What Is Knee Voltage?

Are you curious to know what is knee voltage? You have come to the right place as I am going to tell you everything about knee voltage in a very simple explanation. Without further discussion let’s begin to know what is knee voltage?

Knee voltage is a term often encountered in the world of electronics, particularly when dealing with semiconductor devices like diodes. It plays a crucial role in defining the operating characteristics of these components. In this blog, we will explore what knee voltage is, how it impacts semiconductor devices, and its significance in the field of electronics.

What Is Knee Voltage?

Knee voltage, also known as the threshold voltage or cut-in voltage, is a critical parameter in the operation of semiconductor devices, especially diodes. It represents the voltage level at which a diode starts conducting electric current in the forward-biased direction. To put it simply, it’s the voltage at which a diode “turns on.”

Key Points About Knee Voltage:

  1. Activation Threshold: Knee voltage is the minimum voltage required to overcome the energy barrier at the junction of a semiconductor diode and allow the flow of electric current.
  2. Semiconductor Behavior: In semiconductor materials like silicon and germanium, which are commonly used in diodes, the behavior at the knee voltage is essential. Below the knee voltage, the semiconductor behaves as an insulator, blocking the flow of current. Above the knee voltage, it behaves as a conductor, permitting current to pass through.
  3. Forward-Biasing: To reach the knee voltage, the diode must be subjected to a forward-biased voltage, meaning the positive terminal of the voltage source is connected to the diode’s anode, and the negative terminal is connected to the cathode. This arrangement reduces the energy barrier at the junction.
  4. Varies by Diode Type: Different types of diodes, such as silicon, germanium, and light-emitting diodes (LEDs), have varying knee voltages. Silicon diodes typically have a knee voltage around 0.7 volts, while germanium diodes have a lower knee voltage of around 0.3 volts.

Significance In Electronics

  1. Rectification: The knee voltage is crucial for diodes used in rectifier circuits. It ensures that current flows in only one direction, allowing the conversion of alternating current (AC) into direct current (DC).
  2. Voltage Clipping: In electronics, diodes are often used for voltage clipping, limiting the voltage level in a circuit. The knee voltage determines the point at which the diode starts conducting and “clips” the excess voltage.
  3. LED Illumination: In light-emitting diodes (LEDs), the knee voltage is essential for determining the voltage at which the LED begins emitting light. This property is critical in various applications, from indicator lights to display screens.
  4. Transistor Biasing: In transistor circuits, diodes are often used for biasing purposes. Understanding the knee voltage is essential for setting the correct biasing conditions and ensuring proper transistor operation.


Knee voltage is a fundamental concept in electronics, particularly when working with semiconductor diodes. It defines the voltage level at which these devices transition from being non-conductive to conductive in the forward-biased direction. By understanding knee voltage and its implications, engineers and electronics enthusiasts can design circuits that function as intended, whether it involves rectification, voltage clipping, LED illumination, or transistor biasing. This understanding of knee voltage is essential for harnessing the full potential of semiconductor devices in the world of electronics.


Why Is It Called Knee Voltage?

The minimum amount of voltage required for conducting the diode is known as “knee voltage” or “cut-in-voltage”. The forward voltage at which the current through PN junction starts increasing rapidly is known as knee voltage.

What Is Knee And Breakdown Voltage?

The knee voltage or cut-in voltage is the forward voltage at which the current through the junction begins to rapidly increase. Break down voltage is the reverse voltage at which the P-N junction of a diode fails due to a sudden increase in reverse current.

What Is Knee Voltage Formula?

Knee point voltage of the current transformer is; Vkp = K * If/CTR * (RCT + RL + RR)

What Is Knee Voltage In Zener Diode?

When the applied voltage is more than the barrier potential, the resistance is small (ideally 0) and the current increases rapidly. This point is called the Knee-point or turn-on voltage or threshold voltage (Fig. 2-b). This voltage is about 0.3 volts for Ge diodes and 0.7 volts for Si diodes.

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