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Introduction to USB Power Delivery
2026-09-09 | By Maker.io Staff
Before USB became the de facto charging standard for mobile devices, manufacturers used proprietary chargers and connectors that were incompatible with one another. Mini-USB and Micro-USB improved interoperability, but chargers were frequently optimized for specific devices and often performed less efficiently with others. USB Power Delivery (USB PD) was introduced to address this, along with the growing demand for faster charging and for larger, more capable devices.
Device Chargers Before USB
Before USB became a widely used standard in the early 2000s, most mobile devices used custom, manufacturer-specific power supply connectors and data transfer cables. This meant that customers received a new charger for almost every device they purchased, and most chargers were incompatible with other devices, sometimes even those made by the same manufacturer.
Even after the introduction of Mini-USB and later Micro-USB, charging was still relatively limited. Early USB chargers typically operated at a fixed five-volt output and only supported limited charging currents, often only a few hundred milliamperes. In most cases, devices could not dynamically request different voltage or current levels depending on their power requirements. These limitations significantly restricted charging speeds and made standard USB unsuitable for larger or more power-hungry devices. However, some manufacturers used custom protocols to exceed these limitations.
USB Power Delivery (USB PD) was first introduced in 2012 to address these restrictions. It is a separate charging standard that enables compatible devices and power supplies to negotiate power delivery dynamically.
Before USB, most devices required proprietary chargers.
How USB PD Improves Charging Efficiency
USB PD was introduced in 2012, separately from the core USB standard and USB-C specification. However, it became closely associated with USB 3.1, which was released shortly after in 2013, and with USB-C, both of which provided the foundation for faster communication, higher charging power, and more advanced USB features.
USB PD defines that the charger and device can dynamically negotiate charging voltage and current instead of relying on a fixed power output. This approach helps make charging faster and more efficient, since devices can safely request more power when needed. Additionally, devices can instruct the power supply to reduce power delivery based on factors such as battery charge level or temperature, which helps reduce unnecessary thermal and conversion losses.
By supporting multiple voltage and current profiles, USB PD also improves compatibility between devices made by different manufacturers. Customers can use a single charger to power different devices, which has become increasingly important after USB-C became the primary charging standard in the EU for many portable electronic devices with different power requirements.
To use USB PD features, such as higher voltages, faster charging, and dynamic power negotiation, both devices and the cable must support the standard. However, USB PD remains backwards compatible with older hardware to some degree. For example, a USB PD charger can usually still charge devices that do not support USB PD, while USB PD-capable devices can usually still charge from older USB power supplies.
It’s worth noting that, although USB PD and USB-C are strongly associated, a USB-C connector alone does not guarantee USB PD support. USB PD comes at the cost of additional complexity, as devices and chargers require more advanced charging circuitry.
USB PD Evolution Over the Years
The first version of USB PD introduced general power negotiation features and different fixed power profiles that devices could choose from. Using USB PD, devices could request up to 100 W in some configurations, a massive increase from the 7.5 W previously allowed by the USB Battery Charging specification.
USB PD 2.0 was released as part of the USB 3.1 suite of specifications in 2014, and it laid the foundation for the widespread adoption of USB-C fast charging. While the first version relied on a small number of fixed power profiles, USB PD 2.0 replaced this approach with more flexible power negotiation rules. These rules let devices and power supplies agree on voltage and current levels more dynamically while still keeping a small number of standardized voltage levels, namely 5 V, 9 V, 15 V, and 20 V.
USB PD 3.0, added an optional Programmable Power Supply (PPS) feature allowing more fine-grained control over voltage and current levels. Devices can request a voltage between 3.3 and 21 V in 20 mV steps and current levels in 50 mA steps instead of relying on predefined profiles.
USB PD 3.1 extended the voltage range and introduced Extended Power Range (EPR) mode, which adds higher voltages of 28 V, 36 V, and 48 V and can provide up to 240 W. This update also introduced Adjustable Voltage Supply (AVS) functionality, allowing compatible devices to request voltages between 15 V and 48 V in 100 mV steps. Earlier USB PD power modes were renamed to Standard Power Range (SPR). USB PD 3.2 is the most recent revision, and it was released in 2023. This revision enables AVS for the older SPR mode down to 9 V.
USB PD Programmable Power Supply
Earlier USB PD versions relied mainly on fixed voltage profiles that devices negotiated beforehand in a full negotiation cycle. The power supply then held that profile until the device requested a different one through another negotiation cycle.
In USB-C systems, USB PD power negotiation takes place separately from the USB data lines on a dedicated configuration channel (CC). Before delivering higher power levels, the charger operates at a safe default of 5 V. The device and the charger then exchange information about supported voltage and current levels: the charger advertises its available profiles, after which the device selects an appropriate one, and the charger switches to the requested output, completing one negotiation cycle. If the device later requires a different voltage or current level, another full negotiation cycle usually takes place.
The optional Programmable Power Supply (PPS) feature, introduced with USB PD 3.0, improves this behavior. It allows devices to request smaller voltage and current adjustments continuously during charging rather than switching between a small number of fixed profiles. The adjustments are finer (typically in 20 mV and 50 mA steps), can happen more frequently, and they do not require full negotiation cycles. These changes put a greater focus on charging efficiency and power delivery optimization, thereby reducing heat generation and power conversion losses.
However, for USB PD and PPS to function correctly, both the charger and the device must support the standard, and the cable must be rated for the requested power levels. The device also remains responsible for managing the actual charging current and charging pattern, typically through internal charging or power management circuitry. The device can request appropriate power levels based on various factors, such as battery type, charge level, temperature, and general power requirements.
Summary
USB Power Delivery (USB PD) is a charging standard introduced to overcome the limitations of earlier USB charging systems, which typically relied on fixed 5 V outputs and limited charging currents. By allowing devices and chargers to negotiate voltage and current levels dynamically, USB PD supports faster charging, far higher power delivery, and improved efficiency.
Over the years, the specification evolved from using a small number of fixed power profiles to including more advanced features such as Programmable Power Supply (PPS) and Extended Power Range (EPR). These additions allow compatible devices to request more fine-grained voltage and current adjustments, which helps reduce heat generation and power conversion losses while simultaneously supporting higher power levels.
Although USB PD is closely associated with USB-C, a USB-C connector alone does not guarantee USB PD support. To use advanced USB PD features, all involved devices and the cable must be compatible and support the requested power levels.
