irf9540n switching ext power supply to Pico W

Power Pi Pico by applying 5 V to VSYS—any experiences with or thoughts on additional safety measures?

Ask Question

Asked 7 days ago

Modified 5 days ago

Viewed 68 times


The official Pico datasheet chapter 4.5 suggests using either a Schottky diode or a P-channel MOSFET (P-FET; or a combination of both) when powering the Pico from an external power source (at least if you want to keep the option of simultaneously connecting a computer via USB).

As a suitable P-MOSFET, they suggest Diodes DMG2305UX. However, I couldn’t find this one in online stores here in Germany.

I wondered whether some of you have experiences with one or both of the options and could elaborate what good solutions are and which common diode/MOSFET models are the most suitable for the job (the job being in this case, to power the Pico).

From VSYS and the adjacent GND pin, I power an AirLift FeatherWing to provide the Pico with WLAN, as described in this example. It needs up to 250 mA during Wifi use. Moreover, I want to connect 2 GY-BME280 using i2c and 2 DS18B20 on GPIO 16. These should use something of the magnitude of 1 mA per sensor, which, I guess, is negligible.

The power source will be this 5 V 12 W power supply transforming 230 V 50 Hz AC to 5 V DC.

I attached two images from the original Pi Pico datasheet depicting both versions.

This is their version using the Schottky diode:

Schottky diode version

This is their version using the MOSFET:

MOSFET version

They added: “For inputs that have a low minimum input voltage, or if the P- FET gate is expected to change slowly (e.g. if any capacitance is added to VBUS) a secondary Schottky diode across the P-FET (in the same direction as the body diode) is recommended.”



edited Sep 13 at 20:05

asked Sep 13 at 14:22

Manuel Popp's user avatar

Manuel Popp

16166 bronze badges

Add a comment

Start a bounty

1 Answer

Sorted by:

Reset to default                                              Highest score (default)                                                                   Date modified (newest first)                                                                   Date created (oldest first)                              


Although your question is call for sharing experience, I also have interpreted it as asking for help with realizing the circuits from datasheet. Since you cannot get the MOSFET referenced, you may want simply try alternatives that are on stock in Germany:

  • This one has lower drain current (2.8 instead of 4.2), though with 12W supply it should be good enough. It also has insignificantly (i.e. 50mV) higher gate threshold voltage (450 mV instead of 400mV).
  • This one has 100 mV lower threshold voltage should not matter neither, and lower drain-source breakdown (-12V instead of -20V), since you use it with 5V circuit, you won’t ever exceed 12V, so should be fine too.
  • Finally, this is very close to the original, with very high current rating (13.4 A). It has slightly less standard packaging, which may or may not matter to you.

There are a lot more alternatives at (e.g. Mouser) especially with leg-less SMD packaging.

Note: I only checked catalog values which on rare occasions may not mach to the datasheets. It is a good idea to double-check datasheets before buying and using components



answered Sep 15 at 10:02

Vadim's user avatar


16677 bronze badges

Add a comment

Categories: Uncategorized

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.