Voltage Regulation

Voltage Regulation is an important part in power design for electronic circuits as regulators are able to stabilize the voltage the circuits receive. This is especially important in high precision circuits where a stable power source is necessary for the circuit to operate properly. Voltage Regulators maintain a steady DC voltage within the regulator’s operating range.

Building a Voltage Regulator

Figure 1 shows the Voltage Regulator Circuit that is constructed in Lab 4. The key elements of the circuit are resistors, Bipolar Junction Transistors (BJT), a Zener Diode, and an Op-Amp. These components are connected in a specific topology to create the Voltage Regulator.

Figure 1: Voltage Regulator Circuit

Dr. Joseph Young

Reference Voltage

The Zener Diode is used to create a reference voltage. As noted in Horowitz and Hill’s The Art of Electronics¹, “When [a zener diode is] connected in parallel with a variable voltage source so that it is reverse biased, a Zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. From that point on, the low impedance of the diode keeps the voltage across the diode at that value.” The Zener Diode in Figure 1 is in parallel with the rest of the circuit, meaning that the diode is providing a reference for the Op-Amp and BJTs to use. According to the 1N5226 Zener Diode Datasheet², the zener diode that is used in this circuit has a nominal Zener (Breakdown) Voltage of 3.3V at 20 mA. While this value differs from what is found in practice, it dictates the reference voltage for the rest of the circuit. It is important to note that Zener Diodes often require a bias current. In the circuit diagram shown in Figure 1, the R3, 10 kΩ resistor is required to put the Zener Diode in breakdown mode.

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References

1) Horowitz, Paul; Hill, Winfield (1989). The Art of Electronics(2nd ed.). Cambridge University Press. pp. 68–69. ISBN 0-521-37095-7.
2) https://www.futurlec.com/Diodes/1N5226.shtml