Modern life is unthinkable without television. In many apartments you can find two and sometimes three television receivers. Cable TV is especially popular. But what if you need to connect several TVs to one antenna cable? It is natural to use a “Chinese” double or even tee.
For example, like this one:
I installed just such a double splitter on two TVs to receive cable TV channels. However, the quality of reception left much to be desired; if the channels of the first meter range were shown tolerably, then the channels of the second and UHF ranges were received with strong signal attenuation. Having disassembled the splitter, I found in it a small double ferrite ring and several turns of single-core wire:
The device is a high-frequency transformer with antiphase winding. And in theory, it should exclude the mutual influence of the input circuits for receiving the RF signal, but in fact it only weakened it, apparently due to the fact that there was a galvanic connection
I decided to replace the transformer with ordinary ceramic capacitors (red flags) with a nominal value of several picofarads, thereby eliminating this galvanic connection:
My surprise knew no bounds; both TVs were shown as if only one was working, i.e. not the slightest hint of mutual influence and excellent reception on all bands.
The containers fit into the splitter housing:
The only thing I blame myself for is why this idea didn’t come to me earlier.
International Rectifier, a designer and manufacturer of power electronics since 1947, produces a huge range of opto-relays for all kinds of applications. The most popular of them can be divided into the following groups:
- Fast acting (PVA, PVD, PVR);
- General purpose (PVT);
- Low voltage medium power (PVG, PVN);
- High voltage powerful (PVX).
PVA33: fast acting relay
for signal switching
AC Relay Series PVA33— single pole, normally open. Designed for general analog signal switching purposes.
The operating principle of the device is as follows (Fig. 1). The voltage applied to the relay input causes current to flow through the gallium arsenide LED (GaAlAs), resulting in an intense glow of the latter. The light flux hits an integrated photovoltaic generator (IGG), which creates a potential difference between the gate and the source of the output switch, thereby transferring the latter to a conducting state. Power MOSFET transistors (HEXFET - patented IR technology) are used as power output switches. In this way, complete galvanic isolation of the input circuits from the output circuits is achieved.
Rice. 1.
The advantages of such a solution compared to conventional electromechanical and reed relays are a significant increase in service life and speed, reduction in power losses, and minimization of size. These benefits improve the quality of products developed for a variety of applications, such as signal multiplexing, automated test equipment, data acquisition systems, and others.
The voltage level that the relays of this series are capable of switching lies in the range from 0 to 300 V (amplitude value) of both alternating and direct current. In this case, the minimum level is determined (at constant current) by the resistance of the channel of the output transistors, which averages about 1 Ohm (maximum up to 20 Ohms).
The dynamic characteristics of the device are determined by the on-off time, which is about 100 μs. Thus, the guaranteed relay switching frequency can reach 500 Hz or more.
The maximum frequency of the switched signal depends mainly on the frequency characteristics of the transistors used and for MOS switches reaches hundreds of kilohertz. The relays are supplied in 8-pin DIP packages and are available in two versions: through-hole and surface mount.
PVT312: telecommunication relay
general purpose
Photoelectric relay PVT312, single-pole, normally open, can be used on both direct and alternating current.
This solid state relay is specially designed for use in telecommunication systems. Relay series PVT312L(suffixed with "L") use active current limiting circuitry, which allows them to withstand transient current surges. PVT312 is available in a 6-pin DIP package.
Applications: telecommunications keys, triggers, general switching circuits.
Connection diagrams can be of three types (Fig. 2). In the first case, two chip keys are connected in series. Due to the symmetry, this allows the resulting circuit to switch alternating voltage. This type of circuit is called a type “A” connection. Type “B” differs in that only one of the two chip keys is used. This allows you to switch a larger, but only direct current. In the third option (type “C”), the keys are connected in parallel, thereby increasing the maximum possible current value.
Rice. 2.
PVG612: low voltage medium voltage relay
power for AC
Photoelectric Relay Series PVG612 - unipolar, normally open solid state relays. The compact devices of the PVG612 series are used for isolated switching of currents up to 1 A with voltages from 12 to 48 V AC or DC.
Relays of this type are interesting in that they are capable of switching relatively large (for this type of device) alternating currents, while maintaining the operating speed inherent in solutions based on MOS transistors.
PVDZ172N: low voltage medium
power for DC
Relays of this series (Fig. 3), unlike those described above, are designed for switching currents only of constant polarity with a power of up to 1.5 A and a voltage of up to 60 V. For example, these relays are used in controlling lighting devices, motors, heating elements, etc. .d.
Rice. 3.
PVDZ172N Available in normally open, single-pole design in 8-pin DIP packages.
Other possible applications: audio equipment, power supplies, computers and peripherals.
