I'm a beginner. I'm designing a battery powered LED flashlight with a dimmer. The flashlight will have 3 LEDs and the dimmer will be controlled by a PWM signal generated by a 555. The circuit is powered by 2 AA batteries (3V).
This is the LED part of the circuit:
So, my calculation is this: I'm applying a 3V signal through a 12k resistor, so the current being applied in the transistor base is 0,25mA. Since the 2N3904 (Q1) has a max hFE of 300, the current being sunk by the transistor is 75 mA. This current will be divided between the three LEDs, 25mA for each one, which is the rated current for this LED.
So, my questions are:
- Are my calculations correct? Is my circuit correct?
- This transistor has a hFE value between 100 and 300. I'm using 300 to be on the safe side. Is this correct?
- Am I at risk of destroying the transistor or the LEDs? If one LED burns, the current will be then divided between the other two (38 mA each)?
- Is this the most efficient way of powering these LEDs?