Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Current drawn from an USB port

Status
Not open for further replies.

EngIntoHW

Member
Is it true that 500mA can be drawn from a single USB 2.0 port?
A unit load is defined as 100 mA in USB 2.0, and was raised to 150 mA in USB 3.0. A maximum of 5 unit loads (500 mA) can be drawn from a port in USB 2.0, which was raised to 6 (900 mA) in USB 3.0.
Taken from Wikipedia.

Thanks.
 
Is it true that 500mA can be drawn from a single USB 2.0 port?

Taken from Wikipedia.

Thanks.

This can be a yes and no thing as to a direct answer. I would suggest you **broken link removed** to better understand what current is actually available at 5 volts from a USB port with a focus on USB 2.0. You also may want to read the USB specification. Get familiar with inrush current when connecting things to a USB port.

It is very easy to damage a USB port therefore I suggest you be real careful plugging devices into a USB port. In the case of a desktop system there is plenty of 5 volt power available from inside the case where you don't risk damage to a USB port.

Ron
 
Just to add some more useful info:

An external USB HDD requires about 500mA which can't be supplied through the front end USB connectors connected via ribbon cable to the mainboard.

To provide sufficient power I recommend using a USB-hub containing its own +5V output power supply.

Boncuk
 
the basic rules of USB are;
* The device must use more than 100ma during enumaration
* The device must not use more than 500ma from the USB Portm at any time
* Any device that uses more than 100ma must have its power from a powered USB hub
 
Last edited:
the basic rules of USB are;
* The device must use less than 100ma during enumaration
* The device must not use more than 500ma from the USB Port
* Any device that uses more than 100ma must have its power from a powered USB hub

:confused: Did I say anything deviating from those rules?
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top