1. The drive circuit directly affects the life of the LED
The LED driver we are talking about includes two types of digital driver and analog driver. Digital driver refers to digital circuit driver, including digital dimming control, RGB full-color change and so on. Analog drive refers to analog circuit drive, including AC constant current switching power supply, DC constant current control circuit. The drive circuit is composed of electronic components, including semiconductor components, resistors, capacitors, inductors, etc. These components have a service life, and the failure of any one device will lead to the failure of the entire circuit or partial function failure. The service life of the LED is 50,000 to 100,000 hours. Calculated according to 50,000 hours, it is continuously lit and has a service life of nearly 6 years. The life of switching power supply is difficult to reach 6 years. The quality guarantee period of switching power supply on the market is generally 2-3 years. Factory is hard to accept. Therefore, the faults of LED lamps are mostly drive circuit faults.
2. Heat dissipation problem
LED is a cold light source, the working junction temperature cannot exceed the limit, and a certain margin must be left in the design. The design of the whole lamp should consider many aspects such as beautiful appearance, convenient installation, light distribution, heat dissipation, etc. It is necessary to seek a balance point among many factors, so that the overall lamp is the best. The development of LED purification lamps is not long. There is not much experience for reference, and many designs are continuously improved. Some LED lighting manufacturers use outsourced or outsourced power supplies, and lighting designers don’t know much about power supplies, so there is a large space for heat dissipation of LEDs and less space for heat dissipation of power supplies. Generally, after designing the lamps and lanterns, find a suitable power supply to match, which brings certain difficulties to the matching of the power supply. It is often encountered that due to the small internal space of the lamp or the high internal temperature, and the low cost control, it is impossible to allocate a suitable power supply. Some LED lighting manufacturers have power supply research and development capabilities. The above problems can be solved by evaluating at the beginning of the design of lamps and synchronizing the design of power supply. In the design, it is necessary to comprehensively consider the heat dissipation of the LED and the heat dissipation of the power supply, and control the temperature rise of the lamps as a whole, so that a better lamp can be designed.
3. Problems in power supply design
a. Power design. Although the LED light efficiency is high, there is still 80-85% heat loss, resulting in a temperature rise of 20-30 degrees inside the lamp. If the room temperature is 25 degrees, the interior of the lamp is 45-55 degrees, and the power supply is in a high temperature environment for a long time. In order to ensure the service life, it is necessary to increase the power margin, generally leaving a margin of 1.5-2 times.
b. Component selection. When the internal temperature of the lamp is 45-55 degrees, the internal temperature rise of the power supply is still about 20 degrees, and the temperature near the components should reach 65-75 degrees. Some components will drift in parameters at high temperature, and some will have a shortened lifespan, so the device should be selected that can be used at a higher temperature for a long time, paying special attention to electrolytic capacitors and wires.
c. Electrical performance design. The switching power supply is designed for the parameters of the LED, mainly constant current parameters. The size of the current determines the brightness of the LED. If the batch current error is large, the brightness of the entire batch of lamps will be uneven. And temperature changes can also cause the power supply output current to shift. Generally, the batch error is controlled within +/-5% to ensure the brightness of the lamp is consistent. The forward voltage drop of the LED is biased, and the constant current voltage range of the power supply design should include the voltage range of the LED. When multiple LEDs are used in series, the minimum voltage drop multiplied by the number in series is the lower limit voltage, and the maximum voltage drop multiplied by the number in series is the upper limit voltage. The constant current voltage range of the power supply is slightly wider than this range. Generally, the upper and lower limits are different. Leave 1-2V margin.
d. PCB layout design. The size of the LED lamp left for the power supply is small (unless it is external to the power supply), so the PCB design has higher requirements and there are many factors to be considered. The safety distance should be enough, the power supply that requires input and output isolation, the primary side circuit and the secondary side circuit require a withstand voltage of 1500-2000VAC, and a distance of at least 3MM should be left on the PCB. If it is a lamp with a metal casing, the layout of the entire power supply should also consider the safety distance between the high-voltage part and the casing. If there is no space to ensure a safe distance, other measures should be used to ensure insulation, such as punching holes on the PCB, adding insulating paper, and potting insulating glue. In addition, the layout of the board should also consider the heat balance, and the heating elements should be evenly distributed and cannot be placed in a centralized manner to avoid local temperature rise. Electrolytic capacitors are kept away from heat sources, slow down aging and prolong service life.
e. Authentication issues. At present, there is no domestic standard for LED purification lamps. The relevant national departments are researching and formulating. The domestic sales of lamps and lanterns are certified according to the lighting standards. For export, they are certified by CE or UL. . Therefore, in view of this situation, it is difficult for the design of switching power supply to meet the above standards at the same time. We can only meet different certifications for different requirements.
4. Use parameters
The selection of outsourced power supply mainly depends on the constant current and constant current voltage range. The constant current value is selected to be lower than the standard current of the LED. The selection of the voltage range should be moderate, and try not to choose a large range to avoid waste of power.
The drive circuit affects the life of the LED, so the circuit design must be rigorous, the LED is a cold light source, and the junction temperature cannot exceed the limit. While maintaining the beautiful appearance, heat dissipation must be considered, and every step must be rigorous.
Benwei Lighting is an LED Tube, LED flood light, LED Panel Light, LED High Bay, LED manufacturer with 12 years of experience. If you want to purchase a high-quality LED flood light or have a more in-depth understanding of the application of LED flood lights, please contact send us inquiry， our web: https://www.benweilight.com/.
