Solid state relay. Principle of operation. Connectivity

The most widely used solid-state relay found in the industry. Here it is used to create equipment that must be small in size and be reliable. The abbreviation in Cyrillic is TTR, and in Latin SSR. As the main minus of these devices is called the price. But within the framework of the article, we will only talk about the features and advantages that a solid-state relay has.

Principle of operation and construction

Let's first consider how a conventional relay is arranged. It is a device in which there are contacts and a control coil. In order for the device to work, we need a voltage that will be influenced. It will cause the contacts to open or close when it is fed to the coil. The solid-state relay works in a similar manner. Only here instead of contacts semiconductor devices are used. The most common are triacs, thyristors (to commute an alternating current) and transistors (for a constant). Also, solid-state relays use galvanic isolation between voltages on the power contacts and the coils. This is achieved due to the presence of an optocoupler at the input. If the functional is realized through thyristors and triacs, then it is said that before us are solid-state relays of alternating current.

Comparison

In general, each key transistor can be represented as a solid state relay. Let's recall how the majority of motion or light sensors are arranged. They are created in accordance with the principle that a transistor supplies the usual relay to a normal relay. Coil and semiconductor element as a contact. With regard to the use of triacs and thyristors, they can transmit current in both directions (which is not available to the transistor). If we continue our comparison further, it is worth noting that solid-state relays consume and lose much less energy during operation. They also have small dimensions, high speed, long service life and absolute noiselessness. But, despite all the advantages, we can not say that we can refuse conventional relays in the near future.

Intraspecific differences

There are solid-state relays:

1. The three-phase commutates the current in the range of 10 to 120 amperes immediately in 3 phases.
2. Reversible. Semiconductor devices that can conduct non-contact switching of DC and AC currents. In its main task coincide with single-phase relays. There must necessarily be a control circuit that provides protection against false activation. Reversible relays are characterized by three-phase operation and a long service life. This is possible due to the high-quality control and isolation mechanism, which is provided constructively for this type of device. When operating these devices there is no acoustic noise, bounce when switching and sparking.
3. Single-phase provides switching current when it passes through zero. Relay single-phase solid state operates in the range from 10 to 500 amperes. Management can be carried out in four ways.

Areas of use

Solid-state relays are used where it is necessary to adhere to the principle of having installed and forgotten about it. For comparison, consider an example. But before that, consider the extract from the instructions for normal contacts: even the manufacturer recommends cleaning them after several thousand cycles of closures.

But now for an example. At the enterprise there is a machine tool on which solenoid valves are installed . Power to them - 24VDC 2A. They are connected in parallel. Switched off / turned off approximately once per second. Power is supplied through the relay. Even if it can withstand and 10 amperes of inductive load, then change once a month, the second will have to. While a solid-state relay will allow you to forget about this for years. Although the planned technical inspection was not canceled. In this regard, it is desirable to focus on the recommendations received from the manufacturer in the accompanying documentation.

Indications for use

If normal contacts do not cope with their duties, burn like candles, then this is the best recommendation for use. Solid state relays can provide reliable operation. They easily cope with switching inductive loads. Also, if you need to make sure that the contacts do not stick, or there is a strict limitation in size - solid-state relays will come to your rescue.

What kinds of solid-state relays exist?

They are divided according to their device, as well as the principle of operation. For ease of understanding, I propose the following classification:

• Depending on the type of control voltage:

1. Constant (discrete).
2. The variable.

• Depends on the type of switched voltage:

1. Variable.
2. Constant.

• Depends on the number of phases of AC voltage:

1. Single.
2. Triple. There is still the possibility of dividing by the presence or absence of a reverse.

• According to the design features (where the installation is carried out):

1. On a surface.
2. On the DIN rail.

We choose a solid-state relay

It should be noted some features. Thus, conventional relays can easily withstand short-term overloads, the magnitude of which will be 150% or even 200% of the nominal value. If everything is done correctly, then the cleaning of contacts can be dispensed with in all cases. With a solid-state relay, this is not possible. So, if you exceed the indicator by 150%, you can safely throw the device. Therefore, for the active load, a reserve of 2-4 times must be provided for the rated current. If a solid-state relay is used to run asynchronous motors, this figure will need to be increased 6-10 times. Such a stock, although it forces you to choose more expensive parts, simultaneously allows you to guarantee a long life of the device to which the device is connected.

Add-ins for correct operation

When interacting with an inductive load, the structures can function with certain problems. Therefore, when working with transformers, electric bells, coils with magnetic circuits and similar devices, it is necessary to turn on the RC circuit in parallel to reduce the effect of anti-EMF. It will also reduce the overall inductance of the load, and the solid-state relay will be easier to operate.

Short circuit protection

Manufacturers for this case recommend the use of special fuses, which were developed for solid-state devices. Here is their classification:

1. GR - fuses operating with the whole range of operating currents. They are used to protect semiconductor elements. They are considered very fast.
2. GS - work with the whole range of operating currents. Used when the line experiences increased load, and also as protection of semiconductor elements.
3. AR - fuses that work with the whole range of operating currents. Used to protect semiconductor elements from short circuits.

It should be noted that the fuses are quite expensive. Therefore, as an alternative, protective devices (class B) are used.

Where can I get it?

Buy solid-state AC relays can be in the nearest radio electronics store. But this applies, as a rule, to those cases where the place of residence of the reader is a large city. In case this is not the case, you can advise to use the services of online stores. They, as a rule, are given delivery to the recipient for a certain amount or for free.

And what can we say directly about the value that a solid-state relay has? The price for these devices ranges from 600 rubles to several thousand.

Connection of solid-state relay

In this action there is nothing complicated. So, in order for the device to work, a control voltage must be applied to the input, observing the polarity. Let's talk about the features of this process:

1. It is desirable to carry out the connections in a screw manner, rather than by soldering.
2. To avoid damage to the device, it is necessary to check the absence of dust, as well as elements of metallic nature.
3. Try to do everything possible so that there are no unacceptable external influences on the body of the device (both during operation and in the off state).
4. Do not touch the relay during operation, to avoid getting burns. Also, make sure that the device is not located near flammable materials.
5. When connecting, make sure that the connections are properly switched.
6. If the device is heated by more than 60 degrees during its operation, it is necessary to obtain a cooling radiator for it.
7. Care should be taken to ensure that there is no short circuit at the output of the device. In the opposite case, it will simply fail.

Direct control of the solid-state relay can be carried out by means of a circuit in which various variants are provided. It is mounted on the plus-input.

Conclusion

We have considered a solid-state relay, the principle of operation, control, views, protection - everything that matters. Of course, this is not enough to independently install such a device in most cases.