3. $v_L = 16V$, $R_1 = 1k\Omega$, $R_2 = \infty \Omega$, $R_3 = 100\Omega$, $R_4 = 50\Omega$. forward bias voltage drop of the LED is 1.8V, amplification factor $\beta$ of the transistor is 100, and $V_{BE} = 0.7V$, $V_{CE} = 0.2V$ in saturation:
1) [5pts] Find the minimum value of $v_{in}$ for saturation of the transistor.
[5pts] Find the minimum value of $v_{in}$ to turn on the LED if it requires 100mA.
[5pts] Find the minimum value of $v_{in}$ to turn on the LED if it requires 100mA and $R_2 = 10k\Omega$, $R_3 = 1k\Omega$, $R_4 = \infty \Omega$.
