Powering 2 Amp PCB from Photon on board USB socket

Hey guys,

I’m designing a PCB that has a power consumption of 2 Amp at 5 Volts. The PCB has among other things, a Photon and a Neopixel LED strip. The strip is the current hunger devices that requires the 2 Amp.

I would like to power the PCB using the Photon’s on-board USB socket. Then I would use the VIN/GND pins to power the rest of the circuit.

Given that the Photon only requires 1 Amp, would I damage the Photon by passing through it 2 Amps?

@mebrunet you are powering your PCB from the Photon, right? How much current are you using in your board?


2A through a micro-usb connector is going to be a reliability issue.

Please consider turning this problem around, terminating the 5V 2A supply on your board, then supplying some of that via Vin to the photon.

There is a blocking diode on the photon that should protect your computer from damage by the external 5V supply, but you will also want to ensure that you don’t accidentally try and get a USB-connected computer to supply all 2A (the protection inside the computer should kick in, but better to avoid the problem than tempt fate.)


@sazp96 Yes - we’re exposing the Photon’s usb jack as the sole power entrance to our product. We then tap off the board’s Vin pin to drive a low power radio and a couple tiny smd leds. Altogether they pull max 150mA.

The only power related issues we experienced were in SoftAP mode, however our radio and leds don’t draw any power in SoftAP mode, so that was strictly an RF interference / ground loop issue. We resolved it using an external WiFi antenna.

I would agree with @AndyW and say not to pull 2A right off the USB. Most standard USB wall “chargers” are rated up to 1A, and I’m pretty sure most laptops limit the USB current output somewhere between 500mA and 1A.

Keep in mind that the Photon pulls ~300mA in transmission (possibly peaking higher) and should be factored into that limit.

That being said, if you only use your device with a specific USB power supply capable of of delivering 2.5 to 3 Amps, will it work…? I assume yes, but I’d verify the trace widths between the USB jack and the Vin pin.

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My concern was rooted more in using the USB connector to carry 2A - there is just not a whole lot of surface area on those puppies.

Fair enough - I’m not sure what they’re rated to…

We are currently using a power source that provides 2.5Amps --> that feeds a USB jacket rated for 3 Amps (on pin 1 and 5) --> connected to some capacitors that feed the PCB --> connected to the VIN/GND pins on the Photon.

It is all working fine (with the exception of SoftAP). I just wanted to see if we could use the Photon’s USB socket and reduce the complexity of the board. But I think the answer is no give our power requirements.

Thanks guys!

I think it would work, at least for a while; but I would counsel against relying on the on-module micro-usb jack for a 2A load.

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Let me clarify. In my current configuration I have an independed USB socket that is connected to the PCB. I’m not using the Photon’s USB socket.

So @AndyW, I totally agree. I need this thing to work for a lot longer than a while :slight_smile:

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