DIY Raspberry Pi 4 piCorePlayer Part II - Power Supply

Power Supply

Here comes to the power supply of the RPi, DAC HAT and the touch screen. It is recommended to supply 5V/3A to the RPi 4 and touch screen, together with DAC HAT and some buffer, 5V/5A would be a suitable option for the system. In this project I am using a 40VA R-type audio grade transformer with 8V/5A output capability. 8V is the RMS value without loading. The peak voltage is 8*1.41=11.28V, the low dropout IC requires >1.5V voltage differential, also considering 1.4V drop after the bridge rectifier, 8V output would be a suitable option (provided that decoupling capacitance is large enough).

The power supply circuit is rather simple, LM317 sets the desired voltage, a PNP BJT serves as a switch to provide large current.

Schematic and Layout

Below shows the layout of the power supply circuit. The input and output are placed on the same side in order to shorten the distance between the PCB and RPi 4. The power trace is made as large as possible owing to the large current.

PCB Gerber and Assembly

After the layout is completed, generate the gerber and send it PCB factory for fabrication. Below are the fabricated PCB samples.

After assembly:

The LM317 and PNP transistors are soldered after installation. This is because the case is utlized as the heat sink.

The completed power supply looks like this:

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