3 views

For the $\text{BJT Q}_1$ in the circuit shown below, $\beta=\infty, \mathrm{V}_{\mathrm{BEon}}=0.7 \mathrm{V}, \mathrm{V}_{\mathrm{CEsat}}=0.7 \mathrm{V}$. The switch is initially closed. At time $t=0$, the switch is opened. The time $t$ at which $\mathrm{Q}_1$ leaves the active region is

1. $10 \mathrm{~ms}$
2. $25 \mathrm{~ms}$
3. $50 \mathrm{~ms}$
4. $100 \mathrm{~ms}$