When creating electronic circuits for various purposes, semiconductor diodes are widely used. Initially, they were created as a replacement for tube counterparts and in comparison with their electric vacuum predecessor provided a significant gain in weight and size characteristics and consumed power.
It is known that in circuitry, the best results are obtained by using a specialized element base, which is optimized for a specific field of application. For modern electronics, one of the fundamental ways to define a field of application is the division into analog and digital technology. With regard to diodes: in the first case, a conventional rectifier element was used. In digital electronics, it is advisable to use the so-called. pulse diodes, structurally different from conventional ones.
Rectifier diode properties
The principle of operation of any diode is based on the formation of a potential barrier, the presence of which ensures the passage of current in one direction with minimal losses and blocking of its flow in the opposite.
In rectifier diodes, the barrier was formed as a pn junction of two directly interacting semiconductors with different types of conductivity. In addition, the rectification process itself usually involved working with relatively high currents. To increase the maximum value of this parameter, the developer increased the transition area.
This feature:
- allowed to work with moderate current density;
- provided low forward resistance;
- removed the problem of removing excess heat;
- suppressed the processes of degradation of the pn-junction and increased the service life of the diode.
At the same time, a large junction area led to an increase in capacitance, which inevitably worsened the frequency properties of the diode. Figure 1 shows the designation of a rectifier diode.
Features of pulse diodes
A pulse diode, on the other hand, has a small junction area to reduce capacitance, does not differ in high breakdown resistance for reverse voltage, not designed for high current and has an increased value reverse current. Figure 1 on the right shows its circuit designation, and Figure 2 shows its current-voltage characteristics and one of the options for the switching circuit.
One variant of the pulse diode, called the Schottky diode after its inventor, uses a potential barrier formed by a semiconductor-metal interface.
Thereby:
- the capacity is noticeably reduced, which can be further limited by a decrease in the transition area;
- additionally to 0.25-0.30 V, the threshold voltage value is reduced.
Structurally, a pulse diode most often has a typical cylindrical body shown in Figure 3.
Focal area of application of pulse diodes
Pulse diodes by their parameters are well suited for use in:
- high-speed logic circuits;
- sweep circuits of stroboscopic oscilloscopes;
- ultrashort pulse shapers.