Medium power rectifier diodes reference book. Rectifier diode: principle of operation and main parameters

A rectifier diode is a device that conducts current in one direction only. Its design is based on one p-n junction and two outputs. The rectifier diode changes the current from alternating to direct. In addition, rectifier diodes are widely used in electrical circuits for voltage multiplication, circuits where there are no strict requirements for signal parameters in terms of time and frequency.

Principle of operation
Basic device parameters
Rectifier circuits
Pulse devices
Imported devices

Principle of operation

The operating principle of this device is based on p-n features transition. Near the junctions of two semiconductors there is a layer in which there are no charge carriers. This is the barrier layer. His resistance is great.

When a layer is exposed to a certain external alternating voltage, its thickness becomes smaller and subsequently disappears altogether. The current that increases is called forward current. It runs from the anode to the cathode. If external AC voltage will have a different polarity, then the blocking layer will be larger, the resistance will increase.

Types of devices, their designation

By design, there are two types of devices: point and planar. In industry, the most common are silicon (designation - Si) and germanium (designation - Ge). The former have a higher operating temperature. The advantage of the latter is the low voltage drop with forward current.

The designation principle for diodes is an alphanumeric code:

The first element is the designation of the material from which it is made;
The second defines a subclass;
The third denotes work capabilities;
The fourth is the development serial number;
Fifth – designation of sorting according to parameters.

The current-voltage characteristic (volt-ampere characteristic) of a rectifying diode can be represented graphically. The graph shows that the current-voltage characteristic of the device is nonlinear.

In the starting quadrant Current-voltage characteristics its direct branch reflects the highest conductivity of the device when a direct potential difference is applied to it. The reverse branch (third quadrant) of the current-voltage characteristic reflects the situation of low conductivity. This occurs when the potential difference is reversed.

Actual current-voltage characteristics are dependent on temperature. As the temperature increases, the direct potential difference decreases.

From the graph of the current-voltage characteristic it follows that with low conductivity, current does not pass through the device. However, at a certain value of the reverse voltage, an avalanche breakdown occurs.

The current-voltage characteristic of silicon devices differs from germanium devices. Current-voltage characteristics are given depending on different temperatures environment. The reverse current of silicon devices is much less than that of germanium devices. From the graphs of the current-voltage characteristic it follows that it increases with increasing temperature.

The most important property is the sharp asymmetry of the current-voltage characteristic. With forward bias - high conductivity, with reverse bias - low. It is this property that is used in rectifying devices.

Analyzing the device characteristics, it should be noted: such quantities as the rectification coefficient, resistance, and capacitance of the device are taken into account. These are differential parameters.

The rectification factor reflects the quality of the rectifier.

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The rectification factor can be calculated. It will be equal to the ratio of the forward current of the device to the reverse. This calculation is acceptable for an ideal device. The value of the rectification coefficient can reach several hundred thousand. The larger it is, the better the straightener does its job.

Basic device parameters

What parameters characterize the devices? Main parameters of rectifier diodes:

The highest value of the average forward current;
The highest permissible reverse voltage value;
The maximum permissible frequency of the potential difference at a given forward current.

Based maximum value direct current, rectifier diodes are divided into:

Low power devices. They have a forward current value of up to 300 mA;
Medium power rectifier diodes. The forward current range is from 300 mA to 10 A;
Power (high power). Value more than 10 A.

There are power devices that depend on the shape, material, and type of installation. The most common ones are:

Medium power power devices. Their technical specifications allow you to work with voltages up to 1.3 kiloVolt;
Power, high power, capable of passing current up to 400 A. These are high-voltage devices. There are different housings for power diodes. The most common are pin and tablet types.

Rectifier circuits

The circuits for connecting power devices are different. To rectify the mains voltage, they are divided into single-phase and multiphase, half-wave and full-wave. Most of them are single phase. Below is the design of such a half-wave rectifier and two voltage graphs on a timing diagram.