PVX6012: for heavy loads
For large low frequency loads, IR offers photoelectric relay PVX6012(Fig. 4) (single-pole, normally open). The device uses an output switch based on an insulated gate bipolar transistor (IGBT), which makes it possible to obtain a low voltage drop in the on state and low loss currents in the closed state at a fairly high operating speed (7 ms on / 1 ms off).
Rice. 4.
The PVX6012 is available in a 14-pin DIP package, which, interestingly, uses only four pins - this solution allows for better cooling of the device.
Main applications include: test equipment; industrial control and automation; replacement of electromechanical relays; replacement of mercury relays.
PVI: photo insulator for external
high power keys
Devices in this series are not relays in the proper sense of the word. That is, they are not able to commute large energy flows with the help of small ones. They only provide galvanic isolation of the input from the output, hence their name - photoelectric insulator (Fig. 5).
Rice. 5.
Why is such a “underreliance” necessary? The fact is that the PVI series devices produce, upon receiving an input signal, an electrically isolated DC voltage, which is sufficient to directly control the gates of high-power MOSFETs and IGBTs. In fact, this is an opto-relay, but without an output switch, for which the developer can use a separate transistor suitable for its power.
PVIs are ideal for applications requiring high current and/or high voltage switching with optical isolation between control circuitry and high power load circuits.
In addition, the series insulator PVI1050N contains two simultaneously controlled outputs, which makes it possible to connect them in series or in parallel to provide a higher control current (MOC) or a higher control voltage (IGT). Thus, in fact, you can get an output signal of 10 V/5 μA when connected in series and 5 V/10 μA when connected in parallel.
The two outputs of the PVI1050N can be used separately, provided that the potential difference between the outputs does not exceed 1200 VDC. The input-output isolation is 2500 VDC.
Devices of this series are produced in 8-pin DIP packages and are used in organizing the control of powerful loads, voltage converters, etc.
PVR13: double fast acting relay
The main feature of this series is the presence of two independent relays in one housing (Fig. 6), each of which can be connected as type “A”, “B”, or “C” (for an explanation of the types, see above in the description of PVT312). Maximum switching voltage 100 V (DC/AC), current 300 mA. Otherwise, this relay is close in scope and characteristics to the PVA33 and is also intended for switching analog signals of medium frequency (up to hundreds of kilohertz).
Rice. 6.
Available in 16-pin DIP packages with pins for through-hole mounting.
The main characteristics of IR optoelectronic relays are presented in Table 1.
Table 1. Parameters of IR optoelectronic relays
| Characteristics | PVA33 | PVT312 | PVG612N | PVDZ172N | PVX6012 |
|---|---|---|---|---|---|
| Input characteristics | |||||
| Minimum control current, mA | 1…2 | 2 | 10 | 10 | 5 |
| Max. control current for being in the closed state, mA | 0,01 | 0,4 | 0,4 | 0,4 | 0,4 |
| Control current range (current limitation required!), mA | 5…25 | 2…25 | 5…25 | 5…25 | 5…25 |
| Maximum reverse voltage, V | 6 | 6 | 6 | 6 | 6 |
| Output characteristics | |||||
| Operating voltage range, V | 0…300 | 0…250 | 0…60 | 0…60 (constant) | 280 (AC)/400 (DC) |
| Maximum continuous load current at 40°C, A | 0,15 | - | - | 1,5 | 1 |
| A conn. (post or variable) | - | 0,19 | 1 | - | - |
| In connection (fast.) | - | 0,21 | 1,5 | - | - |
| With connection (fast.) | - | 0,32 | 2 | - | - |
| Maximum pulse current, A | - | - | 2,4 | 4 | not a repeat. 5 A (1 sec) |
| Resistance in open state, no more, Ohm | 24 | - | - | 0,25 | - |
| A conn. | - | 10 | 0,5 | - | - |
| In connection | - | 5,5 | 0,25 | - | - |
| With connection | - | 3 | 0,15 | - | - |
| Resistance in closed state, not less, MOhm | 10000 | - | 100 | 100 | - |
| Turn-on time, no more. ms | 0,1 | 3 | 2 | 2 | 7 |
| Shutdown time, no more, ms | 0,11 | 0,5 | 0,5 | 0,5 | 1 |
| Output capacitance, no more, pF | 6 | 50 | 130 | 150 | 50 |
| Voltage rise rate, not less, V/µs | 1000 | - | - | - | - |
| Other | |||||
| Electric strength of insulation “input-output”, V (SCR) | 4000 | 4000 | 4000 | 4000 | 3750 |
| Insulation resistance, input-output, 90 V DC, ohms | 1012 | 1012 | 1012 | 1012 | 1012 |
| Input-output capacitance, pF | 1 | 1 | 1 | 1 | 1 |
| Maximum contact soldering temperature, °C | 260 | 260 | 260 | 260 | 260 |
| Operating temperature, °C | -40…85 | -40…85 | -40…85 | -40…85 | -40…85 |
| Storage temperature, °C | -40…100 | -40…100 | -40…100 |
-40…100 | -40…100 |
Application of Optoelectronic Relays IR
Control systems. In ACS interfaces, one of the pressing problems is the organization of communication between the control and switched circuits, ensuring reliable galvanic isolation. That is, it is necessary to organize the transmission of information (for example, a signal to an actuator) without electrical contact. One of the first devices of this kind were electromechanical relays, in which information was transmitted via a magnetic field. However, the presence of mechanical parts led to sparking contacts and low performance of such systems.
