The solid state relay is a new type of non-contact switch composed of solid state electronic components. It utilizes the switching characteristics of electronic components (such as switching transistors, semiconductor components such as triacs) to achieve contactless, spark-free, and turn-on and The purpose of breaking the circuit, it is also known as "non-contact switch." However, it is widely used in computer peripheral interface devices, constant temperature systems, signals, instrumentation equipment, automatic washing machines, and so on. What are the solid-state relay models? When you use them, how do you choose? Let's take a look with me.
What is a solid state relay
The solid state relay, abbreviated as SSR, is a non-contact switching device that consists entirely of solid-state electronic components. Compared with electromechanical relays, solid state relays have no mechanical movement and no moving parts, but their function is the same as that of electromechanical relays. Solid state relays mainly consist of input circuits, output circuits, and isolation.
Solid state relay structure
Solid state relays consist of three parts: input circuits, isolation (coupling) and output circuits.
Input circuit
According to different types of input voltage, the input circuit can be divided into three types: DC input circuit, AC input circuit and AC-DC input circuit. Some input control circuits also have TTL/CMOS compatible, positive and negative logic control and inverting functions, which can be easily connected with TTL and MOS logic circuits.
For a control signal with a fixed control voltage, a resistive input circuit is used. The control current is guaranteed to be greater than 5mA. For a large range of control signals (eg, 3~32V), a constant current circuit is used to ensure that the current is reliable at more than 5mA over the entire voltage range.
Isolated coupling
There are two kinds of isolation and coupling methods for the input and output circuits of solid state relays: optoelectronic coupling and transformer coupling: Photoelectric coupling usually uses photodiodes—phototransistors, photodiodes—bidirectional light-controlled thyristors, photovoltaic cells, and the control and load sides are implemented. Isolation control; high-frequency transformer coupling is the use of the input control signal generated by the self-excited high-frequency signal coupled to the secondary, after detection and rectification, logic circuit processing to form the drive signal.
Output circuit
The power switch of the SSR is directly connected to the power supply and the load end, and the on-off switching of the load power supply is realized. High-power transistors (Transistor), thyristors (Thyristor or SCR), Triacs, MOSFETs, insulated gate bipolar transistors (IGBTs) are mainly used. . The output circuit of the solid state relay can also be divided into a DC output circuit, an AC output circuit, and an AC-DC output circuit. According to the type of load, it can be divided into DC solid state relays and AC solid state relays. Bipolar devices or power FETs can be used for DC output, and usually two SCRs or one bidirectional SCR are used for AC output. AC solid state relays can be divided into single-phase AC solid state relays and three-phase AC solid state relays. AC solid-state relays, according to the timing of turn-on and turn-off, can be divided into random AC solid state relays and zero-cross AC solid state relays.
Solid state relay use
Dedicated solid state relays can have short-circuit protection, overload protection and over-temperature protection functions, and the combined logic curing package can realize the intelligent modules required by the user and can be directly used in the control system.
Solid state relays have been widely used in computer peripherals interface equipment, constant temperature systems, temperature control, electric furnace heating control, motor control, CNC machinery, remote control systems, industrial automation devices; signal lights, dimming, scintillation devices, lighting stage lighting control systems; instruments Instruments, medical equipments, copiers, automatic washing machines; automatic fire protection, security systems, and power switches that are used as power factor compensation for power grids, etc., as well as extensive use in explosion-proof, moisture-proof, and corrosion-resistant occasions such as chemical and coal mines. .
Solid State Relay Advantages
(1) High lifespan and high reliability: Solid state relays have no mechanical parts, and the solid parts complete the contact function. Since there are no moving parts, they can work under high shock and vibration conditions due to the components that make up the solid state relay. The inherent characteristics of the solid state relay determine the long life and high reliability.
(2) High sensitivity, low control power, and good electromagnetic compatibility: The solid-state relay has a wide input voltage range, low driving power, and is compatible with most logic ICs without the need for buffers or drivers.
(3) Fast conversion: Since the solid state relay uses a solid device, the switching speed can be from a few milliseconds to several microseconds.
(4) Small electromagnetic interference: Solid state relays do not input “coils†and there are no contact arcs and rebounds, which reduces electromagnetic interference. Most AC output solid-state relays are zero-voltage switches that conduct at zero voltage and shut off at zero current, reducing the sudden interruption of the current waveform, thereby reducing switching transients.
Solid State Relay Disadvantages
(1) After the conduction, the pressure drop of the tube is large, the forward voltage drop of the SCR or bidirectional silicon control can reach 1~2V, the saturation voltage drop of the high power transistor is also between 1~2V, and the general power MOSFET The on-resistance is also greater than the contact resistance of the mechanical contacts.
(2) The semiconductor device can still have leakage currents of several microamperes to several milliamps after shutdown, and thus cannot achieve ideal electrical isolation.
(3) Because the pressure drop of the tube is large, the power consumption and heat generation after conduction are also large. The volume of the high-power solid state relay is much larger than that of the electromagnetic relay with the same capacity, and the cost is also high.
(4) The temperature characteristics of electronic components and the anti-interference ability of electronic circuits are poor, and the radiation resistance is also poor. If no effective measures are taken, the work reliability is low.
(5) Solid state relays are more sensitive to overload and must be overloaded with a fast fuse or RC damping circuit. The load of the solid state relay is obviously related to the ambient temperature. As the temperature increases, the load capacity will drop rapidly.
(6) The main drawback is that there is an on-state voltage drop (corresponding cooling measures), off-state leakage current, AC and DC cannot be used universally, the number of contact groups is small, and over-current, over-voltage and voltage increase rate, current rise rate, etc. Poor indicators.
Solid State Relay Model
Solid state relay models are very rich. General-purpose solid-state relays mainly include single-phase AC solid state relays, dual AC solid state relays, and three-phase AC solid state relays. Among them, single-phase AC solid state relays mainly include JGJ11, JGJ12, ​​JGJ13, JGJ14, JGJ15, JGJ16, and JGJ19; AC solid state relay models mainly include JGJ21 and JGJ22; and three-phase AC solid state relay models mainly consist of JGJ31, JGJ32, JGJ33, JGJ34, and JGJ35.
In addition, there are differences in the types of DC and rectifier solid state relays, among which the single-phase DC solid state relays mainly include JGZ01, JGZ03, JGZ02, JGZ05, JGZ08, and JGZ09; the single-phase rectifier solid state relays mainly include JGZ11, JGZ12, JGZ13, and JGZ14; Rectifier solid state relays JGZ31, JGZ32.
There are also some special solid-state relays, such as single-phase composite solid state relay models mainly JGT11, JGT12, JGT13; AC dual-phase solid state relay models mainly JGT14; DC dual-phase solid state relay models mainly JGT06; three-phase composite solid state Relay models mainly include JGT34, JGT35 and JGT36. Types of phase failure protection solid state relays mainly include JGT33; positive and negative switching solid state relay models mainly include JGT37 and JGT38; and three-phase solid state relay assembly models mainly include JGT39.
Editor's summary: In the selection of solid-state relays, users need to pay attention to the difference between the solid-state relay models of different manufacturers, as long as they can choose according to their actual situation. For more information, please continue to pay attention to our website, follow-up will show more exciting content.
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