The quality of the LED drive power supply will directly affect the life of the LED, so how to make an LED drive power supply is the top priority of the LED power supply designer.

　　In current life, in order to save energy and electricity, LEDs have been greatly promoted, but LEDs need to have a power drive, which will directly affect the life of the LED, so how to make an LED drive power is the LED power designer The top priority. This article introduces some LED drive power problems, hoping to provide some help to engineers.

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

　　What we call LED driver includes digital driver and analog driver. Digital driver refers to digital circuit driver, including digital dimming control, RGB full-color change, etc. 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, inductances, 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 functional failure. The service life of LED is 50,000 to 100,000 hours. Calculated as 50,000 hours, it is continuously lit and has a lifespan of nearly 6 years. The life of a switching power supply is difficult to reach 6 years. The best switching power supply on the market has a warranty period of 2-3 years. The power supply with a 6-year warranty is military grade, and the price is 4-6 times that of ordinary power supplies. The lighting factory is very difficult to accept. Therefore, the faults of LED lamps are mostly drive circuit faults.

　　2. Heat dissipation problem

　　LED is a cold light source, the operating junction temperature cannot exceed the limit, and a certain margin should be left in the design. The design of the entire 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 is not long, and you can learn from it There is not much experience, and many designs are constantly improved. Some LED lighting manufacturers use power supplies from outsourcing or outsourcing. Lighting designers don’t know much about power supplies. The space for heat dissipation for LEDs is relatively large, while that for power supplies is relatively small. Generally, after the lamps are designed, a suitable power supply is found, which brings certain difficulties to the matching of the power supply. It is 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 equipped with a suitable power supply. Some LED lighting manufacturers have power supply research and development capabilities. The above problems can be solved by conducting evaluations at the beginning of the design of the lighting and the simultaneous design of the power supply. In the design, it is necessary to comprehensively consider the heat dissipation of the LED and the power supply, and control the temperature rise of the lamp as a whole, so that a better lamp can be designed.

　　3. Problems in power supply design

　　a. Power design. Although the LED has high luminous efficiency, there is still 80-85% of heat loss, resulting in a temperature rise of 20-30 ($10.6626) degrees inside the lamp. If the room temperature is 25 degrees, there will be 45-55 degrees inside the lamp, and the power supply will last for a long time. To work in a high temperature environment, the power margin must be increased to ensure the life, and generally leave a margin of 1.5-2 times.

　　b. Component selection. When the internal temperature of the lamp is 45-55 degrees, and the internal temperature rise of the power supply is about 20 degrees, the temperature near the components should reach 65-75 degrees. Some components will drift in high temperature conditions, and some will shorten their lifespan. Therefore, the components should be selected for long-term use at higher temperatures, paying special attention to electrolytic capacitors and wires.

　　c. Electrical performance design. The switching power supply is designed for LED parameters, 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 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 of series connections is the lower limit voltage, and the maximum voltage drop multiplied by the number of series connections 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 LED lamps reserved for the power supply is small (unless the power supply is external), so the PCB design requirements are higher, and there are many factors to consider. The safety distance must be sufficient, and 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 at least a sufficient distance of 3mm on the PCB. If it is a lamp with a metal shell, the layout of the entire power supply should also consider the safe distance between the high-voltage part and the shell. If there is no space to ensure a safe distance, other measures must be used to ensure insulation, such as punching holes in the PCB, adding insulation paper, and potting insulation 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 together to avoid local temperature rise. The electrolytic capacitor is far away from the heat source to slow down the aging and prolong the service life.

　　e. Certification issues. At present, there is no standard for LED lamps in China. The relevant national departments are studying and formulating. The certification of lamps sold in China is based on the standards of lighting lamps, while those for export are certified by CE or UL, and some are based on foreign LED lamp standards. Therefore, in view of this situation, it is difficult for the design of a 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 choice of purchased power supply mainly depends on the voltage range of constant current and constant current. The constant current value is chosen to be lower than the standard current of the LED. The selection of the voltage range should be moderate, try not to choose a larger range to avoid waste of power.