The use of signal transmission through a light flux (optoelectronic relays) in automated control system interfaces (Fig. 7) compared to electromechanical switches provides higher reliability, switching speed, durability, and better weight and size indicators; and the advantage in comparison with electronic switches is the absence of a common point and mutual influence of circuits during switching.
Rice. 7.
The presence of galvanic isolation in the control system is one of the important properties of the switch, because allows you to create separate control flows, which, in turn, makes it possible to ensure electrical independence of the information and executive zones of the system. Optical galvanic isolation isolates microelectronic control equipment from high-current and high-voltage circuits of peripheral execution devices, which leads to increased noise immunity, service life and reduced price of such equipment.
Rice. 8.
Another necessary function in measuring equipment is switching operating modes (measuring range, gain, type of connection, etc.), which was previously performed mechanically. For example, to measure voltage, a voltmeter is connected to the circuit in parallel, while to measure current, the measuring equipment must be connected in series to the circuit. In some instruments, to implement such a switch, it was necessary to use another input, mechanically switching the measuring line. This is quite inconvenient if the measured parameter changes frequently, so the use of optoelectronic relays can effectively solve this problem, significantly increasing the ease of use of the device.
On the other hand, in data acquisition systems the need to use opto-relays is often due to the high probability of damage to the sensitive input circuits of the measuring equipment (analog-to-digital and frequency converters). Such an undesirable effect may arise, for example, due to the long length of the conductors from the primary transducer to the measuring element, which contributes to the induction of electrostatic interference. In addition, both transient processes during switching on/off of the equipment and errors in its use, for example, the presence of a large amplitude input signal during a power outage, can have a significant impact.
All these factors lead to the need to use galvanic isolation. An example is the PVT312L series relay with a built-in active ripple current suppression circuit, which can be effectively used in devices associated with long conductors or operating in difficult electromagnetic conditions (wired environmental monitoring systems of enterprises, industrial measuring transducers).
Telecommunications. The use of opto-relays in the field of communications is also a promising area. There are several unique functions that can be effectively implemented using the advantages of an opto relay. This includes galvanic isolation between the modem and the telephone line to prevent damage associated with electrostatic (including lightning) discharges; implementation of specific functions of telephone equipment (pulse and tone dialing, connection and determination of line status), etc.
Conclusion
In recent years, there has been a trend towards a constant increase in demand for optoelectronic relays from IR. The main consumers of solid-state relays are the industrial giants of our country - instrument-making and transport enterprises, large state corporations Rostelecom, Rosatom, Russian Railways. Manufacturers value the convenience and high technical performance of IR relays for industrial applications.
On the other hand, the requirements for the reliability of electronic equipment from the military and aerospace industries are constantly growing. The issue is very relevant, which requires specific technical solutions that will reduce equipment failures during operation. None of the experts doubt that solid-state relays can increase the reliability of special-purpose equipment.
The series of articles consists of three parts:
Interference in circuits.
During normal operation of an electronic device, interference may occur in the circuit.
Interference can not only interfere with the normal operation of the device, but also lead to its complete failure.
Rice. 1. Interference in the useful signal.
You can see the interference on the oscilloscope screen by including it in the part of the circuit under study (Fig. 1). The duration of interference can be either very short (a few nanoseconds, so-called “needles”) or very long (several seconds). The shape and polarity of the interference also varies.
The propagation (passage) of interference occurs not only along the wire connections of the circuit, but sometimes even between parts of the circuit that are not connected by wires. In addition, interference can overlap and add up to each other. Thus, a single weak interference may not cause a malfunction in the device circuit, but the simultaneous accumulation of several weak random interferences leads to incorrect operation of the device. This fact makes the search and elimination of interference many times more difficult, since it takes on an even more random nature.
Sources of interference can be roughly divided:
- External source of interference. A strong electromagnetic or electrostatic field source near the device may cause the electronic device to malfunction. For example, a lightning discharge, relay switching of high currents or electric welding.
- Internal source of interference. For example, when you turn on/off a reactive load (an electric motor or an electromagnet) in a device, the rest of the circuit may malfunction. An incorrect program algorithm can also be a source of internal interference.
