Question

In which bias can a zener diode be used as voltage regulator?

Answer 1

Zener diode is a silicon semiconductor chip that allows the current to travel either in the forward or in the reverse direction. The diode consists of a rare, heavily doped p-n junction engineered to work in the reverse direction when a specified voltage is reached.

Complete answer:
Zener diodes are commonly used to control the voltage through narrow circuits as voltage references and as shunt regulators. When attached to a variable voltage source in parallel such that it is reverse biased, a Zener diode conducts when the voltage exceeds the reverse breakdown voltage of the diode.

As a standard general-purpose diode consisting of a silicon PN junction, the Zener diode acts like a normal general-purpose diode and when biased in the forward direction, which is anode positive with respect to its cathode, it behaves much like a normal signal diode passing the graded current.

However unlike a traditional diode that when reverse biased, blocks any current flow through itself, that is, the Cathode becomes more positive than the Anode, the zener diode starts to conduct in the reverse direction as soon as the reverse voltage approaches a predetermined value.

This is because a phenomenon called Avalanche Breakdown happens in the semiconductor depletion layer as the reverse voltage applied through the zener diode reaches the device's rated voltage, and a current begins to flow through the diode to reduce this voltage rise.

Note: The voltage point at which the voltage becomes constant around the zener diode is called the "zener voltage," and this voltage will range from less than one volt to a few hundred volts for zener diodes. Zener diodes are used for voltage control as reference components, surge suppressors, and for switching applications and clipper circuits. The load voltage is equal to the output voltage of the diode. The series resistor limits the current through the diode and reduces the excess voltage when the diode is running.