I'm trying to use the 3.3V rail to power up 10 LED (20mA/LED).

I read that the raspberryPi could supply until 1A through this 3.3V rail, that's a lot more than needed when all the LEDs are powered on.

When I'm using the regular power supply of raspberry (2.5A, 5V) through usb, I somehow don't get enough current to light my LEDs: enter image description here

When I use my laboratory power supply with the same set up (2.5A, 5V) to power up the raspberry through usb, the leds light up correctly : enter image description here

I also tried with a phone power supply with the same set up again (2.5A, 5V) and it didn't work.enter image description here

In the end, I tried with an industrial power supply converter (230V to 5V, 3A) and it worked correctly : enter image description here

It seems that some of my power supplies don't deliver enough current.

I don't understand why there are such differences in behaviour, the power supplies are supposed to be the same technically.

Is there anything I could have missed about this 3.3V raspberryPi output ?

What could I do to check this power supplies ?

  • 2
    Some models of Pi can supply more than an amp on the 3V3 power rail. Which model Pi are you using? Also let's see photos of a setup you are using which does not work.
    – joan
    Commented Sep 17, 2019 at 15:46
  • I'm using thePi 3 model B+, I just added the pictures of the power supplies I used
    – A.Girafe
    Commented Sep 25, 2019 at 12:57

1 Answer 1


the power supplies are supposed to be the same technically

No, they simply have the same or similar maximum ratings.

A phone charger is intended for charging batteries. A supply intended for powering live electronics has to meet instantaneous demands and an arbitrarily fluctuating load that a charger does not -- and it might, in fact, it might be detrimental for a charger to do so.

If we consider the role of the phone charger less demanding, then this is sort of a quality issue: Which do you think needs to perform in a more demanding environment, your lab bench supply or your phone charger? I bet the former cost a bit more too. On the other hand, using that bench supply to just to charge your phone might be considered awkward because the bench supply is heftier and a waste of money since all you needed was a phone charger.

But the Pi is not a battery powered device which needs recharging.

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