To protect against external interference, the structure or its individual parts are placed in a metal or electromagnetic shield, and circuit solutions with less sensitivity to external interference are also used. The use of filters, optimization of the operating algorithm, changes in the construction of the entire circuit and the location of its parts relative to each other help against internal interference.
What is considered very elegant is not the indiscriminate suppression of all interference, but the deliberate direction of them to those places in the circuit where they will fade out without causing harm. In some cases, this path is much simpler, more compact and cheaper.
Assessing the probability of interference in circuits and ways to prevent them is not a simple task, requiring theoretical knowledge and practical experience. But nevertheless, we can firmly say that the probability of interference increases:
- with an increase in switched current or voltage in the circuit,
- with increasing sensitivity of parts of the circuit,
- with an increase in the performance of the used parts.
In order not to redo the finished design due to frequent failures, it is better to become familiar with the possible sources and paths of interference at the circuit design stage. Since about half of all manifestations of interference are associated with “bad” power supply, it is best to start designing a device by choosing a method for powering its parts.
Interference in power supply circuits.
Figure 2 shows a typical block diagram of an electronic device, which consists of a power source, control circuit, driver and actuator.
Most of the simplest robots from the series on this site are built according to this scheme.
Rice. 2. Joint power supply of the control and power parts.
In such circuits we can conditionally distinguish two parts: control and power. The control part consumes relatively little current and contains any control or computing circuits. The power section consumes significantly more current and includes an amplifier and termination load.
Let's look at each part of the circuit in more detail.
Rice. 2 a.
Power supply(Fig. 2 a.) can be “batteries” or a mains transformer power supply. The power supply may also include a voltage stabilizer and a small filter.
Rice. 2 b.
Control circuit- this is part of the circuit (Fig. 2 b.), where any information is processed in accordance with the operation of the algorithm. Signals from external sources, for example, from some sensors, can also come here. The control circuit itself can be assembled using microcontrollers or other microcircuits, or using discrete elements.
Communication lines they simply connect the control circuit to the driver-executive device, that is, these are just wiring or tracks on a printed circuit board.
Rice. 2nd century
Actuator(Fig. 2 c.) is often a mechanism that converts an electrical signal into mechanical work, such as an electric motor or electromagnet. That is, the actuator converts electrical current into another form of energy and usually consumes a relatively large current.
Rice. 2 years
Since the signal from the control circuit is very weak, so driver or amplifier(Fig. 2 d) is an integral part of many schemes. The driver can be made, for example, using only a transistor or a special chip, depending on the type of actuator.
As a rule, the main source of strong interference is the actuator. The interference that appears here, having passed through the driver, spreads further along the power bus (The interference in Fig. 2 is shown schematically by an orange arrow). And since the control circuit is powered from the same power source, there is a high probability that this interference will affect it as well. That is, for example, an interference that appears in the motor will pass through the driver and can lead to a failure in the control circuit.
In simple circuits, it is enough to place a large capacitor of about 1000 μF and a ceramic 0.1 μF capacitor in parallel with the power source. They will act as a simple filter. In circuits with consumption currents of about 1 ampere or more, to protect against strong interference of complex shapes, you will have to install a bulky, complex filter, but this does not always help.
In many circuits, the easiest way to get rid of the effects of interference is to use separate power supplies for the control and power parts of the circuit, that is, the use of the so-called separate power supply.
Although separate power supply is used not only to combat interference.
Separate meals.
In Fig. Figure 3 shows a block diagram of a certain device. This circuit uses two power supplies. The power part of the circuit is powered from power supply 1, and the control circuit is from power supply 2. Both power sources are connected by one of the poles; this wire is common to the entire circuit and signals are transmitted relative to it along the communication line.
Rice. 3. Separate power supply for the control and power parts.
At first glance, such a circuit with two power supplies looks cumbersome and complex. In fact, such separate power supply circuits are used, for example, in 95% of all household equipment. Separate power supplies there are just different windings of transformers with different voltages and currents. This is another advantage of separate power supply circuits: several units with different supply voltages can be used in one device. For example, use 5 volts for the controller, and 10-15 volts for the motor.
If you look closely at the diagram in Fig. 3, it can be seen that interference from the power part does not have the opportunity to get into the control part via the power line. Consequently, the need to suppress or filter it completely disappears.
Rice. 4. Separate power supply with stabilizer.
In mobile structures, for example, mobile robots, due to their size, it is not always convenient to use two battery packs. Therefore, separate power supply can be built using one battery pack. The control circuit will be powered from the main power source through a stabilizer with a low-power filter, Fig. 4. In this circuit, you need to take into account the voltage drop across the stabilizer of the selected type. Typically a battery pack with a higher voltage than the voltage required for the control circuit is used. In this case, the functionality of the circuit is maintained even when the batteries are partially discharged.
