The USB Power Delivery (PD) Specification — everything you need to know about USB-PD

USB PD (Power Delivery) is an advanced, fast-charging standard that supports various power requirements over a USB connection. Its predecessor, USB (Universal Serial Bus), was a wondrous invention in the late 1990s and revolutionized how we connected devices to our computers. Before that, we had various serial and parallel connections along with proprietary options.

USB introduced a fixed 5V power supply for peripherals, allowing companies to design around this power requirement. But as time went on, devices traditionally charged via a DC barrel jack moved to USB, and those devices started requiring more power or introducing proprietary protocols. This is where USB PD (Power Delivery) comes in. The first version of USB PD was designed for older USB-A devices; it wasn’t until USB PD 2.0 that USB-C became the dominant interface.

The USB C PD Specification

The key feature of USB-PD is smart power negotiation. The device and the charger communicate with each other and establish the correct power requirements without user intervention.

The specifications for USB-C PD have evolved over the years. We are currently at USB-PD 3.2, which introduced new branding/terminology. The specification defines communication standards that enable the device to report its power capabilities. The latest version of this protocol, the Power Supply Block (PSB), was PSB-P3.1 in 2021, and that standard is backward compatible with previous versions.

As a result of the spec, I can charge my smartphone at 18W and my Lenovo X390 at 65W from the same USB PD charger; there is no longer any need to carry multiple chargers. Even Apple devices, which have long used proprietary connectors, are moving to USB-C due to EU regulatory requirements.

Let's take a look at the specs.

PPS: Programmable Power Supply, introduced in USB PD 3.0 that enables a device to dynamically adjust voltage and current for efficient charging.

AVS: Adjustable Voltage Supply, introduced in USB PD 3.1 alongside EPR. AVS enables a USB-C charger to provide higher voltage and power levels, up to 240W when using the correct cables.

EPR: Extended Power Range, introduced in USB PD 3.1, enables chargers and devices to deliver more than the previous 100W limit. It works with AVS to provide up to 240W.

USB PD 1.0

USB PD 1.0 was the start of the standardization. We only have five power profiles. One for 5V, and two each for 12V and 20V. But each profile is designed for a different device type. At the time, smartphones didn’t use high-speed charging profiles that we have now. Typically, smartphones would charge between 10 and 15W. Headphones, desk accessories, and portable hard drives would run at 10W. You could run higher-powered devices, such as hubs or external GPUs, if you had the correct cable.

There are numerous USB PD 1.0 devices on the market, commonly used to charge smartphones and power USB-A devices that require more power. I have one to power my many USB soldering irons. This version of USB PD may be “dumb” when compared to the newer standards, but it gets the job done.

USB PD 2.0

USB PD 2.0 is where we see USB-C enter the PD standard, and PDO (Power Data Objects) expands the standard to provide additional 9V and 12V options that deliver 1.67 to 3A (up to 27W) for 9V and 1.8 to 3A or 2.25 to 3A for 15V. At 20V, devices can negotiate up to 5A, giving a full 100W of power.

USB PD 2.0 was possibly the most impactful version on the market, largely thanks to the introduction of USB-C to the standard. Most USB-C laptops use this, but it does depend on the manufacturer. The same applies to power banks and hubs. This is the era in which many manufacturers moved away from proprietary power bricks because USB-C offered the power they needed in a very convenient form factor. Notable examples include Nintendo’s Switch, Ultrabooks, and Chromebooks.

USB PD 3.0

USB PD 3.0 brought PPS (Programmable Power Supply) to the standard, with voltages between 3.3 and 21V at 3A. USB PD 3.0 provided a fine-grained approach to power negotiation. By negotiating a more efficient power profile, devices could charge faster and at lower temperatures. There is still the 100W hard limit, but PPS favors efficiency over raw power. USB PD 3.0 is common in flagship smartphones because it supports flexible charging rates, improves battery life, and, of course, reduces heat. These are all factors to consider when charging smaller devices.

USB PD 3.0 is now a decade old and has become the de facto standard for chargers, thanks to its expansive voltage range that supports a wide range of devices.

USB PD 3.1

Released in 2021, USB PD 3.1 introduced Extended Power Range (EPR) that added three new fixed voltages. These were 28V, 36V and 48V. It also saw the max power output extended to 240W when using an EPR cable.

The Adjustable Voltage Supply (AVS) enables 240W by providing 48V at 5. This high power output is typically used with GaN (Gallium Nitride) power supplies that use GaN semiconductors instead of the traditional silicon. The benefit of GaN is that it can be made smaller, more efficient, and it has much better heat dissipation. Other devices that use this standard are high-power laptops, such as gaming and workstation replacements. The Framework Laptop 16 is a chief example of a high-power laptop that employs USB PD 3.1.

USB PD 3.2 had no impact on any of the electrical standards used. Rather, it was a release to align the USB PD terminology with USB-IF branding.

The USB PD standard is constantly evolving, and with USB PD 3.1, we have a connector that offers plenty of power for gaming laptops and even enough power for mini PCs and multi-monitor setups. A future USB PC specification could one day solve all of our power connector problems.