PS/2 Port

[LunarMist]

Does anyone use a notebook PS/2 port as a 5V power supply for other devices? PS/2 devices seem to be spec'd at 100 mA, but the port clearly supplies more than that. For example, there are PS/2 taps for 2.5" USB/Firewire drives. What is the maximum allowable current drain? Is there a standard for current limiting, such as linear or foldback?

 

[Tea]

Juzt take it up till it starts smoking and the lights go out, then back it off a half a turn.

 

[time]

A common opinion is 500mA, or "a few hundred milliamps".

For example.

There's also a vague possibility that the mouse port won't have the same capacity as the keyboard port. I have no idea how you can check this.

The keyboard port doesn't have fancy current limiting - it has a fuse. Which incidentally is typically 1A. Supposedly ...

 

[Tea]

Fuse. Eeek! That makes my let-the-smoke-out theory sound pretty likely. How many people are going to be able to replace a motherboard fuse?

 

[Mercutio]

They don't. I have a bunch (well, four) of Epox boards with bad fuses on the PS/2 ports. I still use them, but it was annoying to have to replace a keyboard I like with some USB POS.

 

[LunarMist]

There's also a vague possibility that the mouse port won't have the same capacity as the keyboard port. I have no idea how you can check this.

There is only one PS/2 port for use either with an external mouse or keyboard. I was hoping for linear current limiting or at least an SMD Polyfuse. I mean, they are so inexpensive.

 

[time]

Whoops, I forgot you said notebook.

Unless the manufacturer used it to power accessories, I wouldn't even count on the 500mA - laptops seem to have less margin in every other respect when compared to desktops, particularly anything that draws power.

But I'm afraid that's just a guess.

 

[Explorer]

A common opinion is 500mA, or "a few hundred milliamps".

There's also a vague possibility that the mouse port won't have the same capacity as the keyboard port. I have no idea how you can check this.

The keyboard port doesn't have fancy current limiting - it has a fuse. Which incidentally is typically 1A. Supposedly ...

One whole amp? Jeez... I'd be surprised if it's more than 500 mA.

By the way, keyboards aren't the only "popular" device that plugs into the keyboard port (PS/2, AT), barcode readers -- and there are many many millions of them out there, just not likely on my (or your) PC -- firmly take up the second most popular spot of things that plug into the keyboard port. Yes, there are some that plug into serial ports, but those are mostly barcode scanners from the past, as the ones that plug into the keyboard port are vastly more popular because they are much easier to integrate.

Of course, the new generation of USB and wireless barcode scanners are making their way onto newly commissioned systems.

 

[Howell]

I Read your posts time. 8)