Based on the light-emitting principle of LED and the characteristics of plant physiological activities, this study designs an LED plant growth light.After comparison, this design adopts a circular array combination, configures DD312 as the control chip of constant current source, and uses pulse width modulation technology to regulate the light to satisfy the light demand of different plants at different times, with a view to enhancing plant yield and shortening the In order to improve plant yield and shorten the growth cycle.
When using point light sources for light supplementation, traditional agriculture commonly uses electric light sources, together with the use of plastic film covering technology, to effectively regulate the cultivation environment and promote the growth and development of plants, but there are problems such as the light level is lower than the light compensation point and the light quality treatment is not pure. When encountering persistent cloudy and rainy weather, plants cannot carry out photosynthesis effectively. Therefore, it is necessary to design a new type of plant growth light. In this study, a set of LED plant growth lamps was designed to solve the problems of traditional electric light sources by combining the characteristics of plant growth.
LED Light-emitting Principle and Selection
1.1 LED light-emitting principle
LED is also known as light-emitting diode, is a new energy-saving devices, can effectively overcome the traditional light source short life, energy consumption, heat and other defects, is widely used in signal indication, lighting and backlighting technology, etc. The core light-emitting device of the LED is mainly divided into two parts, namely, the N-type semiconductor, P-type semiconductor wafers, and the area where the two are intersected is known as the PN junction. Current through the ends of the LED, the electron will be quickly pushed to the P area, at this time the PN junction will show a hole and electron composite state, and the release of energy, part of the energy in the form of light radiated to the outside, the rapid transformation into light energy. Simply put, the LED light-emitting principle is the process of mutual conversion of electrical energy and light energy.
1.2 LED light source selection
Combined with the market demand for LED plant growth lights, this design ultimately uses 1 W high-power blue, red and white combination of LED devices. blue and red LED light source wavelengths of 460 nm and 630 nm, respectively, which is consistent with the wavelengths needed for plant growth, indicating that the LED light source selected in this design can better meet the needs of plant photosynthesis.
1.3 LED array design
The matrix designed in this study adopts a circular array, which mainly consists of multiple LEDs and so on to form a circular light-emitting circle.
LED Plant Lighting Control System Design
2.1 Load connection method
This design mainly takes the load connection design scheme, so the series connection has higher advantages. In the traditional series connection circuit, if there is a short circuit or disconnection of LED holding, the LED lights can not operate normally. This design improves the series connection with a certain resistance at both ends of the LED.
2.2 LED driving circuit
2.2.1 Constant current driver circuit.
This kind of driving circuit can ensure that the current at both ends of the LED remains constant, ensuring that the LED emits light evenly and stably. Constant-current driver circuit to join the overload protection circuit, if the voltage on both sides of the LED suddenly rises, it can effectively avoid the LED in a short period of time because the current rises and burns. Therefore, many manufacturers like to use this LED drive. However, constant current drive circuit operation needs to be configured during the control source, the operation is more complex, the application cost is very high.
2.2.2 Resistor current limiting circuit.
This is one of the simplest LED drive circuit, mainly in the DC power supply LED circuit series connected to a resistor, by adjusting the resistance value to control the LED brightness. In this design, a high power (1 W) LED is used, so the actual value of V is 3.3 V, and the actual value of I is 350 mA. The resistor current limiting circuit is very simple and low cost, but at the same time, the disadvantages are very prominent. When the supply voltage changes, to ensure that the current passing through both sides of the LED remains the same, the current limiting resistor must be adjusted, which is difficult to achieve in practice.
2.2.3 Constant voltage drive.
Constant voltage drive is an important technology to maintain the voltage on both sides of the LED constant. At room temperature, the working current of the LED is about 20 mA, after the LED temperature rises to 85 ℃, its current will rise to 35 ~ 37 mA, but if the brightness of the LED does not appear to increase significantly, the increase in current will make the temperature of the PN node rise rapidly, prompting the LED service life to shorten rapidly, so it is usually not recommended to use this technology.
2.3 Pulse width modulation
Pulse Width Modulation (Pulse Width Modulation, PWM) technology has very prominent advantages, is very suitable for application in the control of LED lights, which is mainly through the control of the disconnection time and conduction, and effectively regulate the LED light intensity. When using PWM technology for square wave regulation, the brightness of the LED lights appear cumulative changes, but it usually has a large duty cycle, the human eye is often difficult to find the brightness of the light changes.
2.4 Driving LED circuit with DD312
This design uses the DD312 developed by Taiwan's SITI as the constant-current driver chip for the LED grow light. The main technical characteristics of the DD312 chip are as follows: the output current needs to reach 1 A, at this time the minimum output voltage is 1 V; the maximum output current is 1 A, and can be adjusted through the external resistor; the output of the maximum enabling frequency of 1 MHz; the output of the maximum withstand voltage of 18 V; with over-current protection, overheating alarm, monitoring the LED open-circuit function; the chip has a powerful function. The maximum working voltage of the chip is 5~18 V; the main form of package is SOP8 or TO-252. In constant current drive, this design adopts DD312 as the chip of the whole LED drive circuit, and reasonably uses PWM technology to effectively strengthen the control of the intensity of the red light and blue light.
For the power supply, the 5 V DC voltage is used to replace the previous 220 V AC voltage, at this time, the voltage of the LED light power module is set to 12 V. In addition, the microcontroller (STMicroelectronics, STM32 103 series) is used as the main control chip, which is low-cost, high-performance, low-power consumption, and it is the core chip of various embedded electronic products at present.
LED Plant Grow Light Design
The LED plant grow light designed in this paper mainly uses 3 groups of different circular LED arrays, each group consists of 9 LEDs, including 1 blue light with a wavelength of 460 nm (±30 nm), which is placed in the centre, and 8 red lights with a wavelength of 660 nm (±30 nm), which are placed in the periphery. There are 27 LEDs in the whole group, with a total power of 27 W.
In this design, the LED plant growth lamp needs to apply more LED lamps, during the work will inevitably produce a lot of heat, LED plant growth lamp temperature rises rapidly, which makes its luminous performance decline rapidly. Aluminium has a good heat dissipation function, at the same time, the density is small, so it will be used as a heat sink for the LED plant growth lamp, and configure temperature control equipment to strengthen the control of temperature changes, effectively ensure that the LED luminous performance.
In this design, the LED light source board can achieve the control of blue light and red light intensity through the serial port to meet the different light intensity requirements of different plants. After the LED plant growth lights designed in this study are put into use, the growth cycle of fruits and vegetables is significantly shortened, the yield is significantly increased, the sweetness of fruits and vegetables is increased, while the pest problem is effectively reduced.
At this stage, LED plant grow lights are important devices to enhance photosynthesis in indoor plants. After in-depth research, this paper designs a kind of LED plant grow light consisting of three groups of circular matrices with nine LEDs in each group. This kind of LED plant growth light can adjust the light intensity according to the temperature demand, with simple structure, easy operation and low application cost, which can better ensure the growth and development of plants, shorten the growth cycle and effectively improve the yield.