Solid state relay selection principle _ solid state relay selection elements

Solid-state relays with short-circuit protection, overload protection and overheating protection functions are widely used in electronic computer peripheral equipment, electric furnace heating control, constant temperature system and various anti-corrosion occasions. At the same time, due to its different application scope, shape and function differences, many friends in the purchase of solid state relay will worry about how to choose and type, the next to introduce the solid state relay in the selection of common matters needing attention.

 First, pay attention to the temperature and time factors of the use environment

For applications in small current specifications on printed circuit board, it is higher requirements for welding temperature, need in less than 250 degrees, and completed within 10 seconds, because the lead terminal for high thermal conductivity material, at the same time, if the user need to consider the surrounding temperature when using the solid state relay, then in the purchase relay to consider the size of the rating.

 Second, consider the characteristics of the load surge

I believe that everyone who knows the electronic components knows that when the components are connected, the moment will produce a surge current, and the surge is large, if the heat at this time, it is likely to cause damage to the silicon control inside the solid state relay. Therefore, the user should calculate and analyze the controlled load surge characteristics when selecting the relay, so that the relay can work stably and withstand the surge current.

 Third, take into account the factors of the installation environment

 Given the load capacity of solid state relay itself is vulnerable to the ambient temperature and its temperature rise, people in the purchase relay must consider the cooling condition of the installation environment, when necessary to match the corresponding fan cooling, so, when the installation environment temperature is not stable should choose the heat dissipation better relay components.

1, according to the load attributes to choose AC solid state or DC solid state, DC control DC (DC-DC) or DC controlled AC (DC-AC), generally we commonly use is DC controlled AC, can be bought on the market. DC control DC is not commonly used, except online and some large markets, it is difficult to buy.

2. Select the single-phase or three-phase solid-state relay according to the load mode to be controlled.

3, according to the type of load to select different specifications of the model of perceptual load, capacitive load or resistance load, to determine the voltage parameters, current parameters, etc.

4, generally we choose the relay should be more than one third of the load, if the control motor motor is recommended 5-7 times, if it is the DC motor or perceptual load is recommended more than 6 times, to prevent the reverse electric momentum too high breakdown of the solid state relay.

5, solid state relay generally need to be fixed on the heat sink, so when the load is large (generally 10 AY above to increase heat dissipation) in the relay at the same time must select the corresponding heat sink.

6, solid state relay in the resistance load caused by short circuit breakdown generally need to be equipped with RC circuit or varistor, to protect the solid relay.

7, in the solid state relay of printed circuit board, because the lead terminal is made of high thermal conductivity material, welding should be in the temperature of less than 250℃, time less than 10S, if considering the cause of the surrounding temperature, reduction can be considered when necessary, generally the load current control within 1 / 2 of the rated value.

8. Selection of solid-state relay SSR by various load surge characteristics

 The charged load will produce a large surge current at the moment of connection. Because the heat is too late to emit, it is likely to damage the internal SSR. Therefore, the user should analyze the surge characteristics of the charged load when selecting the relay, and then select the relay. So that the relay can withstand the surge current under the premise of ensuring steady state operation, refer to the 2 ating coefficient of various loads (at room temperature).

 If the selected relay needs to work in frequent operation, life and reliability requirements, multiply it by 0.6 based on Table 2 to ensure reliable operation.

 Generally, the above principles are followed. In the low voltage requirement, for the AC resistance load and most sensitive load, the over-zero relay can be selected, which can extend the load and relay life, and also reduce its own RF interference. If used as the phase output control, the random solid-state relay should be selected.

1. Solid state relay according to the switching load performance, can be divided into two categories of dc and ac type, ac has "zero" and "more than zero" two types of products, the switch contact have often open type and often closed type two, often open type is a more on the market, in the circuit design and the choose and buy, be sure to make clear the design requirements and accused of load.

2. The AC SSR is designed for working at 50 HZ. In the application, the frequency of the controlled AC power supply is required to work normally in the range of 40-60 HZ, and the waveform should be a sine wave. In this frequency range, whether the goods can work normally under the action of not pure sine wave depends on the specific situation of the product.

3. When selecting a specific solid state relay, first determine its electrical performance parameters, such as input voltage or current, output voltage or current, overload current and dv / dt, etc., whether the actual required technical indicators match or match, and whether the external circuit or load match, etc.

4. When choosing a certain model, we need to consider its shape, assembly mode and heat dissipation.

5. The load capacity of the solid state relay is related to the temperature of the working environment. When the ambient temperature increases, the load capacity of the solid state relay decreases, so there should be sufficient room in selecting the rated working current of SSR.

6. When the solid state relay is on, the power dissipation will make the shell temperature height, and the maximum load current decreases with the increase of the shell temperature. In order to make the solid state relay full operation, it should reduce its own heat generation and strengthen the heat dissipation effect, and appropriate specifications of heat dissipation plate can be installed.

7. When connecting the solid-state relay, pay attention to the size and polarity of the dc control voltage.

8. For ac solid state relay, the output and RC absorption loop is necessary, during the purchase, should make clear model whether configured RC absorption circuit, may some installed, some not installed, for perceptual load, especially heavy sensitive load, in addition to the RC absorption circuit, but also should increase the pressure stor. The nominal operating voltage of the varistors is 1.9 times the effective value of the optional supply voltage.

9. Welding time problem, when using the pinhole welding SSR and trigger is SSR, the gas welding temperature should not be higher than 260℃, welding time is less than 10S, for screw fixed SSR, the washer should be added to prevent loosening, and the torque should not be too large, to prevent damage during the period.

10. The isolation mode between input and output of solid state relays include photoelectric isolation and dry clarinet relay isolation. Using photoelectric isolation mode, the reverse breakdown voltage of the light emitting diode is only about 6V. In order to ensure the safety of the device, a protective diode should be connected in series in the light emitting Russian-Japanese mechanism circuit to prevent reverse breakdown.

11. Pay attention to the specified working current. When the voltage of the input signal source is high, the serial current limiting resistance must be connected in the input circuit.

12. When using, must pay attention to the load connected to the output end of the solid state relay must not short circuit.