What is the output voltage in Fig. 32-26a?

Question

Accepted Answer

For the 2N7000, the most important values are

[latex]V_{GS(on)} = 4.5 V[/latex]

[latex]I_{D(on)} = 75 mA[/latex]

[latex]R_{DS(on)} = 6 \Omega[/latex]

Since the input voltage swings from 0 to 4.5 V, the 2N7000 is being switched on and off.

The drain saturation current in Fig. 32-26a is

[latex]I_{D(sat)} =\frac{20V}{1 K\Omega } =20 mA[/latex]

Since 20 mA is less than 75 mA, the value of [latex]I_{D(on)}[/latex], the 2N7000 is biased in the ohmic region when the gate voltage is high.

Figure 32-26b is the equivalent circuit for a high-input gate voltage. Since the E MOSFET has a resistance of 6 V, the output voltage is

[latex]V_{out}=\frac{6\Omega }{1 k\Omega +6\Omega}(20 V)=0.12 V[/latex]

On the other hand, when [latex]V_{GS}[/latex] is low, the E-MOSFET is open (Fig. 32-26c), and the output voltage is pulled up to the supply voltage,

[latex]V_{out} =20 V[/latex]

Question 32.4: What is the output voltage in Fig. 32-26a?