Alternating voltage U1 is supplied to the input (Fig. a). On the right side of the graph it is represented by a sine wave. The diode state is open. Current flows through the load Rн. During the negative half-cycle the diode is closed. Therefore, only a positive potential difference is supplied to the load. In Fig. its time dependence is reflected. This potential difference operates during one half-cycle. This is where the name of the scheme comes from.

The simplest full-wave circuit consists of two half-wave circuits. For this rectification design, two diodes and one resistor are sufficient.

Diodes transmit only positive wave alternating current. The disadvantage of the design is that during the half-cycle the alternating potential difference is removed only from half of the secondary winding of the transformer.

If in the design instead of two diodes we use four coefficients useful action will rise.

Rectifiers are widely used in various industries. A three-phase device is used in automobile generators. And the use of the invented alternating current generator contributed to reducing the size of this device. In addition, its reliability has increased.

In high-voltage devices, high-voltage poles, which are composed of diodes, are widely used. They are connected in series.

Pulse devices

A pulsed device is a device whose transition time from one state to another is short. They are used to work in pulse circuits. Such devices differ from their rectifier analogues in small capacitances p-n transitions.

For devices of this class, in addition to the parameters indicated above, the following should be included:

Maximum pulse forward (reverse) voltages, currents;
Direct voltage installation period;
Recovery period of the device's reverse resistance.

Schottky diodes are widely used in high-speed pulse circuits.

Imported devices

The domestic industry produces a sufficient number of devices. However, today imported ones are most in demand. They are considered to be of higher quality.

Imported devices are widely used in television and radio circuits. They are also used to protect various devices when connected incorrectly (wrong polarity). The number of types of imported diodes is varied. There is no full-fledged alternative replacement for them with domestic ones yet.

A rectifier diode is a diode based on a semiconductor material that is designed to convert alternating current into direct current. True, the scope of application of these radio components is not limited to this function: they are used for switching, in high-current circuits, where there is no strict regulation of the time and frequency parameters of the electrical signal.

Classification

In accordance with the value of the forward current, which is the maximum permissible, the rectifying diode can have low, medium and high power:

small - rectify direct current up to 300 mA;
medium power rectifier diodes - from 300 mA to 10 A;
large - more than 10 A.

Germanium or silicon

According to the materials used, they are silicon and germanium, but more wide application found silicon rectifier diodes due to their physical properties.

Their reverse currents are several times less than in germanium ones, while the voltage is the same. This makes it possible to achieve very high permissible reverse voltages in semiconductors, which can be up to 1000-1500 V. In germanium diodes this parameter is in the range of 100-400 V.

Silicon diodes are able to remain operational in the temperature range from -60 ºС to +150 ºС, and germanium diodes - only from -60 ºС to +85 ºС. This happens because when the temperature rises above 85 ºС, the number of electron-hole pairs formed reaches such values that the reverse current sharply increases and the rectifier stops working effectively.

Manufacturing technology

The design of a rectifying diode is a wafer of a semiconductor crystal, in the body of which there are two regions with different conductivities. This is the reason why they are called planar.

Semiconductor rectifier diodes are made like this: in the region of the semiconductor crystal with n-type conductivity, aluminum, indium or boron is melted, and in the region of the crystal with p-type conductivity, phosphorus is melted.

When exposed high temperatures these two substances are firmly fused to the semiconductor base. In addition, the atoms of these materials diffuse into the crystal to form a region with predominantly electronic or hole conductivity. As a result, a semiconductor device is formed that has two regions with different types of electrical conductivity, and a p-n junction is formed between them. This is the operating principle of the vast majority of planar diodes made of silicon and germanium.

Design

In order to organize protection from external influences, as well as to achieve reliable heat dissipation, a crystal having a p-n junction is mounted in a housing.
Diodes with low power are produced in a plastic housing, equipped with flexible external leads. Medium power rectifier diodes have a glass-metal housing with rigid external leads. High-power parts are housed in a metal-glass or metal-ceramic housing.

