IR EMITTER CIRCUIT

 

           +5V                       555         +5V
            |                       TIMER         |
            /                   +-----------+     |
            \                  1|           |8    |
            / 10ohms   GND -----|GND     Vcc|-----+
            \                   |           |     \
            /                   |           |     /
            |                  3|           |     \ 2.2K
            +-------------------|OUT        |     /
            |                   |           |7    \
            |                   |      DISCH|-----+
            |                  4|-          |     \
IR LED  ||--+          +5V -----|R          |     /
       <||                      |           |     \ 200K
        ||--+                   |           |     /
            |                  2|           |6    \
            |               +---|TRIG  THRES|-----+------+
            |               |   |           |     |      |
            |               |   +-----------+     |      |
           GND              |                     |    ----- .1uF
                            |                     |    -----
                            +---------------------+      |
                                                         |
                                                        GND

How long will the parts survive. 555 timers can source and sink a lot of current. 

So, look at when the output is high, it is sourcing as much as it can in parallel with the 10 ohms to the IR led. The IR led drops about 1.6 v, so we have about 3.4v divided by 10 ohms is about 340 ma, and we have the current sourced by the 555, which could easily be 100 or more ma. The oscillator is designed for a nearly 50 % duty cycle, so we're probably only exceeding the IR led maximum current rating by something well over 50%.

When the 555 output is low, it will be clamping to something less than the IR led voltage, so the current sourced via the 10ohm will be fully dissipated into the 555. Now, if the 555 clamps to 1 volt, we will have 400 ma into that pin. This is a totally unnecessary power loss!