Nano power options with NeoPixel strip

Other Hardware General Electronics
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I searched and found only close matches for what I'm wondering. So I am asking here. I have a Nano clone, and a 60 LED WS2812B strip. Today, I found a decent 5V supply so I don't have to rely on the limited USB power any more. At the moment, the strip is just connected to the ICSP header pins, so the power comes from the Nano.

This is where it starts to get interesting. The Nano has a diode between VUSB and 5V to prevent back feeding the USB when external power is applied to the Nano via the 5V pin. That would protect the computer during any combination of PSU or USB power up/down states. But, in the case where the computer is on, and the PSU is turned off, the diode will conduct and attempt to power both the Nano and the strip. That seems ugly to me. I did expect to find some commentary on various sites, for example
https://learn.adafruit.com/adafruit-neopixel-uberguide/powering-neopixels
but that particular use case is not mentioned, that I can see.

In my mind's eye, I visualized the arrangement resulting from removing the diode, which would solve that problem. It would leave the Nano unable to work from USB power, but that is okay with me, as it should be able to run with the PSU parallel connected to both the Nano 5V pin and the strip 5V input.

I have two questions. Why isn't this discussed widely? Will the arrangement (removing the diode) cause any PC USB issue when the PSU (the entire system) is shut down?

My use case: The strip is almost always powered, and it is controlled via the USB serial interface. The computer is usually, but not always on. In rare instances the PSU might be shut down for safety when I'm away. I don't want to plug and unplug any cables whenever I turn things on and off.

Nano Schematic

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Why? There is not only a diode to protect the USB from external power but also a fuse to protect the USB power from being drawn more than 500mA.
If you want to avoid that too, drive the Nano from USB power and drive only the strip from the PSU.
Desolder the diode is an overkill in my opinion.

Probably because most people don't use it that way.

Probably not but you have to check that for your clone because clones often don't have the exact same circuit as the original.

You will get that if you power the strip by the PSU and the Nano by the computer, all without desoldering anything.

3

Add a diode from the 5V power supply to the 5V pin of the Nano.
Then the Nano will always run on 4.5V, and take power from any of the two.
Don't use that 5V pin to power the ledstrip, but power the ledstrip from the power supply and have the grounds connected.
You will not damage your computer. When the diode is short circuit, the strong currents of the power supply can damage the computer, especially when the computer is turned off.

I hope you have that 470Ω in the signal path ?

4

You also mentioned, clone circuits may differ. Notwithstanding that, I have seen some boards get burning hot when the 5V is drawing a lot of current. I want to avoid that.

You will get that if you power the strip by the PSU and the Nano by the computer, all without desoldering anything.

Well, almost. The unit should run stand-alone, no computer or USB attached. Sorry if I didn't make that clear. For that, the strip 5V and Nano 5V must be connected, or else have a diode to draw from the strip, as Koepel mentioned.

It dawned on me finally, that you don't have to connect the two devices power at all, but then it will only operate when the USB is connected. In that case, only 2 wires between Nano and strip, ground and signal.

Add a diode from the 5V power supply to the 5V pin of the Nano.
Then the Nano will always run on 4.5V, and take power from any of the two.

This is better because no mods to the board are needed. However, I ended up lifting one end of the diode off the pad. So I can put it back if need be. Next build I might try it this way, thanks.

I have not installed the large bypass cap or resistor yet, but I will. I wanted to judge the importance by testing without it first. I can report that without the cap, it sometimes resets the MCU. So that is no myth. I assume it is not the missing resistor since the symptom points more to a supply noise issue. I will rebuild the circuit now with both resistor and cap.

As far as "what people are doing", if it is following the Adafruit tutorial wiring, which has separate power for Arduino and strip, it will only operate when both devices are powered. So I guess where I differ is that I demand stand alone operation, no USB power. Everything running from one power supply (doesn't it seem reasonable to want?).

Thanks everyone