Linked Questions

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 ...
1
vote
2answers
644 views

How much current will I get from the 5V rail of a Teensy 3.2 powered over USB? [duplicate]

The microcontroller in question is a Teensy 3.2. My understanding is that the most current that you can get from a standard computer USB port is ~180mA; how much of that will current devices attached ...
0
votes
0answers
32 views

Usb charger not charging only with vcc and gnd [duplicate]

I want to charge my tablet on the wall. And I have a charger behind the tablet and connected 2 wires to vcc and gnd, the same pins as usb female, it turns out that I can't have more than 10 mA. If I ...
13
votes
5answers
8k 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 ...
9
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 ...
5
votes
3answers
18k 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 ...
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 ...
0
votes
4answers
4k views

USB PC Current Limit

I want to build a USB device that can draw 1A. Some of the PCs at my office can supply 1A, some only 800mA. The USB 2.0 specification says a device can only draw up to 500mA. I cannot build 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 ...
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 ...
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 ...
2
votes
5answers
6k 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
4answers
4k views

Max current for USB powered Arduino?

My plan is to use a Teensy logic output pin to switch a transistor to switch an infrared LED The LED handles up to 1A peak current. I will use it as a computerized IR remote transmitter so the duty ...
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 ...
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? ...

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