I-V Characteristics of LED

Introduction

LEDs have grown over the years to be the most widely used semiconductor diode. The secret to their success lies in having a cluster of different functions and applications. When connected in a forward-biased condition, they are capable of emitting either visible light or invisible infrared light. In simple words, LEDs can be described as a device that converts electrical energy into light energy. LEDs come with a wide range of applications including traffic lights, indicator lights on electronic equipment and appliances.  Let us discuss LEDs and IV characteristics of LEDs in detail. 

What is an LED? 

An LED is a type of semiconductor light source that is capable of emitting light when an electric current is passed through it. We can refer to LEDs as specialised types of diodes that have electrical characteristics similar to that of a PN junction diode. In other words, LED is a kind of a diode that will only pass current in its forward direction and block the flow of current in the reverse direction. When this forward current is passed through them, LEDs emit a fairly narrow bandwidth of either different coloured wavelengths of visible light, infra-red light used in remote controls or a laser-like light. LEDs are proven to be the most visible type of diode. 

Every semiconductor diode we know and use is represented by a unique symbol. Similarly, LEDs are also represented by a unique symbol. The symbol of an LED bears resemblance to that of a PN junction diode except for an arrow pointing away from the diode. This arrow is an indication that the diode is emitting light. The IV characteristics of an LED are identical to a diode with a forward biased condition. 

How do LEDs Work? 

LEDs emit light by the mechanism of spontaneous emission. Semiconductors, like an LED, are characterised by having two energy bands – conductor band and valence band. The conductor band is the band of higher energy level and valence bands are lower energy bands. The region between conductor band and violence band is called the ‘band gap’.  Light energy is produced when an electron jumps from the high energy band i.e., conductor band, and falls into the lower energy band i.e., valence band. 

It should be noted that LEDs are current-dependent devices, which means they require a passage of current to flow through them in order to emit any form of light. The light output intensity of an LED is directly proportional to the forward current flowing through it. In other words, the higher the current flowing through an LED, the higher will be the output intensity of light. A series resistor is used to make an LED ‘current limited’, this protects the LED from excessive current flow. If a resistor is not placed between the LED and the power source, it will be instantly destroyed due to the passage of too much current. 

I-V Characteristics of an LED

I-V Characteristics are nothing but the current-voltage characteristics of an electrical component. In other words, they represent the behaviour of an electronic component at various values of applied voltage. The IV characteristics of an LED represent a relationship between the current passed and voltage applied across it. 

Represented in form of a graph, IV characteristics of LED provide valuable information pertaining to resistance and the operating region of the LED. IV characteristics of the  LED can help break down where and how it can be used in an electric circuit. On the IV graph of LED, the Voltage (V) is presented on the x-axis being an independent variable due to its ease of control as opposed to the current. That leaves us with current expressed on the y-axis. 

IV Graph of LED

IV graph of LED is a representation of the relationship between the current flowing through the LED as a function of the voltage across it. 

Points to be observed from the IV graph of LED: 

• The forward voltage of an LED is equal to the band gap. It increases in ascending order from red to violet. 
• For the visible spectrum energy gap of semiconductors is from 1.8 eV to 3 eV with Red before 1.8 eV and violet after 3 eV.
• It is not recommended to power LEDs in parallel as it is a particularly bad idea when the colours are mixed. For example, if red, green, and blue LEDs are connected in parallel on a 2.0V supply, it would result in
  • Red – 44mA
  • Green – 12mA
  • Blue – 3mA
• Red ends up hogging the majority of the current 
• The lowest forward voltage is seen in Infra-red LEDs

Conclusion

Owing to their numerous advantages, the use of LEDs can be seen everywhere from LED screens, energy-efficient lights to infra-red lights. The I-V characteristics of LEDs are important to understand in order to design a circuit that will work with the LED and make sense of how to make the best out of LEDs.

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