# NPN Transistor Analysis: How is collector current determined?

I'm trying to understand NPN transistors by reading the chapter on them in Razavi's "Fundamentals of Microelectronics", and it says that collector current (Ic) is a function of the base-emitter voltage (Vbe):

$$I_c = I_s \cdot e^{\frac{V_{be}}{V_t}}$$

where Is and Vt are constants.

In the following section, the beta value is introduced and it states that the collector current is base current times beta:

$$I_c = \beta \cdot I_b$$

I'm confused whether Ic is determined by Vbe or Ib (or both?) since both these values can be controlled independent of each other using a resistor.

Can you give an explanation of how terminal currents and/or voltages are determined?

Pic for reference:

• Vbe and Ib are not independent. If you add a resistor in front of the base, the current through base will decrease, but so will the voltage across the base-emitter junction. – avakar Apr 3 '12 at 11:46