Linked Questions

13
votes
5answers
10k views

How does a USB 2.0 Wall Charger negotiate current output?

I'm trying to use a mobile phone charger for my projects, and want a high current output. I have read this, however my measurements show something else. Here is a link to the Battery Charging ...
10
votes
6answers
1k views

USB Power - The basics

I am new to designing something to be powered by USB. Ideally It can either be plugged in to an adapter to a UK wall plug, or a powered USB port on another device. I have the circuit design in place ...
8
votes
3answers
2k views

Best way of making a battery powered USB charger?

I recently made a USB charger that takes a 9V battery. I've noticed it doesn't work with a lot of devices though. It was very simple though, just a 5volt regulator hooked to a USB plug and 9V battery ...
6
votes
2answers
3k views

Critique of my Data logger's Power circuit design

I am laying out my first full device, a fairly simple sensor-data logger, with these specs in mind: I'm running microcontroller and sensor @ 3.3V, with load varying from 10 mA to 400 mA device will ...
5
votes
3answers
19k views

Voltage requirements for charging Nokia phone

I have an old Nokia phone which charges fine from the adaptor, but refuses to charge using a USB charging cable. Note that this isn't a normal USB cable, as you can see from the picture, it's got a ...
4
votes
3answers
1k views

What's needed to get 100 mA from a USB port?

I'm trying to build a stereo speaker system for use on a laptop. I want to keep it as simple as possible, so I'm thinking of using laptop's audio output to for the audio signal and a USB port for ...
3
votes
1answer
214 views

What's the DC voltage range typically tolerated by modern smartphones?

The modern USB charging circuitry of mobile phones is pretty sophisticated. For example they can negotiate higher charging voltages etc. This question, inspired by a discussion on worldbuilding, is ...
3
votes
3answers
1k views

Connecting a higher-current power supply to a lithium-ion charger will damage the battery. Why?

I am not asking how the battery gets damaged, because that answer is straightfoward. What I am asking is why lithium-ion chargers allow batteries to be damaged by excessive charge current in the ...
3
votes
2answers
632 views

Lengthen a AC to microUSB phone charger cord?

Can I effectively take a 3 ft standard cell phone charger (AC to microUSB, 750 mA at 5V) and lengthen the cord to 6 ft by splicing the cord or am I going to lose something in the mix? Do I need to ...
3
votes
2answers
6k views

Make a tea mug heater with a USB power source

For a school project, I have to make a mug heater which draws its power from a computer's USB port, such as this one. I don't mean one that boils the tea, but one that keeps it warm-ish, at at least ...
3
votes
1answer
8k views

How does my phone get charged via laptop USB port at lesser current (compared to wall charger) [duplicate]

Today's typical smartphone chargers are rated at 5 Volt & 1+ Ampere. The laptop USB can supply 500mA 100mA. Why is it safe to charge the phone with 1/2 the rated current? Is it like a slow ...
2
votes
2answers
380 views

connect LEDs to USB keyboard – but they turn off after a second

I have a USB keyboard. As I work many times in the darkness, I put some LEDs into the keyboard case. I connected two pairs of yellow standard LEDs serially to the USB power lines (Vcc and ground, pin ...
2
votes
3answers
2k views

Feeding 2*5V to a 12V fan?

How would I amend a 12V fan to take 2*5V? The 12V fan has 2 wires on it. one would take 12V the other GND. I'd like to be able to feed it 5V and 5V, instead of just 12V. What do I need to do it? ...
2
votes
5answers
8k views

How to adapt a string of 10 LEDs powered by 3 AA batteries to work off a USB port?

I have a string of Christmas lights made up of 10 warm white LEDs. The lights are connected in parallel (not in series). The string works with 3 AA batteries (that is, 4.5 VDC). And all that stands ...
2
votes
1answer
2k views

Risk of overloading a usb charger

I just bought this product: "Jackson PT1USB" as an attemp to get a portable charger for my netbook, ipad 2 and smartphone. Now I am bit worried after reading in the product "total connected load to ...

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