I have this kind of trouble. I'm working on a project that implements several load (some relays, or motors, etc).
Or, more simple, I would light 6 LEDs in series, all togethers, with only a GPIO (let's say the PIN 0/11).
With only 1 led, ok, you use GPIO 0 + GND and all OK, current is very low. 6 Led can burn the PI.
So, I would connect an EXTERNAL power source to the breadboard. And not using the PI current.
How I need to link? Do I need a transistor (like the 2N2222) that acts as a switch?
PI GPIO 0 --> RESISTOR --> TRANSISTOR BASE
EXTERNAL POWER (9V in my case) --> TRANSISTOR EMETTITOR
TRANSISTOR COLLECTOR --> POSITIVE for the LEDs (or other load) ?
Otherwise, If i connect the GPIO 0 to the same line of 9v of the external power, I imagine that PI burns in 3-2-1 boom! or btw the circuit is closed and the loads function... no PI control...