What is Qualcomm Quick Charging (QC)?

It’s confusing. A lot of people think Qualcomm Quick Charging (QC) is the same as the Wireless Power Consortium’s Qi standard. After all, how many things start with Q anyway, and both of them have to so with cell phones. So, you can be forgiven for thinking they’re the same thing. Let’s talk about why they aren’t.

It’s the wire.

Qi is a wireless charging standard. It’s designed to let you put your phone down, without even having to plug it in, and then it just charges for you. However, because of the way that wireless charging works, it’s never going to be the fastest way to charge your phone. You lose a certain amount of energy when you broadcast wirelessly, that’s always going to be true.

Qualcomm’s Quick Charging (QC) standard isn’t about convenience, it’s about speed. If you are willing to hook that phone up to a wire, it’s about giving you the fastest charge there is. And it does so as smartly as possible, and (for the most part) as safely as possible.

Watt’s the buzz, tell me watt’s happening.

A watt is a useful measure of the power that’s actually getting to a device. I could get really detailed, but for the most part just think that more watts=faster charging.

The original USB standard always let you power things, but the amount of power isn’t very big. If you connect up to a standard USB 1.1 port, you’ll get a maximum of 2.5 watts which is enough to power a keyboard or a very efficient hard drive but it’s a paltry amount of power really. Connect the “cube” charger supplied with most phones and you’ll get 7 watts. Obviously better but we want more. Connect the fast charger that comes with an iPad or top-end Samsung device and you’ll get 12-15 watts. Now we’re talking.

Qualcomm’s Quick Charging aims to get even further. Some devices can use up to 45 watts of power to charge and if you do the math that will tell you that potentially, your phone is charging about 6 times faster.

Just one thing…

You have to be careful when you put a lot of power into a confined space like a battery. It’s never a perfect transfer and two things will always happen. As the battery receives power, it’s going to swell up somewhat as the energy makes the battery’s atoms move around. Also, the faster you put that energy in, the more heat is going to be generated as a waste product. If you put too much power into a battery too fast, as Samsung found out with its Galaxy Note 7, it all goes boom.

That’s where QC comes in.

QC is built into Qualcomm’s phone CPUs and it intelligently monitors everything to make sure that as much power gets to the phone as possible and still doesn’t cause it to turn into a little hand grenade. Because a lot of Android phones use Qualcomm’s Snapdragon CPUs, they get the QC technology at the same time.

QC is available right now in two versions: QC 2.0 and QC 3.0. QC 2.0 is the most common and it’s what you’ll find in Samsung’s latest phone. This standard allows for three different voltages to be used, (5, 9 and 12) and that means three different speeds of fast charging. QC 2.0 phones can also charge at regular speed and “slow” (USB 1.1) speed so that’s five different options that the QC processor can use to provide the most power safely. If you have a QC 2.0 phone you might notice that it says “fast charging, slow charging,” or just “charging” depending on where it’s plugged in. That information lets you know whether or not the charger and cable are capable of providing enough power for QC 2.0 to use all its tricks.

QC 3.0 is even fancier, because it allows for variable voltage from 3.2 – 20 volts, meaning that the phone is always going to charge at the fastest possible speed. It’s only available on a handful of phones right now including some LG phones but it’s coming.

And, of course, there is a QC 4.0 standard out there but nothing uses it yet.

You need the right charger.

In order to supply enough power for quick charging, you need a power adapter that supplies the right number of volts, amps, and watts. You can see the rated voltage and amperage in tiny letters on the charger. If you want to quick charge, you’ll need at least 5 volts and 2.4 amps, and if you want the fastest for QC 3.0, you’ll need 20 volts and 3 amps. If you want to know the wattage, multiply volts by amps. If only the wattage is listed, assume that it’s only 5 volts and probably won’t work for wireless charging.

It would be best if your charger were QC certified but since all the hard work is done inside the phone most chargers will work as long as they supply the right amount of power.

While it’s possible to do QC 3.0 with an old MicroUSB connection, the MicroUSB standard doesn’t really support quick charging so that’s why you’re finding phones going to USB-C (that, and USB C is easier to connect.)

Will Apple adopt QC?

Actually they already have. If you have the latest iPad Pro 10.5, it supports QC 2.0 over a lightning cable with a USB-C connector on the other end. Apple does sell a lightning-equipped charger but of course it’s insanely expensive. Luckily all current Apple products will at least use Apple’s non-standard 12 watt power adapter to charge about 50% faster than the little cube you get with an iPhone.


About the Author

Stuart Sweet
Stuart Sweet is the editor-in-chief of The Solid Signal Blog and a "master plumber" at Signal Group, LLC. He is the author of over 8,000 articles and longform tutorials including many posted here. Reach him by clicking on "Contact the Editor" at the bottom of this page.