The correct answer is that a standard USB port outputs 5V.
As stated in the reference, "The USB port outputs 5V." This is the standard voltage level provided by most USB ports (like those on computers, laptops, wall adapters, and power banks) for powering connected devices and charging batteries.
Understanding USB Voltage
When you plug a device into a USB port, the power pin on the USB connector provides a nominal voltage of 5 volts. This 5V supply is a universal standard defined by the USB specifications (like USB 1.x, 2.0, and 3.x), ensuring compatibility across a wide range of peripherals and host devices.
Why You Might See 3.3V
While USB provides 5V, you might encounter 3.3V in electronics projects or within devices powered by USB. This lower voltage is often used by low-power digital logic circuits, microcontrollers (MC boards), and sensors.
Here's how 3.3V relates to the 5V from USB:
- Voltage Regulation: Devices that require 3.3V typically take the incoming 5V from the USB port and pass it through a component called a voltage regulator.
- Stepping Down the Voltage: As explained in the reference, "If you want to power peripherals from the 3.3V pin of an MC board, the current passes through a voltage regulator, reducing the incoming 5V to 3.3V...". This regulator lowers the 5V down to the required 3.3V.
- Current Limitations: It's important to note that this regulation process can sometimes limit the total amount of current available at the lower voltage, "and also decreasing the amount of current you can use to power your peripherals."
So, think of 5V as the power source from the USB port, and 3.3V as a voltage level derived from that 5V by the connected device's internal circuitry.
USB Power Levels at a Glance
A simple comparison:
| Voltage Level | Source | Typical Use Cases |
|---|---|---|
| 5V | USB Port | Powering devices, charging, source for regulators |
| 3.3V | Voltage Regulator (fed by 5V) | Microcontrollers, sensors, low-power digital ICs |
In summary, the USB port itself provides 5V. Any device needing 3.3V from USB power does so by regulating the standard 5V down to 3.3V internally.