Silicon or germanium crystals with a pn junction are soldered to a crystal holder, which also serves as the base of the housing. A body with a glass insulator is welded to it, through which the output of one of the electrodes goes.

Low power diodes, which have relatively small dimensions and weight, have flexible leads, through which they are mounted in circuits.

Since the currents with which medium-power semiconductors and high-power rectifier diodes operate reach significant values, their terminals are much more powerful. Their lower part is made in the form of a massive base that removes heat, equipped with a screw and a flat outer surface, which is designed to ensure reliable thermal contact with the external radiator.

Characteristics

Each type of semiconductor has its own operating and limiting parameters, which are selected in order to ensure operation in any circuit.

Parameters of rectifier diodes:

I straight max- direct current, which is the maximum permissible, A.
U return max - reverse voltage, which is the maximum permissible, B.
I return- reverse current constant, µA.
U straight- direct voltage constant, V.
Operating frequency, kHz.
Operating temperature, WITH.
P max- power dissipated by the diode, which is the maximum permissible.

The characteristics of rectifier diodes are far from exhausted by this list. However, they are usually sufficient to select a part.

Circuit of the simplest AC rectifier

Let's look at how the circuit works (the rectifier diode plays a role in it main role) primitive rectifier.

AC mains voltage with positive and negative half-cycles is supplied to its input. A load (R load) is connected to the output of the rectifier, and the function of the element rectifying the current is performed by a diode (VD).

Positive half-cycles of voltage applied to the anode cause the diode to open. At this time, direct current (I direct) flows through it, and therefore through the load (R load), which is powered by the rectifier.

Negative half-cycles of voltage applied to the anode of the diode cause it to close. A small reverse diode current flows through the circuit (I reverse). Here the diode cuts off the negative half-wave of the alternating current.

As a result, it turns out that a pulsating, rather than an alternating current of one direction, now passes through the load connected to the network (R load), through the diode (VD). After all, it can take place exclusively in positive half-cycles. This is the meaning of AC rectification.

However, such a voltage can only power a low-power load that is powered from an AC mains and does not have serious power requirements, for example, an incandescent lamp.

The lamp will transmit voltage only when positive pulses pass through, as a result of which the electrical appliance is subject to slight flickering with a frequency of 50 Hz. True, due to the fact that the thread is subject to thermal inertia, it will not be able to completely cool down in the intervals between pulses, which means that the flickering will be almost unnoticeable.

If such voltage is applied to an amplifier or power receiver, a low frequency sound (50 Hz) will be heard in the loudspeaker, which is called AC hum. This effect occurs because the pulsating current, when passing through the load, induces a pulsating voltage in it, generating a hum.

This disadvantage is to some extent eliminated if a filter capacitor (C filter), the capacitance of which is quite large, is connected in parallel with the load.

The capacitor will be charged by current pulses during positive half-cycles, and discharged through the load (R load) during negative half-cycles. If the capacitor capacity is sufficient, during the time that passes between two current pulses, it will not have time to completely discharge, and therefore, there will be a constant current on the load (R load).

But even with such a relatively smooth current, the load should not be powered either, because it will continue to generate noise, because the magnitude of the ripples (U puls.) is still quite serious.

Flaws

The rectifier we just discussed uses only half of the alternating current waves to its advantage, resulting in a loss of more than half of the input voltage. This type of AC rectification is called half-wave, and rectifiers that use this type of rectification are called half-wave. The disadvantages of half-wave rectifiers have been successfully eliminated in rectifiers using a diode bridge.

Diode bridge

A diode bridge is a compact circuit that is made up of four diodes and serves the purpose of converting alternating current to direct current. The bridge circuit makes it possible to pass current in each half-cycle, which distinguishes it favorably from the half-wave circuit. Diode bridges are produced in the form of small-sized assemblies, which are enclosed in a plastic housing.

