LED driver power supply designed four questions
LED drive power supply quality is good or not 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.
In the current life, in order to save energy, LED by large, but LED all need to have a power drive, its 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.
1、Drive circuit directly affect LED lights life
LED drive including digital drive and simulate the drive and 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, 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.
2、Heat dissipation problems
LED cold light source, work junction temperature cannot exceed the limit, when the design should leave some allowance. The whole design of lamps and lanterns should consider good appearance, easy installation, with light, heat and so on many aspects, to seek a balance in a variety of factors, so that the overall lamps and lanterns is the best. The LED lamps and lanterns is the development of the time is not long, can draw lessons from the experience of not much, a lot of design is constantly improving. Some LED lights 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 are 80-85% of heat loss, the rise of temperature of the LED lamps and lanterns with 20-30 degrees, if the room temperature is 25 degrees, there are 45 to 55 degrees, inside the lamp power supply work in high temperature environment for a long time, to ensure that the life will have to increase the power allowance, allowance for 1.5 2 times.
b、Component selection. Lamps and lanterns of internal temperature of 45 to 55 degrees, internal temperature rise and power about 20 degrees, is near the temperature to 65-65 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 within + / - 5% error control, to ensure that the brightness of the light. LED the positive pressure drop is misaligned, design of constant current power supply 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, generally 1 to 2 v allowance on four floor.
d、PCB board design. LED lamps and lanterns to the power of smaller (external) unless the power supply, so higher requirements on the PCB design, 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 required pressure 1500-2000 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、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.
