The Bipolar Power Transistor Drive Circuit

7c(max) is the maximum anticipated collector current. h-pE is the minimum specified dc gain of the transistor. 

The last consideration is from which voltage to draw the base current. Since the base-emitter junction resembles a forward-biased diode, the maximum Vbe is 0.7 to 1.0 V. Ideally, a voltage source of 2.5 to 4.0 V is sufficient. If the base drive voltage source is too high, there will be a significant loss associated with driving the base. 

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