Semiconductor devices - diode

Introduction

Every technically literate person should know electronics. The vast majority of devices of modern electronics are made of semiconductor materials. According to this, in the framework of this article, I would like to talk about diodes. Of course, without knowing the basic properties of semiconductors, it is impossible to understand how the transistor works. But one acquaintance only with the properties of semiconductors is not enough. It is necessary to understand very interesting and not always simple phenomena.

Quick reference

The electric-hole transition (pn junction) is a transition layer between two regions of a semiconductor with different electrical conductivities, in which there is a diffusion electric field.
Diodes are semiconductor devices, the basis of which is the pn junction. The use of semiconductor diodes is based on a number of their properties, such as the asymmetry of the current-voltage characteristic, the breakdown of the electric-hole junction, the dependence of the barrier capacitance on voltage, etc.

Transition property used

• Rectifying - asymmetry of current-voltage characteristics
• Zener diode breakdown
• Varicap - barrier capacity
• Pulse - transients

We will get acquainted with them in more detail.
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Rectifier diodes

Rectifier diodes are designed to convert a variable signal into a constant.
Consider the principle of operation of the simplest half-wave rectifier on a semiconductor diode.

Description of work

Upon receipt of a primary source of alternating voltage, the diode will be open at a positive half-wave and closed at a negative one. As a result, a current will flow through the diode and the load resistance in a half-wave. the capacitor is charged to a value close to the peak one. When the voltage in the input circuit decreases, the diode is locked. In this case, the capacitor begins to discharge through the resistance of the load.
The disadvantage is that the rectifier voltage strongly depends on the resistance of the load and has a large amplitude of the ripple. Therefore, such rectifiers are used only for arrogant loads. For the formation of impulses amplitude limiters are used, which can be serial and parallel. In series diode limiters, the diode is connected in series with the load resistance.

Varicaps

A varicap is a semiconductor diode used as an electrically controlled capacitance.
These parametric diodes work in the opposite direction, on which the barrier capacitance depends. Thus, the varicaps are capacitors of variable capacitance, which is controlled not mechanically, but electrically, with a change in the reverse voltage.
Varicaps are mainly used for tuning oscillatory circuits. The simplest scheme for the inclusion of a varicap in an oscillatory circuit in the figure.

Description of work

Tuning the oscillating circuit to the resonant frequency can be done in two ways. Firstly, by varying the frequency of the alternating input voltage Uin to the circuit. Secondly, due to a change in the natural frequency of wo, which is caused by the inductance and capacitance of the oscillating circuit. By changing the magnitude of the reverse voltage Uobr., It is possible to adjust the capacitance of the varicap and, consequently, to change the resonant frequency of the circuit. Capacitor Cp is separable. It is necessary to prevent shunting of the varicap inductance.

Zener diodes

Zener diode is a semiconductor diode used to stabilize the voltage.
Plot corresponding to the electrical breakdown Uprob. on which the voltage is weakly dependent on the current, is working. When using a Zener diode to stabilize a constant voltage, it is switched on parallel to the load. Most often, the Zener diode operates in such a mode, when the source voltage is unstable, and the load resistance Rn is constant. To establish and maintain the correct stabilization mode in this case, the resistance Rogr. must have a specific value. To eliminate the temperature drift voltage is used in series diode. Such diodes are called thermocompensated zener diodes.

Pulse diodes

Pulsed diodes have a short duration of transients and are designed to work as switching elements. There are various types of pulsed diodes: floatable, point mesa-diodes, Schottky diodes.
Pulsed diodes are widely used as switching elements, i.e. devices that have two stable states: "open" when the resistance of the device is small and "closed" when it is large.
When using a diode as a key, various diode and diode-transistor circuits designed to work in digital equipment can be combined.

In custody

I apologize for the drawings, the elements of the schemes are not according to the guests (their ratio), but I think it will come down for a good example.
PS: Is it worth talking about transistors?