Question

To what value can RE be reduced without transistor going into saturation. Given : Vcc = 5V, Rc = 1kΩ, RB = 22kΩ, RE = 2.2kΩ, -VEE = -5V.

Answer 1

Let $\beta = 100$ and $V_{RE} = 3.9 V$

$I_E = \frac{V_{EE}}{R_E + \frac{R_B}{\beta}} = 2.06 mA$

$V_C = V_{CC} - I_CR_C = 2.94 V$

At saturation, $V_{C(sat)} = V_{E(sat)}$

$I_{C(sat)} = \frac{V_{CC}-V_{C(sat)}}{R_C} = 10 mA$

$(R_{E})_{min} = \frac{V_{RE}}{I_{E(sat)}} = 390 \Omega$

$\Delta R_E = 2200 - 390 = 1810\Omega$