I'm trying to alternate between two 3W LEDs (forward current of 750mA, forward voltage of 3.6V). I've got a 555 set up in astable mode, and am driving the LEDs via npn and pnp transistors. In practice, the LED that's run via the pnp transistor gets more current when it's switched on compared to the LED connected to the npn, and I'm not sure why. I'd just do away with the transistors all together and let the 555 sink/source the current for me, but I believe it can only handle up to 200mA, and the LEDs need more. FWIW, I'm running this circuit off of 2 3V coin cell batteries, and when connected directly to the LEDs they are extremely bright.
So my questions are: 1. Is there a configuration change I can make to get more current through the transistors? (more base current maybe?)
- Is there a better or more efficient setup to perform essentially the same function?