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).

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): t_rr < 0,1ns). Schottky diodes have significantly shorter switching times (small junction capacity C_j values) compared to regular semiconductor diodes (t_rr 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 (t_f decay time must be very small).

Switching Diode – Limiting parameters

• I_Fmax – maximum constant bias,
• I_FMmax – peak, maximum permissible diode bias,
• V_Rmax – maximum constant reverse voltage,
• V_RMmax – maximum peak reverse voltage,
• T_j – permissible junction temperature.

Switching Diode – Static and dynamic parameters

• V_F – forward voltage at a determined I_F forward current (the higher the current, the greater the charge is stored on the pn junction diode basis and the defusing process is slower)
• I_R – reverse current at a given V_R 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),
• t_rr – duration of diode switch (occasionally, instead of t_rr time, Q_rr switching charge that is accumulated in connector is given).

Switching Diode – Characteristic

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

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).