Author Ren Jie
Solid state relay acts as an electronic switch that is turned off without mechanical contact components, more reliable, the switching speed, no noise and creping, plus control current, can be compatible with the general CMOS circuitry. Therefore, in the development of daily electronics and electronic products, multi-solid relay replaces ordinary electromagnetic relays. Solid state relays are typically composed of an input constant current control portion, a photocoupler isolation portion, and an output power switch portion. Of course, when the known input voltage varied, we can omit the constant current portion. Different types of photocouplers and power switching elements can be used when the load power supply is exchanged or DC in practical applications. When the power supply is DC, the photocoupler can select a 4N series (light-receiving device as a photosensitive triode), the power switching element crystal triode or the Dalinton composite tube; the power supply is exchanged, the photocoupler can choose the MOC306X series (light receiving) The device can view the two-way trigger diode of the optical control), and the power switching element is a one-way thyristor or a bidirectional thyristor.
working principle
Figure 1 is a schematic diagram of an AC solid state relay. The constant current circuit is constituted by R1, R2, VT1, and VT2 to ensure that the photocoupler operates in a wide range of fluctuations. When the control terminal adds a voltage, the current flows through R1 to turn the VT2, and the VT1 is also turned on, and the VT1 emission electrode is kept about 0.6V, that is, the voltage of R2 is about 0.6V, so flowing over R2 The current is 0.6 / R2, and the current flowing through the photocoupler is also 0.6 / R2, which is substantially different from the change in the control voltage. It is measured, and when R1 = 47Ω, the control voltage is changed between 3 to 30 V, the collector current of VT2 is maintained at around 11 mA, and the amount of change is not more than ± 1mA. The photocoupler realizes the signal transmission of light as a medium, so that the input / output end is reliably isolated, and the isolation belt withstand voltage is 1 kV or more. The power switch selects a bidirectional thyristor, R3 is a trigger current resistor, R4 and C series to absorb the high voltage in an instant.
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Component selection
The constant current selection is selected according to the parameters in the figure, and there is no special requirements. The photocoupler in Fig. 1 is selected for 4 N25 and MOC3063, and the like. Both optical coupling use double-column-in-six-pin packages, and the shape is shown in Figure 2, and the bid is marked with the pin arrangement corresponding to the internal structure. The selection of the power triode or thyristor determines the load capacity of the solid state relay. When T is selected with BT136 and BCR3AM in Fig. 1, the load current is up to 3A; when the BCR10AM is selected, the maximum current is 10A. If the load current is less than 1a, T can be used with a small tube such as Mac97a6, which will greatly reduce the volume of the finished product. If the load current is large, it is necessary to add a certain size of the radiator to VT4 and T when necessary. When the load power supply is 220V, the voltage of C is not less than 400V. The author uses the control of the pressure-resistant 1kV for the electric power supply.
Production steps
The entire circuit is very simple, and it can be made on a small porous plate. When making it, pay attention to the input and output terminals as far as possible, especially when the load power is used as AC 220V. The author is as shown in the table, and the size is 30mm (length) × 18 mm (width) × 20 mm (high). Leave 4 pins in the input / output. For convenience of distinguishing, the input terminal uses a finer lead, and the positive electrode is left longer; the output terminal uses a thicker lead, and the two are long, see Figure 3. There is no need for any indication, you can arrange the pin according to the lead. After the welding is correct, it can be sealed with a hot melt glue, or is loaded with an appropriate insulating housing with a size. Making solid state relays can replace electromagnetic relays in the circuit. This solid-state relay is lowered below 3V, and the upper limit voltage is higher than 30 V, so it is very versatility. In this journal, 10 light-emitting diodes were replaced with such a solid state relay to control 10 sets of white colors (of course, at this time, it should be omitted) Have a good effect.
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