[Solved] USB port voltage

[Nakul]

We use the usb port to charge a lot of our devices na... could someone tell me what is the exact output voltage of the usb port..?

[ico]

USB - Wikipedia, the free encyclopedia

[tkin]

@ico, good enough, close this.

[pimpom]

Originally Posted by Nakul

We use the usb port to charge a lot of our devices na... could someone tell me what is the exact output voltage of the usb port..?

While Wikipedia and other reference sources are valuable, in some cases, the sheer amount of information may be overwhelming. Here's a condensed answer to your question:

The short answer is 5V. The two outer pins of the common USB port supplies the +ve and -ve 5V terminals. The two inner pins are the data lines.

A slight expansion: The current that can be drawn from a normal USB port is limited. If a connected device tries to draw too much current, the output voltage automatically drops. This prevents overloading and short-circuits. This is one reason why some USB devices like external hard disks do not function reliably with some computers.

As with many technical standards, there are variations and sub-types.

[tkin]

Originally Posted by pimpom

While Wikipedia and other reference sources are valuable, in some cases, the sheer amount of information may be overwhelming. Here's a condensed answer to your question:

The short answer is 5V. The two outer pins of the common USB port supplies the +ve and -ve 5V terminals. The two inner pins are the data lines.

A slight expansion: The current that can be drawn from a normal USB port is limited. If a connected device tries to draw too much current, the output voltage automatically drops. This prevents overloading and short-circuits. This is one reason why some USB devices like external hard disks do not function reliably with some computers.

As with many technical standards, there are variations and sub-types.

Care to elaborate on that?

[pimpom]

^Not much to elaborate. Some mobo designs limit the USB output current more severely than others. The device can't get enough juice and functions erratically or not at all. To circumvent this, some devices come with two USB connectors but stability is sometimes marginal even then.

I've observed this several times. In some cases, I confirmed the fact by measuring the output voltage at the terminals.

[ico]

Also happens when you cramp too many USB devices to a hub.

[pimpom]

Yep. That happens too.