When we classify materials based on their electrical properties, we say they are either good or bad conductors of electricity. For example, copper is a good conductor, whereas rubber is a bad conductor of electricity. Further, we classify materials as conductors, semiconductors, and insulators.
- Conductors constitute those materials that allow electricity to pass through them.
- Insulators are the opposite of conductors because they do not allow the flow of electricity.
- Semiconductors lie somewhere between conductors and insulators.
Research has shown that insulators can be made to function as conductors of electricity when you apply a specific amount of electricity to them. The minimum voltage at which an insulator starts conducting electricity is known as breakdown voltage and this process is known as Breakdown. Different materials have different breakdown voltages depending on their physical properties.
So what is breakdown voltage?
Breakdown voltage, also known as dielectric strength, is the minimum voltage or electrical force required to change the electrical properties of any object. So, the voltage at which an insulator starts behaving like a conductor is the breakdown voltage.
How does the transformation happen?
Electric conduction is possible only if the materials contain mobile electric charges. An insulator does not have any free mobile charges. Therefore, they do not conduct electricity. So even if we apply a potential difference across the insulating material, the current will not flow.
However, when the applied potential difference value increases beyond specific levels, the electron pairs can break, leading to the start of the ionization process. As a result, the material acquires free mobile charges, and they start moving from the positive to the negative terminal, resulting in an electrical flow.
This process is referred to as the ‘Electrical Breakdown’ of the material, and the voltage at which this happens is known as the breakdown voltage. Generally, the breakdown voltage value is not easily determinable. It is not a realistic constant, like the melting point of any substance. Thus, the breakdown voltage is often mentioned as a statistical average. Manufacturers usually provide the Average Breakdown Value of the material.
Breakdown voltage is denoted in Kilovolts per inch. The material with a higher breakdown voltage value is considered a better insulator. For example, porcelain has an average breakdown voltage of around 100 kilovolts per inch. On the other hand, glass has a breakdown voltage 20 times higher than porcelain. So, glass is a better insulator than porcelain.
Applications of Breakdown Voltage
Breakdown voltage has many applications, but we will restrict our discussion to the concept of breakdown voltage in an AC (Alternating Current) voltage stabilizer. First, however, we need to understand the concept of Diode Breakdown Voltage.
What is Diode Breakdown Voltage?
Diodes are semiconductors, and we have seen that semiconductors have the properties of conductors and insulators. For example, a PN junction diode contains a bandgap that allows the exchange of charge carriers. So when you apply a forward bias, the current flows in a forward direction, leading to conduction. Therefore, there should be no conduction when you apply a reverse bias. But, the presence of minor charge carriers, a small amount of reverse current flows through the diode. It is known as leakage current.
This leakage increases the junction barrier width. So when you gradually increase the reverse bias voltage, you can observe a rapid flow of reverse current. This point is known as junction breakdown, and the corresponding voltage is the PN junction breakdown voltage or Reverse Breakdown Voltage. So now, we come to the concept of Zener Diode.
What is the Zener Diode?
The Zener Diode is a perfectly doped PN junction diode that works in the breakdown voltage region without damaging itself. So a Zener diode is also known as a breakdown voltage diode and is primarily used as a voltage regulator or stabilizer. The prime function of a Zener Diode is to provide a constant voltage from a wildly fluctuating voltage source.
How does the Zener Diode work?
(VZ – Zener Diode, RS – Dropping Resistor, and RL – Load Resistance)
The Zener Diode is permanently connected across the fluctuating input voltage source through the dropping resistor having resistance RS.
As the input voltage increases, the Zener diode resistance decreases, resulting in high current flow through the diode. As a result, a significant voltage drop occurs across the dropping resistance RS. Therefore, it helps to maintain the output voltage drop across RL at a constant value.
Similarly, when the input voltage value decreases, the current passing through the Zener diode decreases, resulting in a small voltage drop across RS. It ensures the maintenance of a constant voltage across RL.
Therefore, the output voltage remains constant irrespective of the input current voltage. So a Zener Diode acts as a voltage regulator or voltage stabilizer. It explains the functioning of a voltage stabilizer.
Conclusion
Input voltage values can fluctuate, leading to damaging electrical equipment. The voltage stabilizer uses a Zener Diode and works on the breakdown voltage concept to ensure constant output voltage. Thus, it protects your expensive electrical equipment like refrigerators, televisions, and air conditioners from damage.