Getting more current through a BJT

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?)

1. Is there a better or more efficient setup to perform essentially the same function?

Thanks!

• 750mA out of coin cells?! That is a very short-lasting, expensive solution, and coin cells usually aren't even designed for such extremely high currents! Jul 3, 2018 at 1:06
• And aside from the LEDs, the NE555 would already be a waste of energy that I wouldn't recommend running off coin cells, as it would eat through these in no time. Jul 3, 2018 at 1:08
• "npn and pnp transistors" - do you think you could be just a little more specific? Jul 3, 2018 at 1:13
• I give you minutes at most - let's say a coin cell has a rated capacity of 200 mAh at small discharge currents until it drops to 2V. At 750 mA, my rough estimate for an upper limit of how much you can actually get from that coin cell is 10% - so, 20 mAh, or 20/750 h worth of operation; that's but 16 minutes. I doubt it's that much - internal resistance will cut you off much earlier. Jul 3, 2018 at 1:29
• I mean, it's your money, and whilst I do have environmental concerns about this, there's probably good reasons you want these coin cells – problem really is: these coin cells really aren't designed to deliver 750 mA, and that means their internal resistance will eat up most energy. If you want a more effective circuit, replace with a different type of battery. (measure the voltage across the coin cells when connecting LED + R across them; it'll be below 6V. How far below is defined by the internal resistance) Jul 3, 2018 at 1:50