Rice. 5. L293 with separate power supply.
Many driver chips are specifically designed for use in circuits with separate power supply. For example, the well-known L293 driver chip ( Rice. 5) has a conclusion Vss- for powering the control circuit (Logic Supply Voltage) and output Vs- to power the final stages of the power driver (Supply Voltage or Output Supply Voltage).
In all robot designs with a microcontroller or a logic chip from the series, L293 can be switched on with a separate power supply circuit. In this case, the power supply voltage (voltage for the motors) can be in the range from 4.5 to 36 volts, and the voltage on Vss can be supplied the same as to power the microcontroller or logic chip (usually 5 volts).
If the power supply to the control part (microcontroller or logic chip) occurs through a stabilizer, and the power supply to the power part is taken directly from the battery pack, then this can significantly save energy losses. Since the stabilizer will only power the control circuit, and not the entire structure. This - Another advantage of separate power supply: energy saving.
If you look again at the diagram in Figure 3, you will notice that in addition to the common wire (GND), the power section is also connected to the control circuit by communication lines. In some cases, these wires can also carry interference from the power part into the control circuit. In addition, these communication lines are often highly susceptible to electromagnetic influences (“noise”). You can get rid of these harmful phenomena once and for all by using the so-called galvanic isolation.
Although galvanic isolation is also used not only to combat interference.
Galvanic isolation.
At first glance, this definition may seem incredible!
How can a signal be transmitted without electrical contact?
In fact, there are even two ways that allow this.
Rice. 6.
Optical signal transmission method based on the phenomenon of photosensitivity of semiconductors. For this, a pair of an LED and a photosensitive device (phototransistor, photodiode) is used, Fig. 6.
Rice. 7.
The LED-photodetector pair is located in isolation in one housing opposite each other. This is what this detail is called. optocoupler(foreign name optocopler), Fig. 7.
If current is passed through the optocoupler LED, the resistance of the built-in photodetector will change. This is how contactless signal transmission occurs, since the LED is completely isolated from the photodetector.
Each signal transmission line requires a separate optocoupler. The frequency of the optically transmitted signal can range from zero to several tens to hundreds of kilohertz.
Rice. 8.
Inductive signal transmission method is based on the phenomenon of electromagnetic induction in a transformer. When the current changes in one of the windings of the transformer, the current in its other winding changes. Thus, the signal is transmitted from the first winding to the second (Fig. 8). This connection between the windings is also called transformer, and a transformer for galvanic isolation is sometimes called isolation transformer.
Rice. 9.
Structurally, transformers are usually made on a ring ferrite core, and the windings contain several tens of turns of wire (Fig. 9). Despite the apparent complexity of such a transformer, you can make it yourself in a few minutes. Ready-made small-sized transformers for galvanic isolation are also sold.
Each signal transmission line requires a separate such transformer. The frequency of the transmitted signal can range from several tens of hertz to hundreds of thousands of megahertz.
Depending on the type of signal being transmitted and the circuit requirements, you can choose either transformer or optical galvanic isolation. In circuits with galvanic isolation, special converters are often installed on both sides to coordinate (connect, interface) with the rest of the circuit.
Let us now consider the block diagram using galvanic isolation between the control and power parts in Figure 10.
Rice. 10. Separate power supply and galvanic isolation of the communication channel.
From this diagram it can be seen that any interference from the power part has no way of penetrating into the control part, since there is no electrical contact between the parts of the circuit.
The absence of electrical contact between parts of the circuit in the case of galvanic isolation allows you to safely control actuators with high voltage power. For example, a control panel powered by a few volts can be galvanically isolated from a phase network voltage of several hundred volts, which increases safety for operating personnel. This is an important advantage of galvanic isolation circuits.
Control circuits with galvanic isolation can almost always be found in critical devices, as well as in pulsed power supplies. Especially where there is even the slightest chance of interference. But even in amateur devices, galvanic isolation is used. Since a slight complication of the circuit by galvanic isolation brings complete confidence in the uninterrupted operation of the device.
Galvanic isolation. Optocoupler circuit
| An optocoupler, also known as an optocoupler, is an electronic component that transmits electrical signals between two isolated electrical circuits using infrared light. As an insulator, an optocoupler can prevent high voltage from passing through a circuit. The transmission of signals through the light barrier occurs using an IR LED and a photosensitive element, for example a phototransistor, which is the basis of the optocoupler structure. Optocouplers are available in a variety of models and internal configurations. One of the most common is an IR diode and a phototransistor together in a 4-pin package, shown in the figure.
Certain parameters must not be exceeded during operation. These maximum values are used in conjunction with the graphs to correctly design the operating mode.
