Analysis of a Zener-Diode Regulator with a Load Consider the Zener-diode regulator circuit shown in Figure 9.12(a). The diode characteristic is shown in Figure 9.13. Find the load voltage vL and source current IS if VSS = 24 V, R = 1.2 kΩ, and RL = 6 kΩ.

Question

Analysis of a Zener-Diode Regulator with a Load
Consider the Zener-diode regulator circuit shown in Figure 9.12(a). The diode characteristic is shown in Figure 9.13. Find the load voltage [latex]v_L[/latex] and source current [latex]I_S ext{ if } V_{SS} = 24 ext{ V}, R = 1.2 ext{ k}\Omega, ext{ and } R_L = 6 ext{ k}\Omega[/latex].

Accepted Answer

First, consider the circuit as redrawn in Figure 9.12(b), in which we have grouped the linear elements together on the left-hand side of the diode. Next, we find the Thévenin equivalent for the linear portion of the circuit. The Thévenin voltage is the open-circuit voltage (i.e., the voltage across [latex]R_L[/latex] with the diode replaced by an open circuit), which is given by

[latex]V_T=V_{SS}\frac{R_L}{R+R_L}=20 ext{ V} [/latex]

The Thévenin resistance can be found by zeroing the voltage source and looking back into the circuit from the diode terminals. This is accomplished by reducing [latex]V_{SS}[/latex] to zero so that the voltage source becomes a short circuit. Then, we have R and [latex]R_L[/latex] in parallel, so the Thévenin resistance is

[latex]R_T=\frac{RR_L}{R+R_L} =1 ext{ k}\Omega[/latex]

The resulting equivalent circuit is shown in Figure 9.12(c).
Now, we can use Kirchhoff’s voltage law to write the load-line equation from the equivalent circuit as

[latex]V_T+R_Ti_D+v_D=0[/latex]

Using the values found for [latex]V_T ext{ and } R_T[/latex], we can construct the load line shown in Figure 9.13 and locate the operating point. This yields [latex]v_L = -v_D = 10.0 ext{ V}[/latex].
Once vL is known, we can find the voltages and currents in the original circuit.
For example, using the output voltage value of 10.0 V in the original circuit of Figure 9.12(a), we find that [latex]I_S = (V_{SS} - v_L)/R = 11.67 ext{ mA}[/latex].

Question 9.4: Analysis of a Zener-Diode Regulator with a Load Consider the...

Related Answered Questions

Analysis Using a Piecewise-Linear Model Use the circuit models found in Example 9.6 to solve for the current in the circuit of Figure 9.20(a). ...

Verified Answer:

Piecewise-Linear Model for a Zener Diode Find circuit models for the Zener-diode volt–ampere characteristic shown in Figure 9.19. Use the straight-line segments shown. ...

Verified Answer:

Analysis by Assumed Diode States Use the ideal-diode model to analyze the circuit shown in Figure 9.16(a). Start by assuming that D1 is off and D2 is on. ...

Verified Answer:

Load-Line Analysis of a Zener-Diode Voltage Regulator The voltage-regulator circuit of Figure 9.9 has R = 1 kΩ and uses a Zener diode having the characteristic shown in Figure 9.10. Find the output voltage for VSS = 15 V. Repeat for VSS = 20 V. ...

Verified Answer:

Load-Line Analysis Repeat Example 9.1 if VSS = 10 V and R = 10 kΩ. ...

Verified Answer:

Load-Line Analysis If the circuit of Figure 9.5 has VSS = 2 V, R = 1 kΩ, and a diode with the characteristic shown in Figure 9.7, find the diode voltage and current at the operating point. ...

Verified Answer: