Two Supply Emitter Bias Circuit:

From the stability point of view, this two supply emitter bias circuit is the best of all already discussed circuits, but it has one drawback that it requires two power supplies or batteries or it requires one-split supply (dc power supply with a central point available).

Applying Kirchhoff’s second law around the circuit loop starting from V_EE and containing R_E and R_B

and I_C ≈ I_E for most practical purposes

The above equation provides almost an exact expression for I_E. It can further be simplified by realizing that in most of the cases V_BE is negligible in comparison to V_EE. Also R_B is chosen quite small so that R_B/β is also negligible in comparison to R_E

So

The above equation may be used to calculate the value of I_E for rough calculations at first instance but for exact value of I_E the former expression be used.

The approximate expression for I_E also suggests that all the V_EE supply is dropped across emitter resistance R_E. Therefore, the emitter terminal E is at ground potential for all practical purposes.

The collector-to-emitter voltage, V_CE is given as

since emitter is practically at ground potential.

Thus point Q is established.

From the expression,

we see that emitter or collector current is independent of variation of temperature as β and V_BE do not appear in the said expression.

For this two supply emitter bias circuit stability factor is given as