Solid state optoelectronic relays. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Electrician

Solid state optoelectronic relays. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Electrician's Handbook

solid state relay is called an optoelectronic device in which the control signal is transmitted through an optical channel and turns on / off a powerful output electronic device.

Applications of Solid State Relays

Currently, relays are increasingly used in various electrical devices and automation products, in particular:

for switching electric motors of direct and alternating current;
in automatic regulation and control systems;
as contactors in AC circuits, in switching power supplies, in high-speed protection systems, etc.

General classification of solid state relays

Optoelectronic solid state relays can be divided into two fundamentally different groups:

AC relays, in which the power elements are triacs and thyristors and unipolar;
bipolar DC relays with power elements on IGBT or MOSFETs, and bipolar relays can also work in AC circuits.

Let's compare in terms of efficiency (minimization of power dissipated in power elements) the use of thyristor and bipolar relays on IGBTs or MOS transistors in AC circuits. For typical values of the parameters of power elements for voltages of 220/380 V, we find that at currents above a few amperes, thyristors are 3-5 times more efficient than IGBTs, and the ratio of dissipated powers of the relay on IGBTs or MOS transistors is numerically approximately equal to the current in amperes.

AC solid state relays, classification

There are the following main types of thyristor solid state relays:

single-phase normally closed and normally open relays (from 1 A to 100 A);
three-phase normally open relays (from 10 A to 150 A);
single-phase, two-phase and three-phase reversing relays with built-in protection against phase-to-phase short circuit and instantaneous reverse (from 10 A to 40 A);
two-channel solid state relays with separate channels or with a common point at the output with independent channel control (from 1 A above).

Methods of management

Relays may have power voltage phase zero control (i.e. turn on when the value of this voltage is close to zero, such as TM) Or don't have that control (type TC). Turning on at "zero" voltage has the advantage of minimizing turn-on noise.

According to the control, the relays can have current or potential inputs. Moreover, only single-phase and two-channel relays can have current inputs, potential - for all. For current inputs, the control current is 10-25 mA with an input voltage drop of about 1,2 V or 2,4 V.

Potential control ranges:

constant (4-7) V and (3-30) V;
variable (6-30) V and (110-280) V.

Organization of protection of solid state relays

Thyristor structures are very sensitive to overvoltages - their appearance leads to irreversible breakdown, so the task of protecting relay outputs from overvoltages is an urgent task. The main means of such protection is shunting the relay outputs with varistors. To protect the relay from loss of control due to impulse noise, shunting of the outputs with an RC circuit is used.

DC Solid State Relays, Classification

DC Solid State Relays can also be classified by relay on/off delays.

High-speed relays have on/off delays of a few microseconds, an additional external power output and, in turn, are divided into such groups:

relay with power galvanically connected to the output and with power at the input;
relays with turn-off delays are significantly shorter (up to 1 ms).

Note that the so-called multi-channel relays are also produced with various combinations of "normally closed" and "normally open" contacts, in particular two- and four-channel ones.

Author: Koryakin-Chernyak S.L.

See other articles Section Electrician's Handbook.

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