p-n junction diodes

Special purpose p-n junction diodes: LED, photodiode, solar cell, and Zener diode and their characteristics, Zener diode as a voltage regulator


A light-emitting diode (LED) emits visible light when forward biased. Light-emitting diodes are not produced using silicon or on the other hand, germaniums yet are made by utilizing components like gallium, phosphorus, and arsenic. By fluctuating the amounts of these components, it is conceivable to create the light of various wavelengths with colors that incorporate red, green, yellow and blue. For instance, when an LED is produced utilizing gallium arsenide, it will produce a red light. On the off chance that the LED is made with gallium phosphide, it will deliver a green light.

Characteristics of LED

  1. Low voltage
  2. Longer life (over 20 years)
  3. Fast on-off exchanging


A photograph diode is a reversed silicon or germanium p-n junction in which switch current increments at the point when the intersection is presented to light. The reverse current in a photo-diode is legitimately relative to the power of light falling on its p-n junction. This implies more noteworthy the power of light falling on the p-n junction of photo-diode, the more noteworthy will be the reverse current.

Characteristics of Photo-diode:

  1. Reverse current-Illumination curve.
  2. Reverse voltage-Reverse current bend

Solar cell:

A Solar cell, or photovoltaic cell, changes over light devoured in a p-n junction clearly to control by the photovoltaic impact. In a few cases, the term solar cell is put something aside for gadgets proposed unequivocally to get energy from sunlight, while the term photovoltaic cell is used when the light source is vague.

Characteristics of Solar cell:

Photocurrent in p-n junction solar cells streams in the diode reverse inclination heading. In obscurity, the solar cell goes about as a diode. In the light, the photocurrent can be thought of as a steady current source, which is added to the I-V characteristics for the diode. The connection between the dim and light current in a photovoltaic cell has appeared in the graph at the left.

Zener diode:

A Zener diode is a sort of diode that grants current not just the forward way like a typical diode, yet additionally in the reverse direction if the voltage is bigger than the breakdown voltage it called as “Zener knee voltage” or “Zener voltage.”

Characteristics of Zener diaode:

The Zener diode’s breakdown characteristics are dictated by the doping procedure. Low voltage Zeners under 5V work in the Zener breakdown extend. Those intended to work in excess over of 5 V work for the most part in torrential slide breakdown go. Zeners are accessible with voltage breakdowns of 1.8 V to 200 V. This bend outlines the base and most extreme scopes of current activity that the Zener can adequately keep up its voltage.

Zener diode as a voltage regulator

How about we guess that we have an information voltage of 12 Volt, and we need to confine the output voltage to 7.5 Volt. At that point, we pick a 1N47377.5V Zener diode. On the datasheet given, we can see that IZT= 34mA, which is the base current required for coming to Vz, and IZM=121 mA is the greatest admissible current. A decent working point is IZ=80 mA, close to the center of the range. As such, the Zener diode worked in this area will have a generally consistent voltage crosswise over it, estimation of current through the gadget. This allows the Zener diode to be utilized as a voltage regulator.


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