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Types of Diode !

Types of Diode !
Types of Diode !
Types of Diode !
Types of Diode !
Types of Diode !

There are several more special diodes. These include:

  • Schottky diodes
  • PIN diodes
  • Varactor diodes
  • Tunnel diodes
  • Backward diodes

Their principles of operation and areas of application are described in the following text.

Schottky Diodes:

In this diode, a metal is bonded with an n-doped semiconductor. This results in a threshold voltage of about 0.35 V and a characteristic that climbs sharply afterwards. Furthermore, the low voltage allows a faster switching time. This diode is employed in high frequency circuits as a fast switch in both analogue and digital engineering.

Types of Diode !

PIN Diodes:

The name PIN is derived from the order of the zones in the design of this diode. An intrinsically conducting zone, the i-zone, is introduced between the p-semiconductor and n-semiconductor. A capacitance arises. At low frequencies, this diode behaves like a conventional diode. At frequencies above 10 MHz, the effect of the capacitance of the diode is so strong that AC currents are allowed to pass through. The limiting effect is dependent on any superpositioned DC current.

Types of Diode !
Varactor Diodes:

This diode makes conscious use of the capacitance that is present in the reverse direction. By applying a voltage in the reverse direction, it is possible to vary the width of the depletion layer. This is the equivalent of changing the plate separation in a capacitor. As a consequence of this, the capacitance changes. The greater the voltage applied in the reverse direction, the smaller the capacitance. These diodes are able to change their capacitance by a very large amount.

Types of Diode !

 

Tunnel Diodes:

These diodes are made of very heavily doped germanium. This gives rise to a very narrow depletion layer. A very small voltage of about 10 mV in the forward direction already causes a current to flow, even though the depletion layer has not yet disappeared. The depletion layer is "tunnelled through". This current increases until it reaches a maximum value and then falls off again. This fall gives rise to a region of negative resistance. As the voltage increases further, the normal diode current takes effect. When reverse biased, no blocking properties are apparent. Amplifier stages and oscillators in the HF range can be constructed using these diodes. They can likewise be employed as fast switches.

Types of Diode !

 

Backward Diodes:

These germanium diodes are constructed in a similar manner to tunnel diodes, but are more lightly doped. They exhibit a weak tunnelling effect in the forward direction, but this is not made use of. There is no effect whatsoever in the reverse direction, so that even a very small voltage gives rise to a large current. Because of this behaviour, this diode is operated in the opposite direction or backwards. Backward diodes can rectify very small voltages and are employed in HF applications. The characteristic shows a comparison with a tunnel diode (dashed).

Types of Diode !

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