Switching diode (also called a Pulse diode) – semiconductor diode used in pulse (discrete) systems. It mainly works as a keying device, which transmits a pulse in only one bias, forward-bias. Switching diode can work as a simple rectifier (it depends on the application, also as transient-voltage-suppression and detection diode). It is characterized by a very high work-rate (measured in nanoseconds, whereas for higher voltages – microseconds). In case of diode, which is operating as a keying device, its high quality is determined by the following parameters:
- 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 can be divided into two types that are relevant for the application:
- Low switching time diodes – they are manufactured with application of semiconductor materials with a wider band gap (for example for Gallium Arsenide GaAs trr < 0,1 ns).
Schottky diodes have significantly shorter switching times (trr of 100 ps) caused by very low M-S junction capacity,
- Low decay time diodes (also called step-recovery diode) – in this kind of diode storage of charge takes place that has a crucial impact on the diode working speed. It is used to generate rectangular pulses (tf decay time must be very small).
Permissible limits for the Switching diode:
- IFMAX – the maximum constant bias,
- IFMMAX – peak, maximum permissible diode bias,
- VRmax – maximum constant reverse voltage,
- VRMmax – maximum peak reverse voltage,
- Tj – permissible junction temperature.
Characteristic parameters of static and dynamic Switching diode:
- VF – a 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 UR reversing voltage (the higher the current, the faster the charge that is stored in the database will defuse – 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).