Power transistors are big bulky because they have to deal with a large amount of current in a very short amount of time. They are the fastest of all the transistors.
Heat is the biggest enemy of the transistor. As silicon is heavily dependent on temperature. As the die temperature increases the more sensitive it becomes. And at a certain point, it burns out. At the moment of burning there is a short which generates so much heat that the silicon just burns itself off.
Even the TIP3055 can only handle instantaneous current pulses for a very short amount of time. If that same transistor is put under a continuous load it will burn out in a few instances.
If we look at the derating curve of any power transistor. We will find out that they are only good for up to 1Amps of DC operation. And even at 1 Amp, it will need a sizeable amount of aluminium heatsink.
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