Point of load DC-DC converter for powering a Raspberry Pi Zero and peripherals.
This circuit provides a DC supply to power a connected load (such as a Raspberry Pi) and attached peripherals. This is useful for applications where one needs to power a Pi (which needs 5 VDC) alongside some other device such as a 12 V relay, but where for practical reasons there should only be one supply (the higher voltage). It is also useful to provide more power to an attached load that would otherwise work at 5 VDC, since the Pi can only provide up to 500 mA to attached loads. The on-board switch mode chip converts the higher voltage down to 5 VDC for the attached Raspberry Pi.
The circuit uses a Texas Instruments LMR33640 synchronous buck converter, capable of accepting a 6-36 VDC input and outputting 1-24 VDC at up to 4 A. The design is based on datasheet recommendations. It also includes a footprint for a Raspberry Pi compatible header so that a Pi can be attached directly, and there is a screw terminal providing the output voltage if this is not used.
The board silkscreen shows the output to be 5 VDC, but it can be changed by substituting different values for R2 and R3. Section 220.127.116.11 states the equation to use and Table 9-3 in the datasheet has some sample values. Note that as of the November 2020 edition of the datasheet, there is an unfortunate typo in Table 9-2 earlier in the datasheet setting R3 10× too low for 3.3 VDC output, giving an output of around 23 VDC instead! I have reported this to Texas Instruments but as of writing it has not yet been fixed.
See the GitHub project for the design files.
I have used this board for various applications, most recently for my watering system.