Question 1.9: Objective: Determine the diode voltage and current in the ci...
Objective: Determine the diode voltage and current in the circuit shown in Fig-ure 1.28, using a piecewise linear model. Also determine the power dissipated in the diode. Assume piecewise linear diode parameters of V_{γ} = 0.6 V and r_{f} = 10 Ω
With the given input voltage polarity, the diode is forward biased or “turned on,” so I_{D} > 0 . The equivalent circuit is shown in Figure 1.31(a). The diode current is determined by
I_{D} = \frac{V_{PS} – V_{\gamma}}{R + r_{f} } = \frac{5 – 0.6}{2 \times 10^{3} + 10 } ⇒ 2.19 mAand the diode voltage is
V_{D} = V_{\gamma} + I_{D} r_{f} = 0.6 + (2.19 \times 10^{-3})(10) = 0.622 VThe power dissipated in the diode is given by
P_{D} = I_{D} V_{D}We then find
P_{D} = (2.19) (0.622) = 1.36 m WComment: This solution, obtained using the piecewise linear model, is nearly equal to the solution obtained in Example 1.8, in which the ideal diode equation was used. However, the analysis using the piecewise-linear model in this example is by far easier than using the actual diode I–V characteristics as was done in Example 1.8. In general, we are willing to accept some slight analysis inaccuracy for ease of analysis.
