I'm planning to switch 1A load at 5V with a TIP120.
Looking at it's power derating graph I see that at 5W case can be around 140C, but how can I tell if it will get hotter than that?
In the datasheet I see that thermal resistance junction to ambient is 62.5C/W so does this mean that it will dissipate 5 times that = 312.5C. That seems like a bit too much for such load.
If power dissipated is VCE * Ic (VCE is 4V for TIP120 at 5V collector voltage, right?), then this means 4 * 62.5 = 250C which is still a lot. I'm getting a feeling that this can't be right.
Also if I dissipate 4W and still provide 5W for my load, then that's almost 50% efficiency, thats horrible. I'm probably off on my calculations, I could really use some help..