On the input side, the infrared emitting diode has a certain maximum forward current and voltage, exceeding which will cause the emitting element to burn out. But even a signal that is too small will not be able to make it glow, and will not allow the impulse to be transmitted further along the circuit. Advantages of optocouplers
Disadvantages of optocouplers
Application of optocouplers
The versatility of optocouplers as elements of galvanic isolation and contactless control, the diversity and uniqueness of many other functions are the reason that the scope of optocoupler applications has become computer technology, automation, communications and radio equipment, automated control systems, measuring equipment, control and regulation systems, medical electronics, devices for visual display of information. Read more about the different types of optocouplers in this document. |
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Galvanic isolation: principles and diagram
Galvanic isolation is the principle of electrical insulation of the current circuit in question in relation to other circuits that are present in one device and improves technical performance. Galvanic insulation is used to solve the following problems:
- Achieving signal chain independence. It is used when connecting various instruments and devices, ensuring the independence of the electrical signal circuit with respect to the currents arising during the connection of different types of devices. Independent galvanic coupling solves problems of electromagnetic compatibility, reduces the influence of interference, improves the signal-to-noise ratio in signal circuits, and increases the actual accuracy of measuring ongoing processes. Galvanic isolation with isolated input and output contributes to the compatibility of the devices with various devices under complex electromagnetic environment parameters. Multichannel measuring instruments have group or channel isolation. The isolation can be single for several measurement channels or channel-by-channel for each channel independently.
- Compliance with the requirements of the current GOST 52319-2005 on electrical safety. The standard regulates insulation resistance in electrical control and measurement equipment. Galvanic isolation is considered as one of a set of measures to ensure electrical safety; it must work in parallel with other methods of protection (grounding, voltage and current limiting circuits, safety valves, etc.).
Isolation can be provided by various methods and technical means: galvanic baths, inductive transformers, digital isolators, electromechanical relays.
Galvanic isolation solution diagrams
During the construction of complex systems for digital processing of incoming signals associated with operation in industrial conditions, galvanic isolation must solve the following problems:
- Protect computer circuits from exposure to critical currents and voltages. This is important if operating conditions involve exposure to industrial electromagnetic waves, there are difficulties with grounding, etc. Such situations also occur in transport, which has a large human influence factor. Errors can cause complete failure of expensive equipment.
- Protect users from electric shock. The problem is most often relevant for medical devices.
- Minimizing the harmful effects of various interferences. An important factor in laboratories performing precise measurements, when building precision systems, and at metrological stations.
Currently, transformer and optoelectronic isolation are widely used.
Operating principle of the optocoupler
Optocoupler circuit
The light-emitting diode is forward biased and receives only light from the phototransistor. This method provides a galvanic connection between circuits that are connected on one side to an LED and on the other side to a phototransistor. The advantages of optoelectronic devices include the ability to transmit communications over a wide range, the ability to transmit pure signals at high frequencies, and small linear dimensions.
Electrical impulse multipliers
They provide the required level of electrical insulation and consist of transmitter-emitters, communication lines and receiving devices.
Pulse multipliers
The communication line must provide the required level of signal isolation; in the receiving devices, the pulses are amplified to the values necessary to start the thyristors into operation.
The use of electrical transformers for isolation increases the reliability of installed systems built on the basis of serial multicomplex channels in the event of failure of one of them.
Parameters of multi-complex channels
Channel messages consist of information, command or response signals; one of the addresses is free and is used to perform system tasks. The use of transformers increases the reliability of the functioning of systems assembled on the basis of serial multicomplex channels and ensures the operation of the device when several recipients fail. Due to the use of multi-stage transmission control at the signal level, high levels of noise immunity are ensured. In the general operating mode, it is possible to send messages to several consumers, which facilitates the initial initialization of the system.
The simplest electrical device is an electromagnetic relay. But galvanic isolation based on this device has high inertia, is relatively large in size and can only provide a small number of consumers with a large amount of energy consumed. Such disadvantages prevent the widespread use of relays.
Galvanic isolation of the push-pull type allows you to significantly reduce the amount of electrical energy used in full load mode, thereby improving the economic performance of the devices.
Push-pull isolation
Through the use of galvanic isolations, it is possible to create modern automatic control, diagnostic and monitoring circuits with high safety, reliability and stability of operation.
plast-product.ru
Galvanic isolation. If not an optocoupler, who?
There is such a thing in electronics as galvanic isolation. Its classic definition is the transfer of energy or signal between electrical circuits without electrical contact. If you are a beginner, then this formulation will seem very general and even mysterious. If you have engineering experience or just remember physics well, then most likely you have already thought about transformers and optocouplers.
The article below the cut is devoted to various methods of galvanic isolation of digital signals. We’ll tell you why it’s needed at all and how manufacturers implement an insulation barrier “inside” modern microcircuits.
