In a BJT bias circuit using a voltage divider with emitter degeneration, what is the role of the emitter resistor?

• A. It sets the base voltage via a resistive divider.
• B. It provides negative feedback for stabilization against beta variations.
• C. It increases the collector current directly.
• D. It acts as a current source in the collector.

Answer: (B)

The emitter resistor provides negative feedback that stabilizes the bias against variations in transistor beta (and temperature). In a voltage-divider biased stage, the base voltage is set by the divider, but the emitter current flows through the emitter resistor, creating a voltage drop that raises the emitter voltage. Since the base-emitter voltage drop stays roughly constant, a larger emitter voltage reduces the effective drive (base-emitter forward bias) for further current increase, and a smaller emitter voltage makes it easier for current to rise again. This self-correcting action keeps the collector current from changing too much when beta or Vbe changes, so the operating point stays more stable.

This role is not about setting base voltage—the divider does that. It doesn’t directly increase collector current; it actually limits changes in current. It also isn’t acting as a collector current source—the transistor does that, with the emitter resistor shaping how sensitive the current is to transistor parameters.