Chapter 3, Problem 3.13TYU

The transistor in the circuit shown in Figure 3.48 has parameters $K_n=4{\text{mA/V}}^{\text{2}}$ and $V_{TN}=0.8\text{V}$ , and is used to switch the LED on and off. The LED cutin voltage is $V_{\gamma }=1.5\text{V}$ . The LED is turned on by applying an input voltage of ${\upsilon }_I=5\text{V}$ . (a) Determine the value of R such that the diode current is 12 mA. (b) From the results of part (a), what is the value of ${\upsilon }_{DS}$ ? (Ans. (a) $R=261\Omega$ , (b) ${\upsilon }_{DS}=0.374\text{V}$ )

Figure P3.48