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 – 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 – 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).