Solid state relays can be divided into AC type AC-SSR and two types of DC (DC-SSR) by load type. They are used to be used on an AC or DC power supply, which cannot be mixed. Chang Hui instrument only introduces commonly used AC solid state relays. The AC Solid State Relays and Principle As shown in Figure 1, it can be seen from the figure that it is a four-terminal active device, with two input control terminals, two output controlled ends. It has both an enlarged drive effect and there is an isolated role. It uses an electrical isolator to electrically isolate an input and output. In the input, a DC or pulse signal is added, the output can be converted from the shutdown state into a turning state (blocking when there is no signal), thereby controlling a larger load.
Solid state relay classification
The AC solid relay is divided into voltage cross zero guidelines (referred to as zero-shaped) and random conductive type (referred to as random type) by switching mode; with two-way controllable output type (ordinary) and one-way Controllable silicon reflatable (enhanced); needle-in-printed circuit board with printed wiring board (natural cooling, no needle with radiator) and device formula to a metal bottom plate (cooling); In addition, the input ends have a wide range input (DC3-32V) constant current source and string resistance limit streaming.
1 difference between zero-type and random solid state relays
When the input is applied to an effective control signal, the random-type solid state relay output is turned on (speed is micro-second), while the zero-type solid state relay will wait until the load voltage is zero zero area (about ± 15V) . When the input ends withdraw the control signal, all zero-type and random solid state relays are turned off when the current is maintained. Although cross-zero solid state relay may cause a half cycle delay, it reduces the impact of the load and the generated radio frequency interference, which is an ideal switching device, and is widely used in the "single-knife single throw" switching occasion. The random-type solid state relay is characterized by fast response speed, which can control the phase truncation pulse to facilitate changing the AC grid voltage, thereby applied to the modulation, dimming and other resistive loads and partial sensitive load applications.
2 The common type of two-way thyristor output and unidirectional controllable silicon against the enhanced difference
In the case of inductive load, when the SSR is turned off, due to the current, the phase is inconsistency, a large voltage rise rate DV / DT (commutation DV / DT) is added to the two-way controllable silicon. Such a value exceeds the two-way thyristor DV / DT indicator (typically 10V / μs) will result in delaying and even fail. The one-way thyristor is a single polarity operating state, only affected by the static voltage rise rate DV / DT (typical value of 100V / μs), and the enhanced SSR ratio consisting of two one-way controllable silicon is contracted by one The commutational SSR of the two-way controllable constituent is greatly improved, so the enhanced SSR is preferably selected in an inductive or capacitive load.
Solid state relay use occasion
Solid relays are currently widely used in computer peripheral interface devices, electric furnace heating constant temperature systems, CNC machinery, remote control systems, industrial automation devices, signal lights, scintillators, lighting stage lighting control systems; instrumentation, medical equipment, copiers, automatic washing machines; The fire, security system, and power capacitance of the power supply factor compensated for the power network, etc.
Solid state relay advantages and disadvantages
Solid relay work reliably, long life, noise, no spark, no electromagnetic interference, fast switching speed, strong anti-interference ability, small size, impact resistance, oscillation, explosion-proof, moisture, anti-corrosion, can be used with TTL, DTL, Logic circuits such as HTL are compatible with a tiny control signal to directly drive large current load. The main shortcomings are the existence of generic voltage drop (the corresponding heat dissipation measures), there is a broken-state leakage current, and the direct flow cannot be universal, the number of contacts is small, and the overcurrent, overvoltage and voltage increase rate, current increase rate and other indicators.
AC solid state relay basic performance test circuit
In general, the multimeter cannot discriminate the good and bad SSR, the correct method adopts the test circuit of Figure 2: When the input current is zero, the voltage measured by the voltage meter is the grid voltage, the light is not lit (the light bulb power must be 25W); When the input current reaches a certain value, the voltage is on, the voltage measured by the voltage is SSR conduction voltage drop (below 3V). (Please take care of the first user to note that there is a leakage current inside the SSR, so it cannot be equally equal to the general contact relay, contactor, please refer to the notes later).
Solid state relay selection
Solid state relay models have not been unified. When selecting, refer to the manual of the manufacturer, and should consider the following conditions when parameter selection.
1 rated input voltage
It refers to the effective value of the allowable voltage of the steady-state resistive load that can withstand under a given condition. When used for inductive load, the selected rated input voltage must be greater than twice the power supply voltage value, and the breakdown voltage of the selected product should be higher than twice the peak value of the load supply voltage. The AC load is a resistive load of 220V, optionally 220V voltage level SSR; an alternating load of 220V, an inductive load or a resistive load of 380V, optionally 380V voltage level SSR; AC load is 380V sensive load, The SSR of the 480V voltage level can be selected; the motor is inversion to the 480V voltage level SSR; frequently started single-phase or three-phase motor load, the SSR of the 660-800V voltage level can be selected.
2 rated output current and surge current
The rated output current refers to the current effective value that can be affected under a given condition (ambient temperature, rated voltage, power factor, having no heat radiator, etc.). Solid state relays have strong sensitivity to temperature, and after the operating temperature exceeds the marking value, it is necessary to use the amount or extension heat exchanger, and usually the manufacturers provide a hot degradation curve.
The surge current refers to the non-repetitive peak current that does not cause sexual damage under a given condition (ambient temperature, rated voltage, rated current, and continuous time, etc.). Resistance load, SSR can be used in full or decline 10%. Electric heater, the contactor is turned on the moment of surge current to reach three times the steady-state current, and the SSR should be used by 20% to 30%.
Solid state relay use and maintenance
Do not reverse the losers and outputs when the solid state relay is wiring. Pay attention to the following items.
1 The surge current affects the SSR in the SSR, there is a surge current, such as the electric heating element is a pure resistive load, has a positive temperature coefficient, the electrical resistance is small, and the current is large when the initial power is. If the heat inside the SSR is not emanded, the thyristor may be damaged, and there is a certain current margin when selecting the SSR. Using resistors, the current level of SSR should be greater than 2-22.5 times greater than the load rated current.
2 The use of ambient temperature affects the load capacity of the solid-state relay is larger, and there is a good heat dissipation condition in the use of the temperature, and the SSR of the rated operating current is above 10A, and the SSR above 100A should The ferroelectric heat saver is strong. Attention should be aware of the good contact of the SSR bottom and the heat sink at the time of installation, and heat-free silicone is applied. The SSR works in a 40-80 ° C state in a long time to use the amount of current rating.
3 overcurrent, overvoltage protection measures overcurrent and load short circuit can cause SSR damage, and should be protected by setting fast fuses and air switches in the control circuit, and can protect in parallel RC absorption loops and varistors in SSR output.
4 input loop signal
If the input voltage or input current exceeds the specified, the input signal can be partially divided or the input signal is subjected to the requirements of the input signal to match the SSR requirements. The input signal line should be kept away from the electromagnetic interference source to prevent actions.
Solid state relays are typically derived from a thermostat or a phase trigger. If you want to use a solid state relay, you should go to the thermostat or the phase trigger product page to learn more about these two solid relay supporting products and wiring. Knowledge!
Reprinted from Verid Electronic Market Network.
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