Power directly via 3.3 pin

After seeing several threads (like this one) I made a setup that powers a Photon directly via the 3V3 pin. I use a switch mode converter (Murata oki-78sr) to produce a clean 3.3V from the 12V input.

For some reason, the Photon got really hot, behaved erratically and then died. I measured all pins with a multimeter. Only 3V3, VIN, and the I2C lines read 3.3 volts. All other pins measure 0V. To me this looked perfectly fine, so I put in a new Photon and … it died too after a few seconds of operation.

The first time I had USB plugged in also, but the second time the USB wasn’t connected. I need this solved before plugging in another Photon, but I’m out of ideas as to why this happens. Could it be that there are issues with powering with 3.3V directly? Anyone?

It could be that the power supply you’re using is very noisy, which can wreak havoc on your device. Placing some filtering caps on it might help alleviate that.

What’s the 12v input source? A battery?

I’m using an adjustable wallwart, so that might certainly be relevant. I’ll pick up some new Photon’s tomorrow and try that. A 10uF electrolytic and a 0.1uf ceramic should be sufficient? I’ll pick up a different Power supply also.

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You definitely cannot power by 3V3 and any other method (USB or VIN) at the same time. There is no diode like with VIN, and the data sheet does say:

This pin is the output of the on-board regulator and is internally connected to the VDD of the Wi-Fi module. When powering the Photon via VIN or the USB port, this pin will output a voltage of 3.3VDC. This pin can also be used to power the Photon directly (max input 3.3VDC). When used as an output, the max load on 3V3 is 100mA. NOTE: When powering the Photon via this pin, ensure power is disconnected from VIN and USB.


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@rickkas7 Dang… That’s likely what I did when I think about it. I should have known better and read the datasheet thoroughly as I thought it was odd that those other threads didn’t mention anything about just that.

I have a component that needs 3.3V (a RA8875 based screen), so I already had 3.3V available. I also need to drive some LEDs at 12V, so I used a regulator to step down and thought that would go smooth. I’ve now added a separate 5V regulator that I use to power the Photon and it’s rock solid.