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I'm looking for some help building a circuit to supply a Raspberry Pi Zero, as well as a 1W RGB LED driven through a Picobuck driver. The Picobuck needs 12V and the Pi Zero just needs 5V (from a USB power).

I tried using a 12V to 5V buck converter board, connecting the 12V to the Picobuck and the 5V to the Pi. This is fine until I switch on the LED, which causes the Pi to either reboot or shutdown. I presume there is a voltage drop, or not enough current to keep the Pi running stable?

So right now my project has 2 wall adapters (one USB AC->5V DC, and one AC->12V DC). The project is working well! But I want to eliminate the second power supply.

What do I need / what is a good circuit option to have a single AC power source, and then 2 outputs -> 12V and 5V without a current draw from the 12V causing a ripple or voltage drop on the 5V?

Is there such a circuit design? I can build something if its not too complicated, but I am still a beginner and wouldn't know where to start designing a circuit like this. Preferably I would like to just use my existing AC wall adapter that outputs 12V @ 1A. Is this enough power?

Thanks

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I tried using a 12V to 5V buck converter board, connecting the 12V to the Picobuck and the 5V to the Pi.

That is the basic approach I would take too.

This is fine until I switch on the LED, which causes the Pi to either reboot or shutdown. I presume there is a voltage drop, or not enough current to keep the Pi running stable?

My guess is what is happening is when the picobuck turns on it draws a spike of power that glitches the system power supply.

Unfortunately without an oscilloscope it's difficult to debug this but I would start by adding large capacitors to both the 5V and the 12V rails.

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  • \$\begingroup\$ Thanks. Can you recommend a particular size cap for the 12V and 5V? How many farads is reasonable, and should they be ceramic or electrolytic? Sorry I'm still learning this. \$\endgroup\$ – Jon Mar 6 '17 at 18:29
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    \$\begingroup\$ @Mangist If you have, say, a couple of 47 µF capacitors to hand, try them. (Just be sure the voltage rating of the capacitors is more than the voltage they will have across them.) If not 47, then 10 or 33 or 22 or 100. That sort of range. If that makes it work, you can remove one and see if still works. After testing the idea, you can calculate the minimum required value if you want to. \$\endgroup\$ – Andrew Morton Mar 6 '17 at 18:41

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