Objective: Consider a simple constant-voltage reference circuit and design the value of resistance required to limit the current in this circuit.

Consider the circuit shown in Figure 1.45. Assume that the Zener diode breakdown voltage is $V_{Z} = 5.6 V$ and the Zener resistance is $r_{z} = 0$ . The current in the diode is to be limited to 3 mA.

Question

Objective: Consider a simple constant-voltage reference circuit and design the value of resistance required to limit the current in this circuit.

Consider the circuit shown in Figure 1.45. Assume that the Zener diode breakdown voltage is [latex]V_{Z} = 5.6 V[/latex] and the Zener resistance is [latex]r_{z} = 0[/latex]. The current in the diode is to be limited to 3 mA.

Accepted Answer

As before, we can determine the current from the voltage difference across R divided by the resistance. That is,
[latex]I = \frac{V_{P S} − V_{Z}}{R} [/latex]
The resistance is then
[latex]R = \frac{V_{P S} − V_{Z}}{I} = \frac{10 − 5.6}{3} = 1.47 k \Omega[/latex]
The power dissipated in the Zener diode is
[latex]P_{Z} = I_{Z}V_{Z} = (3)(5.6) = 16.8 mW[/latex]
The Zener diode must be able to dissipate 16.8 mW of power without being
damaged.
Comment: The resistance external to the Zener diode limits the current when the diode is operating in the breakdown region. In the circuit shown in the figure,the output voltage will remain constant at 5.6 V, even though the power supply voltage and the resistance may change over a limited range. Hence, this circuit provides a constant output voltage. We will see further applications of the Zener diode in the next chapter.

Question 1.13: Objective: Consider a simple constant-voltage reference circ...

Related Answered Questions

Verified Answer:

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 Vγ = 0.6 V and rf = 10 Ω ...

Verified Answer:

Verified Answer:

Objective: Determine diode voltages. The reverse saturation currents of a pn junction diode and a Schottky diode are IS = 10^−12 A and 10^−8 A, respectively. Determine the forward-bias voltages required to produce 1 mA in each diode ...

Verified Answer:

Objective: Analyze the circuit shown in Figure 1.35(a). Assume circuit and diode parameters of VP S = 5 V, R = 5 kΩ, Vγ = 0.6 V, and vi = 0.1 sin ωt (V). ...

Verified Answer:

Objective: Determine the diode current and voltage characteristics of the circuit shown in Figure 1.28 using a PSpice analysis. ...

Verified Answer:

Objective: Determine the diode voltage and current for the circuit shown in Figure 1.28. Consider a diode with a given reverse-saturation current of IS = 10^−13 A ...

Verified Answer:

Objective: Determine the current in a pn junction diode. Consider a pn junction at T = 300 K in which IS = 10^−14 A and n = 1. Find the diode current for vD = +0.70 V and vD = −0.70 V ...

Verified Answer:

Verified Answer:

Objective: Calculate the built-in potential barrier of a pn junction. Consider a silicon pn junction at T = 300 K, doped at Na = 10^16 cm^−3 in the p-region and Nd = 10^17 cm^−3 in the n-region. ...

Verified Answer: