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LED lighting is a rare and no pollution green light, made up of solid state semiconductor devices, and it can turn electrical energy into light. Compare with traditional incandescent bulb, fluorescent lamps, LED light bulb with smaller size, lower power consumption, longer service life, more colors, environmentally friendly and excellent seismic performance. These decided it got a leading-edge position in modern lighting market, and became popular very fast. LED needs a power supply (also called LED driver, which is the heart of this new generation lamp), and its quality will directly affect the life span of integrated lighting fixture. So how to make a perfect power supply for LED is the TOP PRIORITY. In this post we are going to talk about some key points of driver and its design, try to provide some help.
1, the circuit design of power supply directly affects the life of LED light bulb
LED driver divided into two types, digital-driven and analog-driven. Digital-driven means digital circuit driving, such as digital dimming control, RGB full color changes, etc. Analog circuit-driven including AC constant current switching power supply and DC constant current control circuit.
All drivers are made up of electronic components, semiconductors, resistors, capacitors, inductors, and all of these components are have life, any failure would cause the entire circuit down or partial function lose. LED's life time is over 50,000 hours, which means it can continuously lit nearly 6 years. But power supply is very difficult to reach 6 years service time and its warranty generally available at 3 years in present market. Only the military product level switching power supply can have a 6 years warranty, but its price will be 4-6 times of normal power supply, very unfriendly. So the most fault of LED lighting fixture is its driver circuit fault.
2, heat dissipation issues
As a cold light source, LED can't exceed its operating junction temperature limit, and have to set aside a certain allowance when you design LED luminaries. And during the entire design process you have to consider about how to make it in a nice appearance, easy be installed, with an excellent light effect, great cooling system, and many other aspects at the same time, in order to make lamp as best as it could be.
But LED light's history is very short, still on the way to be better and better. Some LED light bulb manufacturers are purchasing driver from other factory, not design driver by them self. Unfortunately their lighting designers don't know the outsourcing power supply very much, so, the light source get a big heat sink space and rest a small part for power supply. Even some of them are design lamp first, and looking for the appropriate power supply after LED luminary housing design already finished. This non-professional action only brings more difficulties and unexpected problems. Due to that small space of lamp, high internal temperature or budget shortfall, they even can't find the right driver.
Some professional manufacturers have ability to research and development their own power supply. THIS IS A GREAT ADVANCE - do lighting design and power supply design at the same, will solve all above problems. Consider the heat dissipation of LEDs and power supply both, to control the whole lamp temperature rises, LED lights' quality will be much better in this way (This is why CREE, PHILIPS, OSRAM design & produce their own brand LED divers - make their light sources in a perfect play, and with the best quality guaranteed).
3, problems may need attention during design LED driver
A, power/wattage. Although LED has a high light efficiency, but it still has 80-85% of heat loss, which make the whole lamp inside temperature higher than outside 20-30 degree. If the room temperature is around 25 degree, the inside of LED light bulb will be 45-55 degree. So, the power supply have to working in a high temperature environment for a long time, and in order to ensure its long life time, the wattage of driver have to be increased as 1.5-2 times for set aside a certain allowance.
B, component selection. If the inside temperature of lamp is 45-55 degree, LED driver's internal temperature will get 20 degree higher, so components' working temperature is 65-75 degree. Some components' parameter will be very high and even get drift, some components' life span get cut. So power supply need high temperature resistance components, especially the electrolytic capacitor and wire.
C, electrical performance design. Driver designed according to the parameter of LED - the constant current data - current determines the brightness of lamp. If a batch drivers have current error, LED lamps will at different brightness cause these drivers (and power supply's temperature change can cause the current change). For ensure the same brightness, driver current error have to be controlled within +/-3%. And consider about that LED's forward voltage has a little bit deviation, so driver's voltage range has to contain it. When multiple LEDs series, minimum voltage drop multiplied by serial number is minimum voltage. Maximum voltage drop multiplied by the serial number is maximum voltage. The constant current power supply voltage range is wider than this range (minimum voltage ~ maximum voltage), usually it is minimum voltage - 2V~maximum voltage + 2V.
D, PCB design. LED lights have no big space for internal driver, so PCB needs an excellent design, and dozens factors need be considered, like the adequate safety distances, power input and output isolation, primary and secondary side circuit need pass high AC 1500~2000V testing, at least have 3MM distance between them. If LED light bulb with a metal housing, the entire PCB design also need consider about the safe distance between high pressure part and metal shell. If there is no space to make a safe distance, you have to use other measures to guarantee the insulation protection, such as make holes on PCB, add insulating paper, pouring insulation adhesive, etc. At meantime, also need consider about the thermal equilibrium and uniformly distribute heating elements, to avoid local overheating. Electrolytic capacitors keep away from high temperature parts to slow down its aging and prolong the service life of it.
