LED chip and power installed together, the general space is narrow, poor heat dissipation conditions, how to ensure the quality and life of LED power, it is necessary to consider from the beginning of the design, so as to avoid LED power failure quickly, it can be said that LED power life is the key to restrict the development of LED.
This is the following system design and consideration of the comprehensive problem.
We believe that the performance that affects the life of LED power supply includes environmental characteristics, components and electricity to be collected, including the following aspects:
1. Influence of practical application environment: high humidity environment, high temperature environment, dusty environment, strong magnetic environment, vibration environment
2. Influence of lighting temperature environment: the internal temperature of lighting is less than 65 degrees, the housing of lighting is less than 75 degrees, and the temperature of power supply is less than 60 degrees
3. Influence of power supply network: the voltage input of unstable power network will impact the components of LED power supply, thus affecting the service life pulse of LED drive.
4. Influence of insulation and installation: the correct installation and good insulation of the product will enhance the application power of LED power.
5, the impact of electrolytic capacitor: the sealing position of the electrolytic capacitor will leak out of the gasified electrolyte, this phenomenon will be accelerated with the rise of temperature, it is generally believed that every 10℃ rise in temperature, the leakage speed will increase to 2 times.
So electrolytic capacitors determine the life of a power supply unit.
If the high-temperature electrolytic capacitor with a life span of 10,000 hours and 105 ° c is selected, according to the current life estimation formula of electrolytic capacitor, "every 10 ° c reduction doubles the life", then its working life is 20,000 hours in 95 ° c environment and 40,000 hours in 85 ° c environment.
The normal working life of LED drive power depends on the life of the electrolytic capacitor used in the power supply, and the life of the electrolytic capacitor depends on the life and working temperature of the capacitor itself.
The life of capacitor at 65℃ can only guarantee about 80,000 hours; The life of capacitor at 75℃ can only guarantee about 40,000 hours; The life of capacitor at 85℃ can only guarantee about 20,000 hours; The life of capacitor at 95℃ can only be guaranteed for about 10,000 hours; From the above calculation: the life of electrolytic capacitor will be halved for every 10℃ rise in temperature.
6. Influence of switching times: most power supplies are equipped with the rectifier circuit of capacitor input type, which will generate surge current when entering the power supply, leading to switch contact fatigue, increasing contact resistance and adsorption and other problems. Theoretically, the switch can be switched on and off about 10,000 times during the life expectancy of the power supply.
7. Impact current protection resistance and thermistor's influence: in order to offset the impact current generated when the power supply enters, the design of the power supply usually USES the resistance in parallel with SCR and other elements.
When the power supply is on, the peak power value is up to tens to hundreds of times of the rated value, which results in thermal fatigue of the resistance and causes circuit breaking. In the same case, thermistors will produce thermal fatigue phenomenon.
Isolated and non-isolated
In the general LED lighting market, there are two types of driving power: unisolated design and isolated power supply.
The uninsulated design is limited to dual-insulation products, such as alternatives to light bulbs, where leds and the entire product are integrated and sealed in non-conductive plastic, so that the end user is not at any risk of electric shock.
Secondary products are isolated and relatively expensive, but they are essential where the user has access to LED and output wiring (usually in the case of LED lighting and street lighting applications).
An LED drive power supply with an isolating transformer or electrical isolation means that leds can be touched directly by hand without being electrocuted.
While the LED driving power without isolation transformer can still achieve partial mechanical insulation with the help of protective shell, but the LED at this time cannot be directly contacted when working.
Insulated bulb will become the mainstream in the future
The physical design determines whether the driver is isolated or not.
Security rules usually require two separate isolation layers.
Designers can choose between two physical insulation layers, a plastic astigmatic and a glass shield, and use a non-isolating power source. If physical isolation is too expensive, mechanically difficult, or absorbs too much light, electrical isolation must be addressed in the power supply.
Isolated power sources are usually larger than non-isolated power sources of the same power level. Lighting designers have to do a lot of cost and design optimization in every product they design.
Because apply to different application, it is the insulation transformer that USES isolation or the protective chimney shell that USES isolation, stylist considers to be able to have different view forever in different Angle.
Usually, they will analyze various aspects, such as cost and manufacturing process, efficiency and volume, insulation reliability and safety specification requirements, and so on. The driving cost of transformer is relatively high, but it also makes LED lamps more practical and can meet the needs of end users who accidentally contact LED. When the incandescent glass case is easily damaged, an ordinary E27 bulb can be replaced with an LED.
In addition, lamps in industrial areas or office equipment applications do not need to reach the end user, such as street lamps and shopping mall lighting. At this time, LED lamps do need isolation transformers.
As a product that can be used safely by end users, the reliability of insulation and isolation must be considered.
As a complete product, the part of the surface that can be touched by the user must be isolated and cannot be electrocuted. In terms of the whole system of the product, isolation is inevitable. The difference is only that the location of isolation is different.
Some designers use isolated transformer designs, so they can simplify cooling and lampshades. Reliable insulation requirements must be considered in structures such as lamp housings if the drive is designed without isolation. As a result, as power - driven, isolated and non - isolated solutions have always existed.
The main challenge that Chinese LED power supply manufacturers may face is to find low-cost AC/DC drivers that meet the requirements for more stringent power factor and efficiency performance in low-cost power supply systems.
In the future, it will no longer be free to use high-quality, reliable power sources in systems with limited space and difficult cooling, such as LED lamps. However, until the end user has used many of the bulbs with a life span of around 10,000 hours, it is difficult to prove that they are of high quality.
Transformer - based isolated LED drive power supply will be the mainstream
Isolated and unisolated LED drive power schemes have their own advantages and disadvantages.
Industry insiders think ClassII will become mainstream, as it simplifies LED cooling. ClassI or II systems rely on grounding systems and, in most cases, depend on where they are installed.
ClassII is relatively common, and it requires double-stage or enhanced isolation, that is, transformer magnetic winding, insulation band and physical isolation. ClassI requires an earthing shell and/or mechanical ClassII barriers, which are not required by the ClassI system.
Several trends are driving the LED lighting market. The first is the continuous improvement in the efficiency of high brightness leds and the emergence of highly efficient and reliable constant current LED driving power supply, followed by the global legislation to ban incandescent lighting (due to its inefficiency) and the gradual fading out of CFL energy-saving lamps (if broken, it will discharge harmful mercury to the environment).
Together, these factors are making LED lighting a long-term trend.
Of course, low system costs (including leds, thermal management systems, and LED drivers) will always be the driving force behind the widespread adoption of LED universal lighting by consumers.
In fact, in many LED lighting products, failure is a common phenomenon, mostly due to power failure, rather than LED failure. At the design level, you have to become an expert in the thermal design of the system.
Leds provide high efficiency, but they also generate more heat transfer than incandescent or energy-saving bulbs.
Since many LED lighting applications are enclosed in a small space, it is difficult to ventilate the heat.
Without careful thermal design, leds and power drive circuits can easily degrade or fail permanently due to high temperatures.