In this article, I show you how I designed my own USB-PD (power delivery) programmable power supply (PPS). USB-PD is becoming more and more popular nowadays. I already touched upon the topic when I developed my, first of its kind, USB-PD-compatible breadboard power supply. The power supply can be used to negotiate the typical PD voltage levels between 5-20 V, while the board also provides the typical rail voltages, 3.3 V or 5 V, whichever was selected by the user. This time, I tried to take a bit bigger step: I developed a circuit and firmware based on the CH32X035G8U6 microcontroller. Actually, it is not “just” a circuit and its firmware, but a full product. I added a 2.8” LCD, an INA226 high-resolution power meter, an LM73100 ideal diode, proper banana plugs, and I designed a nice 3D-printable enclosure for the whole thing. So, it is a complete programmable power supply.

The board is based on the CH32X035G8U6 microcontroller. I picked this microcontroller because its development board is easily available from AliExpress, and it supports everything I need. It has native USB and PD PHY, so it can deal with power delivery, and it has all the typical peripherals that one might need: ADC, SPI, UART, I2C, etc. It has a built-in 48 MHz oscillator, so the circuit does not require an external one. Its operating voltage range allows both 3.3 V and 5 V operation. It has 20 KB RAM and 62 KB flash, which is a great leap from the V003 series’ 2 KB RAM and 16 KB flash, but it even out-competes the V006 series’ 8 KB RAM (however, same flash). This specific chip (G8U6) comes in a QFN28 package. It is fairly small, but allows a lot of GPIOs. As usual, I developed the firmware in MounRiver Studio II.

The firmware features the following:

• Full-featured communication with USB-PD power adapters.
• Status reporting through USART
• Power status and power enable/disable via the LM73100 ideal diode
• Displaying status and telemetry on a 2.8” ILI9341 LCD
• Navigating via a rotary encoder
• Measuring output power (current, voltage, power, energy, etc.) using an INA226 chip

The circuit has a lot of principles merged, and initially, I found the project quite intimidating because there were some components or sub-circuits that I had no former experience with. But I trusted the good old RTFM* approach, and it seems that it worked! I spent weeks reading the datasheets of the different chips and understanding their reference designs, and then implementing them into my circuit.

The circuit features the following:

• CH32X035G8U6 microcontroller for USB-PD communication, display control, ideal diode control and power meter control
• MP28167 Buck-boost converter that accepts voltages between 3.3 V and 20 V and outputs a stable 5 V
• TLV76733DRVR low dropout regulator that feeds the whole board’s 3.3 V rail
• LM73100 ideal diode that switches output power ON/OFF and provides a certain level of protection
• INA226 power meter chip that allows a high-resolution output power (current and voltage) measurement
• …and other small circuits and components that allow the whole circuit to operate properly

*RTFM: Read The F***ing Manual.