At the output of the housing of such an assembly there are four pins marked “+”, “ — " or " ~ ", indicating the purpose of the contacts. However, diode bridges are also found not in an assembly; they are often assembled directly on a printed circuit board by connecting four diodes. The rectifier, which is performed on a diode bridge, is called full-wave.

There are many instruments and devices that convert electrical current. We propose to consider what high- and medium-power rectifier diodes are, their operating principle, as well as characteristics and applications.

Description of rectifier diodes

A high and medium power rectifier electrical diode (microwave) is a device that allows electric current move in one direction only, it is mainly used to operate a specific power source. Rectifier diodes can handle higher current than conventional conductors. As a rule, they are used to convert alternating current into direct current, the frequency of which does not exceed 20 kHz. The scheme of their work is as follows:

Photo - Operating principle of a rectifying diode

Many electrical devices require these discrete components because they can act as integrated circuits. Most often, power rectifier diodes are made of silicon, due to which their PN junction surface is quite large. This approach provides excellent current transfer, while ensuring the absence of short circuits or surges.

Photo - Rectifier diodesRectifier diodes

Silicon semiconductor rectifiers and tube thermionic diodes are made using compounds such as copper or selenium oxide. With the introduction of semiconductor electronics, vacuum tube type rectifiers with a metal base became obsolete, but their analogues are still used in audio and television equipment. Nowadays, semiconductor diodes are mainly used to power devices from very low to very high current. various types(high-speed units, foreign germanium devices, domestic tablet devices, Schottky diodes, etc.).

Other devices that are equipped with control electrodes, where a simpler rectification method or variable output voltage is required (for example, for welding machines) use more powerful rectifiers. These can be silicon or germanium devices. These are thyristors, zener diodes, or other controlled commutation solid-state switches that function like diodes, allowing current to flow in only one direction. They are used in industrial electronics, and are also widely used for electrical engineering, welding or monitoring the operation of current transmission lines.

Photo - Rectifier diode and cathode with anode

Types of Standard Rectifiers

There are various power rectifier semiconductor diodes depending on the type of installation, material, shape, number of diodes, and level of current passed. The most common are:

Medium power devices that can transmit current from 1 to 6 Amps. Moreover, the technical parameters of most devices say that such diodes can change the current from voltage to 1.3 kilovolts;
Rectifier diodes of the maximum series can pass current from 10 Amps to 400, they are mainly used as ultra-fast converters for controlling industrial activities. These devices are also called high-voltage;
Low frequency or low power diodes.

Before purchasing any devices of this type, it is very important to correctly select the basic parameters of rectifier diodes. These include: I-V characteristics (maximum reverse current, maximum peak current), maximum reverse voltage, forward voltage, case material and average rectified current.

We provide a table where you can, depending on your needs, select the type of diode. Specified specifications may change at the request of the manufacturer, so check the seller’s information before purchasing.

Photo - Table of low-frequency diodes

Imported (foreign) rectifier diodes (KVRS, SMD type):

Photo - Table of imported diodes

Data about power or high-frequency diodes:

Photo - Power diodes

Rectifier circuits are also different. They can be single-phase (for example, automotive and avalanche diodes) or multi-phase (three-phase is considered the most popular). Most low-power rectifiers for domestic equipment are single-phase, but three-phase is very important for industrial equipment. For generator, transformer, machine tools.

But at the same time, six diodes are used for an uncontrolled three-phase bridge rectifier. Therefore, it is often called a six-diode rectifier device. Bridges are considered pulsed and are capable of normalizing and rectifying even unstable current.

For low-power devices ( charger) double diodes connected in series with the anode of the first diode are also connected to the cathode of the second, and are manufactured in a single housing. Some commercially available dual diodes have all four terminals available, which can be configured to suit your needs.

Photo - Medium power rectifier diode

For higher power, one discrete device typically uses each of the six bridge diodes. It can be used both for surface equipment and for monitoring more complex devices. Often six-diode bridges use limiting circuits.

Video: The principle of operation of diodes