4. Problems in power supply design

(1) Power design.  Although LED light efficiency is high, but there are 80% ~ 85% of heat loss, resulting in 20 ~ 30K temperature rise inside the lamp, if the room temperature is 25℃, the lamp inside is 45 ~ 55℃.  The led power supply works for a long time in high temperature environment. To ensure the life, power margin must be increased, generally retained 1.5 ~ 2 times the margin.  

(2) Component selection.  When the internal temperature of the lamp is 45 ~ 55℃, the internal temperature rise of the power supply is about 20℃, and the temperature of the component will reach 65 ~ 75℃.  Some components in high temperature, its parameters will change, and even the life will be shortened. So the components to choose can sustain working long time at higher temperature, but also pay special attention to electrolytic capacitor and wire.

(3) PCB board design.  LED lamps leave a smaller size for the power supply (unless the power supply is external), so there are higher requirements and more factors to consider in PCB design.  Safe distance should be left enough, input and output isolated power supply, primary side circuit and secondary side circuit should withstand voltage 1500 ~ 2500VAC, at least enough distance of 3mm on PCB.  If it is a metal shell of the lamp, the entire power supply of the cloth board 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 taken to ensure insulation, such as punching holes in the PCB, adding insulating paper, sealing insulation glue, etc.  In addition, the board should also consider heat balance, heating elements should be evenly distributed, can not be placed centrally, to avoid local temperature rise.  Electrolytic capacitor away from heat source, slow down aging, prolong service life.