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USB-PD: Selectable 5v, 9v, 12v, 15v & 20v ‘take anywhere’ DC power supply!

Over the past couple of years I have gained a real interest in USB power solutions, its convenience is second to none and the cheap availability of high capacity 18560 fuelled USB power banks make it a fantastic solution for mobile power. We have all been using USB to charge up phones, tablets and other gadgets for years right?

But what about powering something else? Something that requires more power, such as small laptops, radio’s and other gadgets which exceed the capability offered by the humble 2.1-2.4A @ 5v offered by the humble USB A port.

Lets say you’ve got some devices that accept a standard DC barrel jack and expect 9v, perhaps even 12v? Well there is a half-way house solution for those in the way of a USB 5v to 9/12v step up cable which uses a boost convertor to step up the voltage. However in practice I find these unreliable on anything but the smallest of loads due to the reduced current capability once your low 5v has been boosted to 9 or 12v. I also notice the voltage stability of these step-up cables leaves a lot to be desired and have found a mere 800mA load at 9v to pull the voltage down below 9v, making it unfit for purpose.

Enter USB Power Delivery (or USB-PD for short)

The USB-PD specification is a protocol, delivered via a USB-C interface that enables a supply & a load to negotiate power requirements,. They do this via a series of messages, so data essentially via the USB-C connection immediately after the load is connected to the supply. You could actually think of this as a similar process to how PoE 802.3af or 802.3at is delivered, when a PoE capable device is plugged into a switch capable of 802.3af/at, the switch and device will communicate briefly and request power is enabled.

However, whereas PoE is as standard 48v, ON or OFF, USB-PD has a neat trick up its sleeve.

A USB-PD compliant power supply is capable of natively providing several different voltages ranging from 5v, all the way up to 20v. These are known as profiles, the main ones being 5v, 9v, 12v, 15v and 20v.

This process where a load negotiates power requirements with the supply is known as establishing a power contract and means our load device can receive up to 20v rather than the standard 5v offered by traditional USB.

A USB PD Supply putting out 20v as shown by my inline tester.

You may notice that certain new devices such as the Macbook Pro and other laptops now feature USB-C as their charging connector. This is USB-PD in action already and in the case of the Macbook Pro, it allows for about 90W of power delivery, much higher than the approximateley12w max offered by the humble old standard USB port. A quick look on Amazon will reveal a number of USB-PD capable chargers (aka Power Supplies), the actual specification allowing for up to 100W, but you’ll find 65W capable units being much more common.

USB-PD is a specification that allows for 100W power delivery. However the spec for suitable USB-C cables to carry it only outlines 65W handling. Thus for compatibility, there are more 65W supply’s than there are 100W.

Great! Sounds awesome, but what about powering non USB devices?

This is where things get interesting and we start to see just how much potential there is in USB-PD as an all purpose power source for all manner of DC powered devices.

Since USB-PD is a negotiated protocol, this means there’s data to intercept over that wire and not only that, the protocol is published anyway since that’s how manufacturers implement it into their devices. So what if your load side device wasn’t actually the device you wanted to power? What if it was a simple chipset to present itself as the USB-PD capable load, and then once the power contract has been established, it exposes that power to you via a simple plain old set of screw terminals?

Say hello to the ZY12PDN or ‘USB Poll Trigger/Detector’ as they are called!

This neat little device features USB C on one side and connects to a USB-PD capable supply. This particular model features a click button and a coloured LED that when pressed, negotiates a different voltage with the supply and makes it available to you as a standard screw terminal on the other end. This means, if you have a device that is usually powered by 9, 12, 15 or 20v, then providing your load does not exceed the current rating of the supply, you can connect the appropriate connector (such as a barrel jack, or anything else) and power it from your USB-PD supply!

A ZY12PDN USB-PD ‘Poll Detector/Trigger’.

Always make sure you check the current rating of your USB-PD supply for each of the profiles it supports. For example, a 65W capable supply will usually do 5v 3A, 9v 3A, 12v 3A, 15v 3A and to achieve greater than 45W, using the 20v profile it would supply a max of 3.25A.

So far this is fantastic news for those of us that love gadgets, but die inside when you find something that isn’t powered by USB due to its voltage/current requirements. But it gets better!

We all know about Lithium powered USB power banks for charging up phones etc when on the go or camping. But now they are available with USB-PD outputs as well, meaning you can benefit from this flexible DC power solution, anywhere you are. Simply take a ZY12PDN or similar, a USB C cable, a DC Barrel connector (and series of adapters if you want) with your USB-PD capable lithium power bank such as the 45W capable 99Wh unit shown below and suddenly you’ve broken free from the limitations of USB A 5v power.

You can even fix the output of the ZY12PDN to a selected voltage and essentially turn any DC device within 5-20v into a USB PD powered device.

Combine a ZY12PDN trigger with a USB-C cable and a DC Barrell connector on a tail for the ultimate solution to power non USB devices up to 20v when on the go!
An iMuto 99Wh power bank with 45W USB-PD output.

There are many options available in the way of Lithium power banks with USB-PD outputs. The one pictured above is excellent value, high capacity and offers a 45W capable output. There are others from the likes of RAVPower and Anker with varying capacities and output capabilities so get on Amazon and do your own research.

A useful tool to have for this stuff is the inline USB-C power monitor shown in the above pictures. This is great for getting a voltage readout of the selected PD Profile if you are unsure of what’s going on. This can be found on Amazon here. The best source for the poll trigger / ZY12PDN is either Amazon or Ebay, see an example here.

Anyway I hope this article has enlightened you to just how far you can take USB power solutions, especially when going mobile or out camping etc…

Cheers,
Tom

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