Consumers know USB from a plethora of devices: it is used to supply power from chargers and power banks to devices, and it can also transport data.
Once you start examining USB more closely, you’ll discover that it has - among many other things - evolved into a highly sophisticated power management system that can be used in many DIY projects. It can often replace cumbersome buck and boost converters, and for certain scenarios, it may even challenge traditional lab bench power supplies.
Overview
The Universal Serial Bus (USB) is an industry standard that defines cables, connectors, and protocols used for
- connection
- communication
- power supply
between computers and electronic devices.
Roots
Introduced in the mid-1990s by a consortium of companies, USB was designed to standardize and simplify the way peripherals such as keyboards, mice, printers, and storage devices connect to computers. The goal was to replace a variety of older, less user-friendly, and incompatible standards:
- Data:
USB today replaces proprietary interfaces like serial and parallel ports. - Power:
USB today replaces proprietary chargers and plugs and provides a solution to charge and power a variety of devices with a range of voltages and currents.
Using as Power Supply
Even though USB was initially focused on data exchange, with the rise of wireless data transmission, USB is now often used primarily as a power supply—for charging smartphones, flashlights, and most other battery-driven devices.
Over the years, USB has transitioned from a simple 5V 2.5W power supply for low-power devices to a digitally-controlled power management system capable of delivering a wide range of voltages from 3.3V to 48V at power levels up to 240 watts.
| USB Version / Spec | Year | Max Power Output | Key Power Features | Typical USB Connectors | Delivered Voltages (Range & Steps) | Negotiation Protocol |
|---|---|---|---|---|---|---|
| USB 1.0 / 1.1 | 1996-1998 | 2.5W (5V, 0.5A) | Low-power devices | USB-A, USB-B, Mini-USB | 5V (fixed) | none |
| USB 2.0 | 2000 | 2.5W (5V, 0.5A) | Same power as 1.1; higher data rate | USB-A, USB-B, Mini-USB, Micro-USB | 5V (fixed) | none |
| USB 3.0 / 3.1 Gen 1 | 2008-2013 | 4.5W (5V, 0.9A) | Slightly higher current for more demanding devices | USB-A, USB-B, Micro-B, USB-C | 5V (fixed) | none |
| USB BC 1.2 (Battery Charging) | 2010 | 7.5W (5V, 1.5A) | Faster charging for phones, tablets | USB-A, USB-B, Micro-USB | 5V (fixed) | Analog (D+/D- shorting & detection) |
| USB PD 1.0 (Power Delivery) | 2012 | 60W (20V, 3A) | Introduces negotiated voltage steps to support high-power devices (like laptops) | typically USB-C | 5V, 9V, 15V, 20V | Digital (USB PD protocol over CC line) |
| QC 3.0 (Quick Charge) | 2015 | Up to 36W (20V, 1.8A) | Introduces adjustable voltage in 200mV steps | USB-A, Micro-USB, USB-C | 5V, 9V, 12V, 20V; 3.6V–20V (200mV steps, often the upper voltage range limited to 12V by chargers) | Digital (D+/D- pulse signaling, INOV) |
| USB PD 3.0 | 2015 | 100W (20V, 5A) | Introduces support for e-marker cables that can actively advertise their capabilities, enabling 100W with appropriate cables | USB-C | 5V, 9V, 15V, 20V (fixed steps) | Digital (USB PD protocol over CC line) |
| USB PD 3.0 PPS (Programmable Power Supply) | 2015 | 100W (20V, 5A) | Introduces programmable current in addition to programmable voltage (current programmable in 50mA steps). | USB-C | 5V, 9V, 15V, 20V; PPS: 3.3–21V (20mV steps) | Digital (USB PD protocol over CC line) |
| USB PD 3.1 (Standard Power Range) | 2021 | 100W (20V, 5A) | Basic member of the PD 3.1 family, remains backwards compatible with PD 3.0 | USB-C | 5V, 9V, 15V, 20V; PPS: 3.3–21V (20mV steps) | Digital (USB PD protocol over CC line) |
| USB PD 3.1 EPR (Extended Power Range) | 2021 | 240W (48V, 5A) | Introduces support for up to 48V/240W for powering high-demand devices | USB-C (EPR-certified cable) | 5V, 9V, 15V, 20V, 28V, 36V, 48V (fixed steps) | Digital (USB PD protocol over CC line) |
