What is the harm in applying too much current to the base of a NPN transistor when switching power?

by piojo   Last Updated January 14, 2018 08:25 AM

Background: I'm using a NPN transistor (TIP-122) to switch power to a ceramic resistor (i.e., a heater). I'm trying to finalize the circuit and move it from breadboard to perfboard. I will want to periodically swap the heater. One heating element draws 0.58A (at 12V), the other will draw 5A (at 5V).

If I choose a resistor for the base such that the transistor is saturated and applying enough current for the high power heater, will it cause damage when used with a lower power output? Or is the base resistor only present to protect the signal input (which is only designed to supply a tiny current)?

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