2024-01-31
How to correctly choose LED driver power
How to correctly choose LED driver power
1, the drive circuit directly affects the LED life
The LED driver we say includes digital driver and analog driver two categories, digital driver exponential circuit driver, including digital dimming control, RGB full color change. Analog driver refers to the analog circuit driver, 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 part of the function. The service life of LED is 5-10 thousand hours, according to 50,000 hours, continuous lighting, has a life of nearly 6 years. The life of the switching power supply is difficult to reach 6 years, the warranty period of the switching power supply sold on the market is generally 2-3 years, and the power supply with a 6-year warranty is military-grade, and the price is 4-6 times that of the ordinary power supply, and the general lighting factory is difficult to accept. Therefore, the failure of LED lamps is mostly the driver circuit fault.
2. Heat dissipation problem
LED is a cold light source, the working junction temperature can not exceed the limit value, and a certain margin should be left in the design. The design of the whole lamp should consider beautiful appearance, easy installation, light distribution, heat dissipation and many other aspects of the problem, to seek a balance in many factors, so that the overall lamp is the best. The development time of LED lamps is not long, there is not much experience to learn from, and many designs are constantly improved. Some LED lighting manufacturers use power for outsourcing or outsourcing, lighting designers do not know much about the power supply, to the LED heat dissipation space is large, to the power dissipation space is small. Generally, it is to find the right power supply to match after the design of the lamp, which brings certain difficulties to the matching of the power supply. Often encountered because the internal space of the lamp is small or the internal temperature is high, and the cost control is low, it can not be matched to the appropriate power supply. Some LED lighting factories have power R & D capabilities, in the beginning of the design of the lamp to evaluate the initial, power design synchronization, you can solve the above problems. In the design, the heat dissipation of the LED and the heat dissipation of the power supply should be comprehensively considered, and the temperature rise of the lamp should be controlled as a whole, so as to design a better lamp.
3. Problems in power supply design
A. Power design. Although the LED light efficiency is high, but there is 80-85% heat energy loss, resulting in a 20-30 degree temperature rise inside the lamp, if the room temperature is 25 degrees, the lamp interior has 45-55 degrees, the power supply for a long time in a high temperature environment, to ensure the life must increase the power margin, generally left to 1.5-2 times the margin.
B, component selection. When the internal temperature of the lamp is 45-55 degrees, the internal temperature rise of the power supply is about 20 degrees, and the temperature near the component should reach 65-75 degrees. Some components will drift at high temperatures, and some will shorten their life, so devices should be selected to be used at higher temperatures 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 whole batch of lights is uneven. And the change of temperature can also cause the output current of the power supply to shift. Generally, the batch error is controlled within +/-5% to ensure the consistent brightness of the lamp. The positive 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 LED series are used, the minimum voltage drop multiplied by the number of series is the lower limit voltage, the maximum voltage drop multiplied by the number of 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 leave 1-2V margin.
D, PCB layout design. LED lamps are left with a smaller size for the power supply (unless it is external to the power supply), so the PCB design requirements are higher, and there are many factors to consider. The safety distance should be left enough, requiring the input and output isolation of the power supply, the primary side circuit and the secondary side circuit are required to withstand 1500-2000VAC, and the distance should be at least 3MM on the PCB. If it is a metal shell lamp, the entire power supply plate should also consider the safety distance between the high voltage part and the shell. 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, potting insulation glue, etc. In addition, the cloth plate should also consider the balance of heat, the heating element should be evenly distributed, and can not be placed centrally to avoid local temperature rise. Electrolytic capacitor away from heat source, slow aging, prolong service life.
E. Authentication problem. At present, there is no domestic standard for LED lamps, the relevant state departments are studying and developing, domestic sales of lamps certification is referred to the standard of lighting lamps, export is to do CE or UL certification, and some refer to foreign LED lamps standards to do. Therefore, in view of this situation, the design of switching power supply to meet the above standards at the same time is more difficult, we can only meet different requirements for different certifications.
B, component selection. When the internal temperature of the lamp is 45-55 degrees, the internal temperature rise of the power supply is about 20 degrees, and the temperature near the component should reach 65-75 degrees. Some components will drift at high temperatures, and some will shorten their life, so devices should be selected to be used at higher temperatures 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 whole batch of lights is uneven. And the change of temperature can also cause the output current of the power supply to shift. Generally, the batch error is controlled within +/-5% to ensure the consistent brightness of the lamp. The positive 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 LED series are used, the minimum voltage drop multiplied by the number of series is the lower limit voltage, the maximum voltage drop multiplied by the number of 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 leave 1-2V margin.
D, PCB layout design. LED lamps are left with a smaller size for the power supply (unless it is external to the power supply), so the PCB design requirements are higher, and there are many factors to consider. The safety distance should be left enough, requiring the input and output isolation of the power supply, the primary side circuit and the secondary side circuit are required to withstand 1500-2000VAC, and the distance should be at least 3MM on the PCB. If it is a metal shell lamp, the entire power supply plate should also consider the safety distance between the high voltage part and the shell. 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, potting insulation glue, etc. In addition, the cloth plate should also consider the balance of heat, the heating element should be evenly distributed, and can not be placed centrally to avoid local temperature rise. Electrolytic capacitor away from heat source, slow aging, prolong service life.
E. Authentication problem. At present, there is no domestic standard for LED lamps, the relevant state departments are studying and developing, domestic sales of lamps certification is referred to the standard of lighting lamps, export is to do CE or UL certification, and some refer to foreign LED lamps standards to do. Therefore, in view of this situation, the design of switching power supply to meet the above standards at the same time is more difficult, we can only meet different requirements for different certifications.
4. Use parameters
The selection of the purchased power supply mainly depends on the constant current and the voltage range of the constant current. The constant current value is selected as the standard current lower of the LED. The choice of voltage range should be moderate, try not to choose a large range, to avoid waste of power.
Specific options recommended:
In LED lighting design, there are generally two kinds of drive schemes: linear drive and switch type drive.
In LED lighting design, there are generally two kinds of drive schemes: linear drive and switch type drive.
Linear driving application is one of the simplest and most direct driving applications. In the application of lighting grade white LED, although there are problems such as low efficiency and poor adjustability, but because of its simple circuit and small size, it can meet some specific applications.
The switch type drive can obtain good current control accuracy and high overall efficiency, and the application mode is mainly divided into two categories: buck type and boost type. Step-down switching drivers are for applications where the power supply voltage is higher than the end voltage of the LED or where multiple leds are driven in parallel. The boost switch driver is for applications where the power supply voltage is lower than the end voltage of the LED or where multiple leds are driven in series.
It is generally believed that the isolated drive is safe but less efficient, and the non-isolated drive is more efficient, which should be selected according to the requirements of actual use.
The current design of the general basic LED driver lighting application is relatively simple, but if other features such as phase control dimming and power factor correction (PFC) are also required, the design becomes complicated. Non-dimming LED drivers with no power factor correction typically include an off-line switching power supply to adjust the output at a constant current.
The back-end architecture of the LED driver contains a current regulation circuit with short circuit protection. This can be achieved using linear regulation circuits, but this method is inherently inefficient and therefore suitable for low output currents, and is not usually applied to multi-level architectures. The alternative is to use a simple step-down regulator circuit with current feedback to limit the output current beyond the desired LED drive current. It counteracts changes in the total LED forward voltage with temperature and device tolerance, and also limits the current in the event of a short circuit or other fault conditions, thereby protecting the driver from damage.
