In the attached NE555 PWM circuit, how do I determine the value of the emitter resistors?

Thanks.

 

what is the current your drawing through the load, the maximum per transistor is 200mA,
these resistors will limit the current in the load in the transistors, try using 4.7 ohms at 1/4W

 

what is the current your drawing through the load, the maximum per transistor is 200mA,
these resistors will limit the current in the load in the transistors, try using 4.7 ohms at 1/4W

I am planning to PWM some table top photo lights that I built using LED's. There are a total of 8 strings of LED's, and each string is conducting 18mA, for a total of 144mA, so I suppose that I could get by with one 2N3904, but two would allow for some headroom. (I showed four transistors just as an example for discussion.) In the case of two, what should the value of the emitter resistors be, and please explain how you arrive at the answer.

Thanks.