V 500mA DC

[binarycow]

Hello, this is my first post

I've come across a very interesting situation, and I think I've found the answer. Short story: I have 5V 500mA DC, and I need 1V 500mA DC.

Long story: I have a KVM Switch, with no power cord. I also have a shortage of outlets in that area. Installing more, or getting a power strip is not an option (I'm in Iraq, limited funding/supplies - and not as much fun!).
My first thought would be to buy a power adapter. I can't find one that provides this voltage/current. My second thought was to build an AC to DC converter, and step down the voltage appropriately.
Then I stumbled across some interesting articles, and it turns out USB provides 5V 500mA DC. There's gonna be 3 computers next to the KVM switch, all with an open USB port.

Bingo. Thats what I wanna do. I researched it, and I came up with a Zener Diode. I've come across a couple schematics too, but not being an electrical person, I dont quite understand.

So, if you could please, I was wondering if you could please explain to me how the hell people know what size resistor, the voltage of the Zener diode to use, etc. I dont want you to tell me the answer, I wan't to know why

Also, with that, any alternate recommendations other than a Zener Diode?

 

[audioguru]

Nobody makes a zener diode with a voltage as low as only 1V.
Resistor values are simply calculated by using Ohm's Law. Look it up in Google.

An LM317 adjustable voltage regulator IC has a minimum output voltage of 1.25V. Since you want only 1.0V then you must make your own voltage regulator that isn't easy for a noobie.

I would use an LM10 which is an opamp with an adjustable voltage reference and a power transistor to make a 1.0V at 0.5A voltage regulator.

 

[mneary]

1) Supplying 1V to a logic device is quite unusual. Do you know what's in it?

2) I haven't seen a lot of KVMs, but all that I have seen were powered by the computer (5V from the PS/2 connectors).

 

[justDIY]

1v power for a kvm, no way, that doesn't make sense. most of the logic chips out there are 1.8v at best, most 2.0 or 2.7v, and the rest are 3.3-5v. how did you arrive at the 1.0v requirement?

 

[binarycow]

The KVM switch has written next to its power socket thingy (dont know the technical name for it) 1V 500mA.

I havent been able to test it without supplying external power, as I don't have PS2 ports on my computers (The appropriate adapters are on order)

Audioguru: Thanks for the advice, I will look into it today while im at work.

 

[binarycow]

Well, I got my PS2 to USB adapters today, and apparantly it doesn't require external power. It pulls it from the PS/2 ports. Thanks for that suggestion mneary, I never even would have tried it lol.

Thanks for your help guys, much appreciated

I am still curious how I would pull this off, if it were a different voltage. Perhaps you guys would be kind enough to maybe help me to understand how a 12V to 9V adapter would work? Not just a schematic, but WHY things are set up the way they are, so I could, in theory, do it later, on my own

Thanks alot