The electronic appliances in your household depend on their circuitry to function. These electrical circuits are designed in a way to let electricity flow in the appropriate direction for their various uses. Controlling the flow of electricity can be complicated given the different purposes electricity serves. That's where diodes come in.
Diodes are used to let electricity flow in a single direction through a circuit. Zener diodes differ from other types of diodes in that, when you connect them in the reverse direction in a circuit, such that current flows the other way across a diode, they let a small leakage current flow. This is a type of current that flows to the ground to prevent it from affecting other parts of the circuit as well as preventing damage to the diode itself.
You can use diodes such as the Zener diode in converting between alternating current (AC) and direct current (DC). AC current changes between flowing in one direction and flowing in the other while DC current only moves in one direction. You can find bridge rectifiers, or rectifier diodes, in many of these electrical setups.
Rectifiers can convert AC to DC current by either letting only one direction, positive or negative, of current flow through, or by converting one direction of the AC current cycle to the other direction. Rectifiers convert between the DC power supplies that transport electricity across long distances to the AC power that is found in most household appliances.
Zener Reverse-Breakdown Voltage
These characteristics let Zener diodes have a definite reverse-breakdown voltage. This is the voltage at which the diodes begins to conduct current in the reverse direction, and it's one difference between Zener diode and rectifier diode setups. These diodes have a defined voltage drop that doesn't change much over a range of input voltages.
As soon as you increase the voltage in the reverse direction for a Zener diode to the point where it reaches the breakdown voltage, the current flows through the diode. The series resistor of the diode governs the maximum value of the current before it stabilizes to a constant value. This value then remains constant no matter how much you change the input voltage.
If you increase the voltage to a value greater than the breakdown voltage, a voltage drop will form across the resistor. The current would to flow through the diode, and the device connects to the ground, shortcircuiting the diode. This would detach the load from the supply and regulate the voltage.
Zener Diode Applications
For these reasons, Zener diodes are well-suited for purposes of regulating voltage in circuits. You'll find these characteristics of Zener diodes in applications of voltage regulation, surge suppressors and clipper circuits.
Zener diodes in clipper circuits can change the shape of AC current to limit either its forward or reverse cycles. Zener diodes prove useful for regulating voltage in different circuits when there's too much or too little. The simplicity of their design and use makes them ideal candidates for converting voltage.
Like Zener diodes, rectifiers use P-N junctions, semiconductor materials that let current flow in only one direction. These are engineered using p-type semiconductors next to n-type semiconductors with a "p" side that has extra holes, places of no electrons, that are positively charged. In contrast, the "n" side has more electrons in its outer shells, making it negatively charged.
These semiconductor materials are made of metals like gallium or metalloids like silicon, the primary material that comprises Zener diodes, mixed with other elements like phosphorous. The placement between these atoms allows current to flow, and you can find bridge rectifiers controlling a wide range of currents through these designs.
About the Author
S. Hussain Ather is a Master's student in Science Communications the University of California, Santa Cruz. After studying physics and philosophy as an undergraduate at Indiana University-Bloomington, he worked as a scientist at the National Institutes of Health for two years. He primarily performs research in and write about neuroscience and philosophy, however, his interests span ethics, policy, and other areas relevant to science.