As already mentioned, we will talk about isolating digital signals. Further in the text, by galvanic isolation we will understand the transmission of an information signal between two independent electrical circuits.
Why is it needed?
There are three main tasks that are solved by decoupling a digital signal.
The first thing that comes to mind is protection against high voltages. Indeed, ensuring galvanic isolation is a safety requirement for most electrical appliances. Let the microcontroller, which naturally has a small supply voltage, set control signals for a power transistor or other high voltage device. This is a more than common task. If there is no insulation between the driver, which increases the control signal in power and voltage, and the control device, then the microcontroller risks simply burning out. In addition, input-output devices are usually connected to control circuits, which means that a person pressing the “turn on” button can easily close the circuit and receive a shock of several hundred volts. So, galvanic isolation of the signal serves to protect people and equipment. 
No less popular is the use of microcircuits with an insulation barrier to interface electrical circuits with different supply voltages. Everything is simple here: there is no “electrical connection” between the circuits, so the signal, the logical levels of the information signal at the input and output of the microcircuit, will correspond to the power supply on the “input” and “output” circuits, respectively. 
Galvanic isolation is also used to improve the noise immunity of systems. One of the main sources of interference in electronic equipment is the so-called common wire, often the device housing. When transmitting information without galvanic isolation, the common wire provides the common potential of the transmitter and receiver necessary for transmitting the information signal. Since the common wire usually serves as one of the power poles, connecting various electronic devices to it, especially power ones, leads to short-term impulse noise. They are eliminated by replacing the "electrical connection" with a connection through an insulating barrier. 
How it works
Traditionally, galvanic isolation is based on two elements - transformers and optocouplers. If we omit the details, the first ones are used for analog signals, and the second ones are used for digital signals. We are considering only the second case, so it makes sense to remind the reader who an optocoupler is. To transmit a signal without electrical contact, a pair of a light emitter (most often an LED) and a photodetector is used. The electrical signal at the input is converted into “light pulses”, passes through the light-transmitting layer, is received by a photodetector and is converted back into an electrical signal.
Optocoupler isolation has earned enormous popularity and has been the only technology for isolating digital signals for several decades. However, with the development of the semiconductor industry, with the integration of everything, microcircuits appeared that implement an insulation barrier using other, more modern technologies. Digital isolators are microcircuits that provide one or more isolated channels, each of which outperforms the optocoupler in terms of speed and accuracy of signal transmission, level of resistance to interference and, most often, cost per channel.
The isolation barrier of digital isolators is manufactured using various technologies. The well-known company Analog Devices uses a pulse transformer as a barrier in ADUM digital isolators. Inside the microcircuit housing there are two crystals and a pulse transformer, made separately on a polyamide film. The transmitter crystal generates two short pulses at the edge of the information signal, and one pulse at the decline of the information signal. A pulse transformer allows, with a slight delay, to receive pulses on the transmitter crystal through which the inverse conversion is performed.
The described technology is successfully used in the implementation of galvanic isolation; it is in many ways superior to optocouplers, but has a number of disadvantages associated with the sensitivity of the transformer to interference and the risk of distortion when working with short input pulses.
A much higher level of noise immunity is provided in microcircuits where the isolation barrier is implemented on capacitors. The use of capacitors eliminates DC coupling between the receiver and transmitter, which in signal circuits is equivalent to galvanic isolation. 
If the last sentence agitated you... If you felt a burning desire to scream that there cannot be galvanic isolation on capacitors, then I recommend visiting threads like this one. Once your rage has subsided, note that all of this controversy dates back to 2006. As we know, we will not return there, just like in 2007. And insulators with a capacitive barrier have been produced for a long time, used and work perfectly.
The advantages of capacitive decoupling are high energy efficiency, small dimensions and resistance to external magnetic fields. This makes it possible to create inexpensive integral insulators with high reliability indicators. They are produced by two companies - Texas Instruments and Silicon Labs. These companies use different technologies for creating the channel, but in both cases silicon dioxide is used as the dielectric. This material has high electrical strength and has been used in the production of microcircuits for several decades. As a result, SiO2 is easily integrated into the crystal, and a dielectric layer several micrometers thick is sufficient to provide an insulation voltage of several kilovolts. On one (at Texas Instruments) or on both (at Silicon Labs) crystals, which are located in the digital isolator housing, capacitor pads are located. The chips are connected through these pads, so the information signal passes from the receiver to the transmitter through the isolation barrier. Although Texas Instruments and Silicon Labs use very similar technologies for integrating a capacitive barrier on the chip, they use completely different principles for transmitting the information signal.
Each Texas Instruments isolated channel is a relatively complex circuit.
