Hi, Can anyone help me I have an old playstation 1 which runs off 7.5V with a jack plug, I want to run it from my car 12V battery, how do I step the voltage down correctly, I have used voltage regulators before for similar projects but I can't find a 7.5 fixed regulator, also how do I calculate the amperage if I were to buy a regulator, thanks in advance chris.:)

You can design a voltage regulator if you have the electronic skills. If not, I'm not sure what to suggest.

The PlayStation 1 probably has specifications about how many amperes it draws. Other than that, you can use an ammeter to measure the current draw when it is in use.

Look through these:
7.5 volt laptop power supply for car - Google Search

It's really imperitive that you know the power requirements. The power supply must be greater than the requirements.

The AC wall wart (the lump that plugs into the wall) should have something on it. Could say 120V @ 0.5A or 7.5 DC at (120*0.5)/7.5 Amps.

Regulated and polarity is next as well as the physical characteristics of the plug. Radio-Shack does sell Adapt-A -Plugs, but the performance [expletive deleted] at 3 amps or so. Tried them for a Laptop. No good. They usually leave out the important information.

A switching regulator is best in this situation.

Just remember that P = Volts * Amps. P can be in VA or Watts. For this application consider them the same.
Power at 120V will be a little higher than at the lower voltage due to heat and efficiency losses. 85-95% is an approximate efficiency number.

Pre-made product will usually be better. Most switching regulators require a PC board, but have few components.
There are plenty of LM317 (Adjustible) type boards from people like Jameco and Jaycar. The 317 is an adjustable regulator for 1.5A with a 3-37V input. Protection needs to be provided for a car environment.

so it's like the LM317 _ hardware and heatsink
2 resistors to set voltage
Probably 3-4 capacitors (Reliability and different types)
diode for -200 V protection
diode for rev polarity protection
diode across regulator in reverse (protection)
Transorb (~18V) - Overvoltage protection

Terminal strip/case/wire/strain relief etc.

You can check out www.national.com and look up the LM317T.

But, we need to know the VA or power, either input or output.

If you have the 120 volt power supply that came with game and it reduces it down to 7.5 volts. Just buy a power inverter 12 volt to 120 AC volt from most auto parts stores or home centers. Get the one with cigarette lighter plug. You can run your Playstation, TV, laptop, cell phone charger, charge up your batteries for your cordless tools, trouble light etc. The more watts you need the price goes up. Divide watts by 120 to give you amps. We bought a 600 watt one for car (5 amps ) it runs a laptop, cell phone charger and games, CD player.
I have a 1200 watt (10 amps) one for work truck . It will handle larger power tools. But you need to place it closer to vehicle battery.
600 watt was around $35 dollars. The 1200 watt was around $200

If you do not have the power supply that come with game, check pawn shops, flea markets , and garage sales.
hawk_eye

Thanks for your answers guys, I really don't want to use an invertor so I need to design something to power it, I origonally wanted to power a playstation 1 @ 7.5 volts, but I have purchased a ps2 now which is a bit better it's the slim ps2 which has a jack plug and separate power supply,. I think it is a regulated supply this time it's 8.5V and says 5.65A, most of the voltage regulators I have seen only go up to about 3A, how would I go about building a little power supply? My electronics skills are not good, but I can solder and I can follow instructions real good. Any suggestions? By the way how many amps would be coming from the car battery at 12V?

Start here:

WEBENCH&reg - Choose a Part

I used 6 A, 8-16 V in, 8.5 V