I am a bit of a nerd when it comes to portable / off-grid power solutions for my devices, namely laptops, phones, tablets etc… I have several off the shelf ‘USB power banks’ from the usual brands like iMuto, Ravpower and Anker, with capacities ranging from 5000mah/18wh to 27000mah/99wh. Traditionally these battery packs consist of a bunch of 18650 lithium cells @ 3.7v connected in parallel to achieve the desired capacity, then coupled to a low cost 5v boost/buck convertor with a couple of USB A ports which can put out 2.1A each @ the USB standard of 5v. This is functional for small devices such as phones, however with only a max 10w output it is dated and somewhat slow. Batteries in phones are getting bigger and bigger, plus support for higher wattage charging is becoming the norm… We are rapidly exceeding the usefulness of the humble USB A 2.1a @ 5v output.

A 99wh pack with 45w USB PD by iMuto.

Enter quick charging standards that seek to expand on the convenience of USB by increase the max power it can provide. There are a number of protocols/standards, some of which are manufacturer specific, some which are widely adopted but still proprietary, and one which is a universal and published standard. These are Qualcomm’s QC2.0 /QC3.0 which provide 9 or 12v over a standard USB A port, up to around a max of 18w, the requirement being a Qualcomm chipset in the device. You also have some very closed shop systems such as Huawei’s 40w ‘Super Charger’, and ‘Dash Charge’ by One Plus.

These solutions all have their place, but they are all half-way houses… There is one defined standard, openly published and maintained by the USB Implementers Forum that promises much more than all of the above… Enter USB Power Delivery, or USB PD for short.

Why is USB PD so good?

USB PD totally changes the game when it comes to the capability of delivering power over USB. Firstly it utilises the USB C connector, which is awesome in every way, and secondly it is capable of delivering up to 100 Watts of power which is enough to charge the current Macbook Pro and many other powerhouse laptops/devices at full speed, no compromises. It is a dynamic protocol whereby a power contract is negotiated between the supply and load.

This power contract may be met at a selection of different voltages, the standard voltage profiles available to USB PD are 5v, 9v, 12v, 15v and 20v. If you have a 100w capable USB PD supply then it can meet this load by supplying 5A at 20V. There are 3 amp current limits for all voltages below 20v meaning a maximum of 45 watts may be delivered by using 15v (15×3) until 20v must be used between 45-100w. For devices that have a USB-C connector but do not implement the USB PD standard, the default profile is 5v 3A meaning your supply won’t all of a sudden ram 20v into a device that’s only expecting 5v.

Wait, can I power non USB-PD devices within this 100w limit as well?

Yes you can! And this is where the fun starts since now that we have 100w (supply dependant) to play with, wouldn’t it be great if we could fake/spoof the load and select which voltage profile we want from the supply? Well, we can thanks to a nifty little device called a USB PD ‘Poll Trigger’ or ‘Detector’. These devices connect to your USB PD supply, and let you select a specific voltage via click button, at which point its available on the other end of the device via some standard screw terminals or solder pads. Attach a standard barrel connector to this and there you have a way to leverage USB PD as a multi voltage power supply upto 20v 5A. With the right adapter, this allows you to power a variety of Lenovo Thinkpads from a USB PD supply as well!

USB PD Poll Trigger/Detector

So to wrap this quick insight into USB PD up, if like me you have been using 5v USB power for a number of years but have found yourself stuck when it comes to fast charging, and devices with higher power requirements…. Then consider yourself enlightened. A native, multi-voltage power supply up to 5 amps at 20v, in the convenience of a USB C connector, able to power beastly laptops, tablets, and various other devices that arent even USB PD themselves!

Cheers, I will be following this up with other articles on my adventures with mobile power.


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