Parsing of LED lighting driver power supply problems
in order to saving energy save electricity, LED by large, but LED all need to have a power drive, it is good or bad will directly affect the service life of the LED, so how to make an LED driving power supply is the key of the LED power supply designer. This paper introduces some problems of LED drive power supply, engineers to provide a little help.
1, the drive circuit directly affect LED life
what we call the LED drive including digital drive and simulate the drive and the digital circuit driver drive index word, including digital dimming control, RGB full color changes, etc. Refers to the analog circuit to simulate the drive and drive, including AC constant current switching power supply, DC constant current control circuit. Driver circuit is composed of electronic components, including semiconductor devices, resistor, capacitor, inductor, etc. , these components have life, any device failure will lead to the failure of the whole circuit or part function failure. The service life of the LED is 5 - 100000 hours, calculate by 50000 hours, continuous light, nearly six years of life. The life of the switch power supply is difficult to achieve for six years, sale of switching power supply on the market is generally 2 - warranty period The power of the 3 years to 6 years quality assurance is the military level, price is 4 - normal power supply The lamps and lanterns of 6 times, general factory is difficult to accept. So the LED lamps and lanterns of failure are driving circuit failure.
2, heat dissipation problems
LED cold light source, work junction temperature cannot exceed the limit, when the design will have a certain margin. The whole design of lamps and lanterns should consider good appearance, easy installation, with light, heat and so on many aspects, to seek balance in many factors, so that the overall lamps and lanterns is the best. LED lamps and lanterns, development time is not long, can draw lessons from the experience of not much, a lot of design is constantly improving. Some LED lamps factory power supply for outsourcing or outsourcing, don't know much about the lighting designer to power supply, to the LED heat dissipation space is larger, to power the heat dissipation space is smaller. Is generally good design of lamps and lanterns and then to find the right power supply to form a complete set, bring certain difficulty to the power of form a complete set. Often encounter because of small space inside the lamp or the internal temperature is higher, and the cost control is low, cannot match to a suitable power source. Some LED lamps factory have power research and development ability, to evaluate at the beginning of the beginning design of lamps and lanterns, the power of the simultaneous design, can solve the above problems. In to consideration in the design of the LED heat dissipation of heat and power supply, the overall control the temperature of lamps and lanterns, in order to design a good lamps and lanterns.
3, problems in the design of power supply
a, power design. While LED luminous efficiency is high, but there is 80 - 85% of heat loss, which has 20 - inside the lamp The rise of temperature of the 30 degrees, if the room temperature is 25 degrees, there are 45 - inside the lamp 55 degrees, the power supply work in high temperature environment for a long time, to ensure that the life will have to increase the power allowance, generally until 1. 5 - 2 times the allowance.
b, element selection. 45 - internal temperature of lamps and lanterns 55 degrees, internal temperature rise and power about 20 degrees, is near the temperature reaching 65 - 75 degrees. Some components will drift in high temperature condition parameters, and some will shorten the service life, so the device to select can be used in high temperature for a long time, pay special attention to electrolytic capacitor and wires.
C, electrical design. Switching power supply for LED parameter design, mainly is the constant current parameter, the size of the current decision LED brightness, if the current batch error is larger, the whole batch of the brightness of the light is not uniform. And the change in temperature can also cause the power supply output current offset. Usually batch error control at + / - Less than 5%, can ensure the brightness of the light. Positive pressure drop is misaligned, LED power supply design of constant current voltage range to include the LED voltage range. Multiple LED string using time, the minimum pressure drop multiplied by the string of threshold voltage, the maximum pressure drop connecting multiplied by the number of upper limit voltage, the power of the constant current voltage range slightly wider than the range, the leave 1 - general upper and lower limits 2 v allowance.
d, PCB board design. The size of the LED lamps and lanterns to power small ( Unless it is power source external) On PCB design, so the demand is higher, want to consider more factors also. Should stay a safe distance from enough, for the power of the input and output isolation, a side and secondary side circuit pressure 1500 - requirements 2000 vac, at least on the PCB to keep enough distance to 3 mm. If is the lamps and lanterns of metal case, cloth plate consider high pressure part of the whole power supply and the shell of a safe distance. If there is no space to ensure a safe distance from the case to use other measures to ensure insulation, such as punching on PCB, insulation paper, insulation potting glue, etc. Another cloth plate to consider heat equilibrium, heating element to uniform distribution, cannot be placed centrally, avoid local temperature rise. Electrolytic capacitor away from heat source, slow down aging, prolong service life.
e, authentication problem. There is currently no standard for the LED lamps and lanterns, the domestic country is to formulate the relevant departments, the lamps and lanterns of domestic sales certification is referring to the standard of lighting lamps and lanterns, CE and UL certification, export of do still have some reference to foreign standard of LED lamps and lanterns to do it. So for this kind of situation, the design of switch power supply it is difficult to meet those standards, we can only meet different certification according to different requirements.
4, problems in power applications
5, using parameter
outsourcing power depends mostly on the choice of constant current and constant current voltage range. Constant current value choice for the LED standard current offset. The choice of voltage range wants moderate, try not to choose major, avoid the waste of power.