I built the following circuit. +3.3V GPIOs and +5V driven by an RPi Zero. Common-anode RGB LED wired to three IRLB3034 MOSFETs. These have Vgs(th)-min/max of 1V/2.5V.
The GPIOs are supposed to switch the MOSFETs to drive the LEDs on the 5V rail. Each LED is supposed to pull about 700 mA.
- The red LED works perfectly.
- The green LED was turning on as soon as the RPi was connected to power. I could stop this by shorting the gate to ground, but it would slowly build up again. Once the GPIO pin was explicitly set to 0 it would also stop. I "solved" this with a 100 Ω resistor from its gate to ground. Not really sure why this works.
- The blue LED doesn't fully turn on. If I apply 5V to the gate it does, but 3.3V just doesn't cut it (maybe 10% brightness).
- I've misunderstood something about the MOSFETs?
- The blue MOSFET is broken?
- Poor construction. I made this using an AdaFruit protoboard, big wires for the high-current and lots of solder. Have checked again and again for shorts.
- Something else??
- The 100 Ω resistor I added only for the green LED, and have now added to the diagram.
- This is the LED: link and datasheet
- The LED voltages are R: 2.5V, G: 3.6V, B: 3.6V.