Switching diode tutorial

What is Switching Diode? – Characteristic, Symbol, Definition

Switching Diode

Switching Diode (also called a Pulse Diode, Schottky Diode) – semiconductor diode used in pulse (discrete) systems. It mainly operates in switching configurations, which generate a pulse of only one sign (+), forward-bias. Depending on the application, switching diode can also operate as a simple rectifier diode,transient-voltage-suppressor or detection diode). It is characterized by a very fast operation rate (measured in nanoseconds, whereas for higher voltages – microseconds).

Most sought after parameters of switching diode, operating as a switching device are as follows:

  • Very low resistance in the forward bias and very high resistance in the reverse bias,
  • Switching process of the diode should occur as soon as possible (the least possible delay and no distortion of pulses).
switching diode symbol

Fig. 1. Switching Diode symbol

Switching Diode – Division

  • Fast switching diodes – they are manufactured with application of semiconductor materials with a wider band gap (e.g. Gallium Arsenide (GaAs): trr < 0,1ns). Schottky diodes have significantly shorter switching times (small junction capacity Cj values) compared to regular semiconductor diodes (trr of 100ps), which is due to their junction construction”M-S” junction capacity,
  • Low decay time diodes (also called step-recovery diode) – in this kind of diodes, storage of charge has a crucial impact on the diode operating speed. It is used to generate rectangular pulses (tf decay time must be very small).

Switching Diode – Limiting parameters

  • IFmax – maximum constant bias,
  • IFMmax – peak, maximum permissible diode bias,
  • VRmax – maximum constant reverse voltage,
  • VRMmax – maximum peak reverse voltage,
  • Tj – permissible junction temperature.

Switching Diode – Static and dynamic parameters

  • VF – forward voltage at a determined IF forward current (the higher the current, the greater the charge is stored on the pn junction diode basis and the defusing process is slower)
  • IR – reverse current at a given VR reversing voltage (the higher the current, the faster the charge that is stored in the junction will be unloaded, diode will switch faster)
  • Capacitance of the diode (at determined reverse voltage and frequency),
  • trr – duration of diode switch (occasionally, instead of trr time, Qrr switching charge that is accumulated in connector is given).

Switching Diode – Characteristic

Characteristic of switching diode is shown below on Fig. 2.

Switching Diode

Fig. 2. Illustration of the of diode switching process

Switching Diode – Applications

Short switching times of the Switching Diodes are sought after in many applications. Some of the most typical ones include:

  • Voltage clamping,
  • High speed rectifying and switching circuits,
  • Reverse current and discharge protection,
  • Switched-mode power supplies (as a rectifier).

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