The quality of LED drive power supply will directly affect the life of LED, so how to do a good job of LED drive power supply is the most important of the LED power designer.
In the life, in order to save energy, LED has been popularized, but led to a power driven, its quality will directly affect the LED life. Therefore, how to do a good job a LED driving power supply is led power supply designers of heavy weight. This paper describes some of the LED driver power supply problems, hoping to provide a little help to the engineer.
1, LED drive power directly affect life
The LED drive power supply comprises a driving digital and analog drive, digital drive of the driver that the digital circuit, including digital adjustable light control, RGB color changes. Analog driver refers to analog circuit driver, including the AC constant current switching power supply, DC constant current control circuit. The driving circuit is composed of a semiconductor device, a semiconductor element, a resistor, a capacitor, an inductor, etc., and the service life of the components, any failure of the device can cause the failure of the whole circuit or part of the function failure. LED service life is 5-10 million hours, according to the 50 thousand hours count, continuous light, there are nearly 6 years of life. The service life of the switch power supply is difficult to achieve 6 years, market * * of the switching power supply warranty period is generally 2-3 years, reached 6 years warranty power is the military level, the price is 4-6 times the ordinary power, the general lighting factory is very difficult to accept. So the fault of LED lamps and lanterns is much for driving circuit fault.
2, the heat problem
LED for the cold light source, the operating junction temperature can not exceed the limit, the design must leave a certain margin. The whole lamp design should consider beautiful appearance, convenient installation, light distribution and heat dissipation and so on many aspects to seeking for the balance point in the numerous factors, so that the whole lamp is best LED lamp development time is not long, not many can learn from the experience, a lot of design are constantly improve. Power used in some LED lamp manufacturers association or purchased, lighting designer of power understanding not much, to LED thermal dissipation space is larger, to power of less space for heat dissipation. In general is a good design of lamps and then find a suitable power supply to matching, so that the power supply to bring a certain difficulty. The internal space of the lamp is often encountered because of the small space or the internal temperature is higher, and the cost control is low, can not be matched to a suitable power supply. Some LED lighting plant has power R & D capability, in the beginning of the initial design of the evaluation, the power supply design synchronization, you can solve the above problems. In the design to consider the LED's heat and power supply, the overall control of the temperature rise, so as to design a better lighting.
3, power design problems
A, power design. Although the LED luminous efficiency high, but there are still 80-85% of heat loss, resulting in the ascending temperature 20-30 degrees $10.6626 inside the lamp, if room temperature of 25 degrees, the lamps and lanterns is 45-55 degrees, the power for a long time to work in high temperature environment, to guarantee the service life must increase the margin of power, left in general to 1.5-2 times the margin.
B, component selection. Lamp internal temperature 45-55 degrees, the internal temperature rise is about 20 degrees, the temperature near the component to reach 65-75 degrees. Some elements in the high temperature parameters will drift, some will shorten the life, so the devices to can be used in high temperature for a long time, with particular attention to the electrolytic capacitors and conductors.
C, electrical performance design. Switching power supply for LED parameter design, the main is the constant current parameters, the current size determines the brightness of LED, if the bulk current error is large, then the whole batch of brightness is not uniform. And temperature changes can also cause the power output current offset. Is generally within the batch error control in +/-5%, in order to ensure that the brightness of the lamp is consistent with the.LED forward voltage drop, the power supply design of the constant current voltage range to include the LED voltage range. A plurality of LED series, minimum pressure drop is multiplied by the serial number for lower voltage and maximum voltage drop multiplied by serial number for the upper limit of the voltage, the power supply constant current voltage range to than the slightly more wide and general upper and lower limits of the left margin 1-2V.
D, PCB layout design of LED lamps and lanterns left power of smaller size (unless an external power supply), so in the PCB design requirements higher, to consider the factors. Safe distance to be left enough to require input and output isolation of the power supply, the first side circuit and the two side circuit requires a voltage of 1500-2000VAC, at least on the PCB to stay enough 3MM distance. If the lamp metal casing, the power supply board should also consider the safety distance of high voltage part and shell. If there is no space to ensure a safe distance from to use other measures to guarantee the insulation, such as punch a hole on the PCB, and insulating paper, potting insulating glue. In addition the board should also consider the heat balance, the heating element should be evenly distributed, not centrally located, avoid the local temperature. The electrolytic capacitor is far away from the heat source, slow down the aging and prolong the service life.
E, certification issues. Currently no standards for LED lamps and lanterns, the relevant departments of the state is to study the formulation and the lamps and lanterns of domestic sales certification is the reference standard of lighting lamps and lanterns, the export is to do CE or UL certification, also some reference foreign LED lamp standard to do. So in view of this situation, the design of switching power supply to meet these standards at the same time is more difficult, we can only meet different requirements for different requirements.
4, the use of parameters
Purchased power mainly depends on voltage range of constant flow and constant flow in the choice of. The constant current value is selected as the standard current of LED. The choice of voltage range should be moderate, as far as possible.
