Zener regulator

A non-ideal voltage source can be modeled by a series combination of an ideal DC voltage source, a resistance, and a small-signal voltage source. The small-signal source is included to represent the noise inherent in the source. This model is illustrated in the figure below:

In practice, connecting the non-ideal voltage source to a load may result in undesirable effects due to the noise voltage vo appearing across the load.

This problem studies such effects and how a Zener diode may be used to ameliorate the problem. Assume that VI=9.5 V, RIN=1 kΩ , and vi=50.0 mV.

In the figure above, calculate the DC output voltage VO , and the output noise voltage vo for two values of the load resistance.

1.For RL=2 kΩ , the value of VO (in Volts) is:

2.and the value of vo (in Volts, to at least 3 decimal places) is:

3.For RL=4 kΩ the value of VO (in Volts) is:

4.and the value of vo (in Volts, to at least 3 decimal places) is:

Now, we can insert a Zener diode into the circuit, as shown below. The Zener diode is a nonlinear device and a piecewise-linear approximation to its i-v characteristic is shown graphically below.

Again, we calculate vo (i.e. output noise) and VO (i.e. DC output voltage) for RL =2k Ω and RL =4k Ω for this new circuit.

Hint: Your first job here is to determine which of the three regions of the piecewise-linear characteristic of the Zener is the one containing the operating point: we suggest you sketch a load line, but be very careful about the signs. Once you have determined where the operating point is, you can model the Zener in the circuit with a series combination of an independent voltage source and a resistor.

5.For RL=2 kΩ the value of VO (in Volts) is:

6.And the value of vo (in Volts, to at least 5 decimal places) is:

7.For RL=4 kΩ the value of VO (in Volts) is:

8.And the value of vo (in Volts, to at least 5 decimal places) is:

9.What is the minimum value of RL , in Ohms, that guarantees that the circuit will operate this way?

by servomotor
July 28, 2020

We don't have the I-V curve approx. for the Zener diode. It probably give its Vz (at 1 mA in reverse) and the resistance value for that almost perpendicular segment which may be essential to solve the problem. Furthermore, that looks like a homework problem. Can't you sketch the circuit with the circuitlab simulator? You have a problem doing exactly that?

by vanderghast
July 28, 2020

I agree completely with @vanderghast's comment :)

What have you tried already? Where exactly are you stuck?

by mrobbins
July 28, 2020

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