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What are the selection criteria for solid state relays?
When selecting solid state relays for small current specification printed circuit boards, because the lead terminals are made of high thermal conductivity materials, welding should be stopped under the conditions of temperature less than 250 ℃ and time less than 10S. If you think about the reason for the surrounding temperature, you can think about derating application if necessary, and generally control the load current within 1/3 of the rated value. When the charged load is turned on, a large surge current will be generated. Because the heat is too late to distribute, it is likely to damage the SCR inside the SSR. Therefore, the user should analyze the surge characteristics of the charged load when selecting the relay, and then select the relay. The relay can accept this surge current under the premise of ensuring steady-state operation. When selecting, refer to Table 2 for derating coefficients of various loads (at normal temperature).
If the selected relay needs to work in places with frequent work, high service life and high reliability requirements, it should be multiplied by 0.6 on the basis of Table 2 to ensure reliable work. Ordinary in the selection in accordance with the above principles, when the low voltage request signal distortion is small, can choose to use FET as the output device of the DC solid state relay; For example, for AC resistive loads and most rational loads, zero-crossing relays can be selected, which can prolong the service life of loads and relays and reduce their own radio frequency interference. As the phase output control (PWM signal), should be selected random type solid state relay, the market is acquiesced in the zero type solid state relay.
The load of the solid-state relay can be greatly affected by the ambient temperature and its own temperature rise. During the operation of the device, it should be ensured that it has good heat dissipation conditions. Products with rated working current above 10A should be equipped with radiators, and products above 40A should be equipped with radiators and fans. When the device should pay attention to the bottom of the relay and the good contact with the radiator, and think about the appropriate amount of heat conduction silicone grease to achieve the best heat dissipation effect. For example, when the relay works at high temperature for a long time (40 ℃ ~ 80 ℃), the user can think about the derating application to ensure normal operation according to the maximum output current and ambient temperature curve data provided by the manufacturer.
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