I’m trying to confirm that the solution posted in https://electronics.stackexchange.com/a/60868 will work for my application.
I have four yellow LEDs with a 2v drop (yellow) and 30mA max current I’d like to control via a single low current MCU GPIO pin with 3.3v logic. I’d like to pull from the unregulated power supply fed from USB or 3xAAA batteries in series (~4.5v).
If VIN measures 4.5-5v, with the base either 0v or 3.3v, emitter at 2.6v, I’m getting ~24 ohms needed to limit the LEDs to 25mA each (100mA total). This is assuming 700mv BE drop.
Does this work with saturation and everything that entails this configuration? I’m still very new to this, but I’m trying to setup the transistor as a current amplifier so that the GPIO pin stays well below 12mA and the fluctuating unregulated VIN can be used to feed to current for the LED load.