Let's look at its “lower half”. The information signal is supplied to RC circuits, from which short pulses are taken along the leading edge and falling edge of the input signal, and the signal is reconstructed from these pulses. This method of passing a capacitive barrier is not suitable for slowly changing (low frequency) signals. The manufacturer solves this problem by duplicating channels - the “lower half” of the circuit is a high-frequency channel and is intended for signals from 100 Kbps. Signals below 100 Kbps are processed in the "top half" of the circuit. The input signal is subjected to preliminary PWM modulation with a high clock frequency, the modulated signal is fed to the isolation barrier, the signal is restored using pulses from the RC circuits and is subsequently demodulated. The decision-making circuit at the output of the isolated channel “decides” from which “half” the signal should be sent to the output of the microcircuit.
As you can see in the Texas Instruments isolator channel diagram, both the low-frequency and high-frequency channels use differential signal transfer. Let me remind the reader of its essence.
Differential transmission is a simple and effective way to protect against common mode interference. The input signal on the transmitter side is “divided” into two signals V+ and V-, inverse to each other, which are equally affected by common-mode interference of different natures. The receiver subtracts the signals and, as a result, the Vsp interference is eliminated.
Differential transmission is also used in digital isolators from Silicon Labs. These microcircuits have a simpler and more reliable structure. To pass through the capacitive barrier, the input signal is subjected to high-frequency OOK (On-Off Keyring) modulation. In other words, a “one” of an information signal is encoded by the presence of a high-frequency signal, and a “zero” by the absence of a high-frequency signal. The modulated signal passes without distortion through a pair of capacitors and is restored at the transmitter side.
Judging by several recent posts, it would be nice to cover what galvanic isolation is and why it is needed. So:
Galvanic isolation- transfer of energy or signal between electrical circuits without electrical contact between them.
Now, let's look at some examples :)
Example 1: Network
Most often people talk about galvanic isolation in relation to mains power, and here's why. Imagine that you grabbed the wire from the socket with your hand. Your “connection” from an electrical point of view looks like this:And, yes, the leakage current of the slippers is quite enough for you to feel a “blow” when you touch the “phase” network wire. If the slippers are dry, then such a “blow” is usually harmless. But if you stand barefoot on a wet floor, the consequences can be very dire.
It’s a completely different matter if there is a transformer in the circuit: 
If you touch one of the terminals of the transformer, no current will flow through you - it simply has nowhere to flow, the second terminal of the transformer hangs in the air. If, of course, you grab both terminals of the transformer and it produces enough voltage, then it will screw you up anyway.
So, in this case, the transformer provides galvanic isolation. In addition to the transformer, there are a bunch of different ways to transmit a signal without creating electrical contact:
- Optical: optocouplers, fiber optics, solar panels
- Radio: receivers, transmitters
- Sound: speaker, microphone
- Capacitive: through a very small capacitor
- Mechanical: motor-generator
- You can still imagine
Example 2: Oscilloscope
There is a really mega-classic way to blow up half a circuit. There is even a corresponding one on the forum. The thing is, many people forget that the oscilloscope (and many other equipment) is connected to ground. Here's what the full picture looks like when connecting an oscilloscope to a circuit powered directly from the mains:
Remember - once you connect something to a circuit, it becomes part of the circuit! This is also true for various measuring equipment.
The correct way to measure something in a circuit like this is to connect it through a 220->220 isolation transformer: 
Ready-made transformers 220->220 are quite difficult to find. Therefore, you can use so-called shifters. A flip is two transformers, for example 220->24, turned off in series like this: 
You've probably seen what this looks like in practice: 
Inverters are even better than one 220->220 transformer.
- They provide half the capacitance between input and output
- The middle part can be grounded, and thus it is very good to filter out interference from the network
- You can turn on 3 transformers, and then you can get 440 or 110 volts
Song
A long time ago I even wrote a song on the topic of galvanic isolation. The song is under the spoiler.The song, its lyrics and explanations
I recorded this mini-song when I was working on various audio electronics. One friend made a tube guitar gadget and, thinking that the transformer that turns 220 into 220 was completely useless, threw it out of the circuit, for which he paid. I thought that this was quite the theme for a metal mini-song.
Hello Oldfag! Your browser does not support html5! Update yourself!
You didn't install an anode transformer
Powered directly from the network
There was a battery under my foot
And you grabbed the guitar with your handCurrent pierces the mortal body
Mortal flesh wriggles
You can't open your hand
You're alone and no one can helpTearing and burning
Electrons squeeze your heart
Will it fight or will it subside?
Safety, remember, comes first.
By the way, besides the denouement in this little song there are two more good pieces of advice:
- Yes, all work with mains voltage must be performed by at least two people.
- When an electric shock occurs, the hand contracts, so it is better to first touch the devices with the back of your right hand.
