Summary of four problems in the design of the hott

Summary of four problems in the design of LED drive power supply

the quality of LED drive power supply will directly affect the service life of 230kg led. Therefore, how to make a good LED drive power supply is the top priority of LED power supply designers

in current life, in order to save energy and power, LED has been greatly promoted, but led needs a power driver, and its quality will directly affect the service life of LED. Therefore, how to do a good LED driving power supply is the top priority of LED power designer. This paper introduces some problems of LED driving power supply, hoping to provide some help to engineers

1. The driving circuit directly affects the service life of LED

the LED drive we mentioned includes digital drive and analog drive. Digital drive refers to digital circuit drive, including digital dimming control, RGB full-color change, etc. Analog drive refers to analog circuit drive, including AC constant current switching power supply and DC constant current control circuit. The driving circuit is composed of electronic components, including semiconductor components, resistors, capacitors, inductors, etc. these components have a service life. The failure of any device will lead to the failure of the whole circuit or part of the function failure. The service life of LED is 10000 hours. If it is continuously lit according to 50000 hours, it has a service life of nearly 6 years. The service life of switching power supply is difficult to reach 6 years. The warranty period of * * switching power supply on the market is generally years. The power supply with a 6-year warranty is military grade, and the price is 4 times that of ordinary power supply, and more importantly -6 times. It is difficult for ordinary lamp manufacturers to accept. Therefore, the faults of LED lamps are mostly driving circuit faults

2. Heat dissipation problem

led is a cold light source, the working junction temperature cannot exceed the limit, and a certain margin should 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 and so on. It is necessary to find a balance among many factors, so that the overall lamp is the best. The development time of LED lamps and lanterns is not long, and there are not many experiences that can be used for reference. Many designs are constantly improved. The power supply used by some LED lamp manufacturers is outsourced or outsourced, and the lamp designer does not know much about the power supply. The heat dissipation space for the LED is large, and the heat dissipation space for the power supply is small between the air in the discharge pump (and a little oil). Generally, it is necessary to find a suitable power supply after designing the lamps, which brings certain difficulties to the power supply. It is often encountered that due to the small internal space or high internal temperature of the lamp, and the low cost control, it is impossible to allocate a suitable power supply. Some LED lamp manufacturers have the ability of power research and development. The above problems can be solved by evaluating at the initial stage of designing lamps and designing power synchronously. In the design, we should comprehensively consider the heat dissipation of LED and power supply, and control the temperature rise of lamps as a whole, so as to design better lamps

3. Problems in power design

a. power design. Although the LED has high luminous efficiency, there is still% heat loss, resulting in a temperature rise of ($10.6626) degrees inside the lamp. If the room temperature is 25 degrees, there is a temperature rise inside the lamp. The power supply works in a high temperature environment for a long time. To ensure its service life, it is necessary to increase the power margin, which is generally reserved to 1 Times the margin

b, component selection. In the case of the internal temperature of the lamp, if the internal temperature rise of the power supply is still about 20 degrees, the temperature near the element should reach degrees. Some components' parameters will drift at high temperature, and some components' service life will be shortened. Therefore, devices should be selected that can be used for a long time at higher temperature, and special attention should be paid to electrolytic capacitors and wires

c, electrical performance design. The parameter design of switching power supply for LED is mainly constant current parameter. The size of current determines the brightness of LED. If the batch current error is large, the brightness of the whole batch of lamps is uneven. Moreover, 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. There is deviation in the forward voltage drop of the LED. 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 of serial connections is the lower limit voltage, and the maximum voltage drop multiplied by the number of serial connections is the upper limit voltage. The constant current voltage range of the power supply is slightly wider than this range. Generally, V margin is reserved for the upper and lower limits

d, PCB layout design. The size of LED lamps left for the power supply is small (unless it is external to the power supply), so there are high requirements in PCB design and many factors to be considered. The safety distance should be enough. The power supply with input and output isolation is required. The primary side circuit and secondary side circuit require voltage withstand vac. PCB Sandvik is also one of the few manufacturers in China that can produce high-quality U-tubes. At least 3mm distance should be left. If it is a lamp with a metal shell, the safety distance between the high-voltage part and the shell should also be considered for the layout of the whole power supply. If there is no space to ensure a safe distance, other measures should be taken to ensure insulation, such as punching holes in PCB, adding insulating paper, pouring insulating glue, etc. In addition, the heat balance should be considered for the cloth plate. The heating elements should be evenly distributed and cannot be placed centrally to avoid local temperature rise. Electrolytic capacitors are far away from heat sources, which can slow down aging and prolong service life

e, authentication problems. At present, there is no standard for LED lamps in China, and relevant national departments are studying and formulating. The certification of lamps sold in China is based on the standards of lighting lamps, while those sold abroad are CE or UL certification, and some are based on foreign LED lamp standards. Therefore, 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 voltage range of constant current and constant current. The constant current value is selected as the standard current of LED is lower. The selection of voltage range should be moderate, and try not to choose a larger range to avoid the waste of power