Final answer:
Zener diodes are primarily utilized in power supply circuits to maintain a constant voltage by acting as voltage regulators, which enables them to uphold a specific voltage level across a load.
Step-by-step explanation:
Zener diodes are special types of diodes which not only allow current to flow in one direction like typical diodes but also can conduct in the reverse direction when a certain specified reverse voltage known as the Zener breakdown voltage is reached. This unique feature of the Zener diode makes it especially useful in maintaining a constant voltage across a load.
Zener diodes are most commonly used in power supply circuits to provide a regulated output voltage. They act as voltage regulators by maintaining a constant voltage level even when the supply voltage fluctuates or the load current changes.
In summary, the Zener diode is an excellent candidate for voltage regulation in power supply circuits due to its ability to conduct in reverse at a specific threshold voltage, thus clamping and regulating the voltage to a set value. Therefore, the correct answer to the question is:
c) Power supply circuits.