| USB PD 3.1 AVS (Adjustable Voltage Supply) | 2021 | 240W (48V, 5A) | Optional feature in EPR that introduces adjustable voltage 15V–48V in 100mV steps. The real upper voltage limit is determined by charger capabilities. Programmable current feature is dropped in this mode (CV only) | USB-C (EPR-certified cable) | 15V–28/36/48V (upper limit depending on charger, 100mV steps) | Digital (USB PD protocol over CC line) |
Note:
Key changes were introduced starting in 2015 when voltages became negotiable with USB Power Delivery, enabling higher currents and support for much more power-demanding devices (like laptops).At the same time, PD 3.0 marked the inflection point where protocol emulation with generic MCUs became impractical due to the introduction of BMC (Biphase Mark Coding signaling), PPS (Programmable Power Supply), and cryptographic requirements. PD 3.1 (2021) and later (e.g., EPR/AVS) further increased complexity with higher voltage/current limits and stricter timing, solidifying the need for dedicated PD controllers (e.g., STM32 UCPD, TI TCPP).
QC3 remains the only widely used specification supporting freely definable voltages (in 200mV increments) that can be easily emulated (triggered) by simple MCUs like Arduino or ESP32. Any specification beyond QC3 requires specialized trigger chips or I2C-enabled helper ICs that handle the complex protocol requirements.
Using for Data Exchange
Data exchange over wires (instead of wireless) is still essential when high performance or speed is required. USB has evolved tremendously over the years, raising the data transfer speed from 12 Mbps in USB 1.0 to 40 Gbps in USB4 (more than 3000x faster).
| USB Version | Year | Max Speed | Key Features |
|---|---|---|---|
| USB 1.0 | 1996 | 1.5 Mbps, 12 Mbps | First standard, plug-and-play, low/full speed |
| USB 1.1 | 1998 | 12 Mbps | Improved reliability and compatibility |
| USB 2.0 | 2000 | 480 Mbps | High speed, bus power, mass adoption |
| USB 3.0 | 2008 | 5 Gbps | SuperSpeed, dual-bus, improved power management |
| USB 3.1 | 2013 | 10 Gbps | SuperSpeed+, reversible Type-C connector |
| USB 3.2 | 2017 | 20 Gbps | Multi-lane operation, Type-C standardization |
| USB4 | 2019 | 40 Gbps | Thunderbolt 3 integration, multi-protocol support |
General Principles
Here are a few general USB concepts you should be familiar with.
Power Delivery
In power delivery scenarios, devices are categorized as source (delivering power, e.g., a power bank or charger) and sink (consuming power, e.g., a smartphone, MCU, or laptop).
In modern USB versions, source and sink actively negotiate the optimal voltage and current. USB cables with e-markers (specialized chips) contribute to the negotiation: only when the cable indicates it can handle high currents will the source actually deliver them. Unmarked cables trigger low-power modes (and can slow down charging).
A special challenge are devices that can act both as source and sink, such as a power bank (and sometimes even a laptop): they can supply power, but they can also be charged (consume power).
When such devices are connected, part of the negotiation is to determine which device takes on the role of source and which acts as sink. If this negotiation fails, malfunction or even damage can occur.
Data Transmission
For data transmission, USB is a host-centric, asymmetric architecture. The host (typically a computer) manages communication, while peripheral devices (such as flash drives or cameras) connect through USB ports.
Devices can be connected in a star topology, often using hubs to expand the number of available ports. The interface supports “hot swapping,” allowing devices to be plugged or unplugged while the system is powered on, and “plug and play,” so most devices work automatically without manual configuration.
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(content created Jun 25, 2025)