LED drive power quality will be a direct impact on the life of LED, so how to do a LED driver
power supply is the top priority of LED power supply designers.
In the current life, in order to save energy and energy, LED has been a great promotion, but the
LED need to have a power drive, its good or bad will directly affect the life of LED, so how to do
a LED driver power supply is LED power supply designer The top priority. This article describes
some of the LED drive power problems, hoping to provide some help to the engineers.
1, the drive circuit directly affects LED life
We said the LED driver, including digital drive and analog drive two types, digital-driven exponen-
tial circuit driver, including digital dimming control, RGB full color changes and so on. Analog
drive refers to the analog circuit driver, including AC constant current switching power supply,
DC constant current control circuit. The drive circuit consists of electronic components, including
semiconductor components, resistors, capacitors, inductors, etc., these components have a service
life, any one device failure will lead to failure of the entire circuit or part of the function
failure. LED life is 5-10 million hours, according to 50,000 hours count, continuous light, nearly
6 years of life. Switching power supply life is difficult to achieve 6 years, the market switching
power supply warranty period is generally 2-3 years, to 6 years warranty power supply is military
grade, the price is 4-6 times the ordinary power supply, the general The lighting factory is very
difficult to accept. So the failure of LED lamps for the drive circuit failure.
2, heat problems
LED for the cold light source, the working temperature can not exceed the limit, the design should
leave a margin. The design of the entire lamp to consider the appearance of beautiful, easy install-
ation, with light, heat and many other issues, to find a balance in many factors, so that the over-
all lighting is the best.LED lamps development time is not long, you can learn from Of the experience
is not much, many designs are constantly improved. Some LED lighting manufacturers use power for
outsourcing or outsourcing, lighting designers know little about the power to the LED cooling space
larger, to the power of the cooling space is small. Usually after the design of a good light to
find the right power to match, so give the power supply to bring some of the difficulties. Often
encountered due to the smaller internal space or internal temperature is higher, and the cost contr-
ol is low, can not be equipped with the appropriate power. Some LED lighting factory has power
research and development capabilities, in the beginning of the design of the initial assessment of
the lamp, power supply design synchronization, will be able to solve the above problems. In the
design to take into account the LED cooling and power supply cooling, the overall control of the
temperature rise of lamps, so as to design a better lamp.
3, power supply design problems
A, power design. Although the LED light effect is high, but there are 80-85% of the heat loss,
resulting in light inside the 20-30 ($ 10.6626) degrees of temperature rise, if the room temperat-
ure of 25 degrees, the situation, the lamp has 45-55 degrees, Long time in high temperature enviro-
nment, to ensure that life must be increased power margin, generally left to 1.5-2 times the margin.
B, component selection. Lamp internal temperature of 45-55 degrees, the internal temperature rise
of about 20 degrees, then the temperature near the component to reach 65-75 degrees. Some components
in the high temperature conditions will drift parameters, and some life will be shortened, so the
device to choose a high temperature for a long time to use, pay special attention to electrolytic
capacitors and wires.
C, electrical performance design. Switching power supply for LED parameter design, mainly constant
current parameters, the size of the current LED brightness, if the bulk current error is large,
the brightness of the entire batch of light is not uniform. And the temperature change can also
cause the power output current offset. Generally, the batch error is controlled within +/- 5% to
ensure that the brightness of the lamp is the same. The forward voltage drop of the LED is deviated,
and the constant voltage range of the power supply design should include the voltage range of the
LED. When the number of LEDs is used in series, the minimum voltage drop is multiplied by the serial
number as the lower limit voltage, the maximum voltage drop is multiplied by the upper limit of the
series voltage, and the constant current voltage range of the power supply is slightly wider than
this range. Stay 1-2V margin.
D, PCB layout design.LED lamps left to the power of the smaller size (unless the power is external),
so the PCB design requirements are higher, to consider the factors are more. Safe distance to stay
enough to require input and output isolation of the power supply, the primary circuit and secondary
circuit requirements withstand voltage 1500-2000VAC, on the PCB to stay at least 3MM distance. If
it is a metal case of the lamp, the entire power supply board also consider the high pressure part
and the safe distance of the shell. If there is no space to ensure safe distance will use other
measures to ensure insulation, such as punching on the PCB, plus insulation paper, potting
insulation, and so on. Another cloth board should also consider the heat balance, heating elements
to be evenly distributed, can not be concentrated, to avoid local temperature rise. Electrolytic
capacitors away from heat, slow down aging, extend the service life.
E, certification issues. At present, there is no domestic standards for LED lamps, the relevant
state departments are studying the development of domestic sales of lighting certification is the
reference lighting standards, the export is CE or UL certification, and some reference to foreign
LED lighting standards to do. Therefore, in view of this situation, the design of switching power
supply to meet the above criteria at the same time is more difficult, we can only meet the different
requirements for different certification.
4, the use of parameters
External power supply in the choice of the main constant current and constant current voltage
range. The constant current value is chosen to drop the standard current of the LED. The choice
of voltage range should be moderate, try not to choose a larger range, to avoid the waste of power.