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USB 2.0 Voltage Answered

Can somebody tell me what voltage a USB 2.0 port puts out, what the cable is capable of transferring and how much voltage an Ipod takes in? Thanks, kidboy


The voltage of USB 2.0 is the same as USB 1.1. It supplies 5v at 500mA.

Why did I think it was 3.3 volts?

3.3 volts, or 2.7 volts is what the CPU uses... regulated down from the power supply's 5V bus...

USB ports are supposed to deliver up to 1 amp but typically the desktops will share a 1 or 2 amp power supply among two or more ports...

Worse yet many laptops reduce that output to about 1/4 amp.

SOME phones (and my Motorola Droid are among them) won't charge from 5 volts... their chargers run between 5.5 and 5.7 v

Or I should have said they won't charge from shutdown voltage from a USB port... once they have a partial charge they can use a lower voltage to complete charging....

My Kyocera won't charge on a laptop usb port. It will "maintain" but that's about it. Just not enough amperage at 500 MA. Maybe usb 3 will help us out.

If your "device" needs a voltage more tightly regulated than "4.5 to 5.5V", 3.3V is the closest "standard" voltage to aim for without fancy voltage regulators. There's a good chance the iPod is 3.3V on most of its internal circuitry...

how can we covert 12 volts into 5 volt,,,for usb current only and how to reduce the ampers also, thnx

Can a 6V battery be used to 'charge' devices through the USB cable?

i.e. a sealed lead-acid 6V 4.5 Ahr battery like the ones used in emergency lighting - I am looking for a way to keep a USB camera 'alive' to take a long time-lapse picture sequence. Long in duration taking pictures for a several day period.

Thank you in advance - I am new to this Instructables web page :-) and like what I am seeing posted!

6V is too much. You will need to drop it down to 5V. Placing a protection diode between the battery and the camera should do the trick. Any diode that has a forward voltage of about 1V like the 1N400x series of diodes will be perfect.

Just to add, all voltage from your computer is exactly 5 volts. That is why its important for home-brewed electronics to make sure you have 5 volts, or you will blow out your device you want to charge for example.

5V inside your computer doesn't necessarily equate to 5V at the end of a USB cable plugged into your computer; there can be assorted devices ranging from fuses to electronic switches that can reduce the voltage "some." Also, many laptops work mostly on 3.3V these days, so the 5V may not be as regulated as it was in the old days...

Ohh, right. Thanks for clearing that up.

The specs for a PC PSU are for +/-5%. So the actual output of the 5V rail can be anywhere from 4.75V to 5.25V, if its a good quality PSU. Cheaper PSUs can be as bad as 8% or 10%. But the PC and USB devices will still operate fine at that level. As mentioned the voltage out the end of the USB cable will be slightly lower due to resistance.


11 years ago

USB standard:5V should be 4.5V to 5.5V