There are several trends are driving the development of LED lighting market. First of all is the high brightness LED efficiency of continuous improvement and very high reliability and high reliability of constant current LED driver power supply continues to emerge, followed by the global legislation to ban incandescent lighting (due to its low efficiency) and CFL energy-saving lamps gradually fade out (if broken, it will flow out of the environment harmful mercury). These factors are combined to make LED lighting become a long-term development trend. Of course, low system cost (including LED, thermal management system and LED driver) will always be the driving force for the wide use of LED general lighting. In fact, in many LED lighting products, failure is a common phenomenon, most of which is because of the failure of the power, rather than the failure of LED. At the design level, this means that the OEM must become a hot design expert. LED provide high efficiency, but they are also more heat than incandescent or energy-saving lamps. Because many LED lighting applications are enclosed in a very small space, it is difficult to use ventilation to heat dissipation. If there is no careful thermal design, the LED and the power drive circuit is easy because of high temperature and degradation or permanent failure.
As a product that allows the end user to be safe, it must consider the reliability of insulation and isolation. As a complete product, the surface of the product can be exposed to the part of the user must be isolated, can not let people get electric shock. And from the whole system, the isolation is inevitable, the difference is only set the location of the isolation. Some designers use isolated transformer design, so they can simplify the design of cooling and lamp shades. If you use non isolated driver design, the lights on the shell structure of the insulation requirements must be considered reliable. As a result of power supply, the isolation and non isolation schemes are all the same. The main challenge for the Chinese LED drivers is to find a low cost AC/DC driver, which can meet the performance of more stringent power factor and efficiency in low cost power supply system. In the future, the use of high quality, high reliability power supply will be no longer free of charge in the space constrained and there is a cooling system (such as LED lamps). However, in the end users have used a lot of life in 10000 hours or so…
LED driver power isolation and non isolation 7-5 is currently in the general LED lighting market, there is a non isolated design and isolated power supply. Non isolation design is limited to a dual insulation product, such as a light bulb replacement product, where the LED and the entire product are integrated and sealed in a non conductive plastic, so the end user does not have any risk of electric shock. The two level products are isolated, the price is relatively expensive, but in the user can be exposed to the LED and the output connection (usually in the case of LED lighting and street lighting applications), this product is essential. LED driver power supply with isolation transformers or electrical isolation means that the LED can be directly touched by hand without electric shock. Without the isolation transformer LED drive power still can with protective casing, so as to realize the mechanical part of the insulation, but this time the LED at work and not direct contact. Insulation type light bulb in the future will become the mainstream. Physical design determines that the drive is an isolated or a non – isolated. Safety rules usually require the use of two separate isolation layers. The designer can choose two kinds of physical isolation layer, or plastic mask and glass cover, and use of non isolated power supply. If the cost of physical isolation is too high, there is a mechanical difficulty or absorb too much light, it is necessary to solve the problem of electrical isolation in power. Isolated power supply is usually more than the same power level of non isolated power supply. Lighting designers must be in the design of each product in a lot of cost and design optimization work. Because it is suitable for different applications, it is a protective shield that is used in isolation. In general, they will be analyzed in many ways, such as cost and manufacturing process, efficiency and volume, reliability and safety requirements, and so on. With the high cost of the transformer, but also to make the LED lamps become more practical, to meet the needs of the end user to meet the needs of LED. When the incandescent lamp glass shell is easy to damage, a E27 type of ordinary light bulb can be replaced with LED lights. In addition, in the industrial area or office equipment in the application of the lamps do not need to contact the end user, such as street lamps and shopping malls lighting, then the LED lights do need to isolate the transformer.
IP is internationally used to identify the protection level of the code Ip level by two figures, the first digital representation of dust; second figures from the representation of water, the greater the number of figures, said the leader is better.
Definition of number protection
0 no protection without special protection
1 to prevent the body from more than 50mm to prevent the human body due to accidentally touch the internal parts of the lamp to prevent the diameter greater than 50mm of the object
2 to prevent the object from more than 12mm to prevent the internal parts of the finger to prevent the finger
3 to prevent more than 2.5mm of the whole body to prevent the intrusion of the diameter is greater than the 2.5mm tool, wire or object intrusion
4 more than 1.0mm objects to prevent intrusion prevention diameter greater than 1 of mosquitoes, insects or invasive objects
5 dust can not completely prevent dust intrusion, but the amount of dust will not affect the normal operation of the lamp
6 dust completely prevent dust intrusion
Definition of number protection
0 no protection without special protection
1 to prevent the drip of water from the vertical drop
2 tilt 15 degrees when the lamp is still to prevent water intrusion when the lamp is tilted 15 degrees, can still prevent dripping
3 to prevent the injection of water intrusion into the water, or the vertical angle is less than 50 degrees in the direction of the water jet
4 to prevent the splash of water intrusion prevention of the direction of the water intrusion
5 waves of water to prevent intrusion prevention or blowhole rapidly from waves of water intrusion
6 to prevent water intrusion into the water waves lamps in a certain period of time or pressure conditions, to ensure the normal operation of the lamp can be
7 to prevent the intrusion of water into the lamp without a period of water in a certain water pressure, and can ensure the normal operation of the lamp
8 to prevent the impact of the sinking
Two about 1 breakdown and protection
Two reasons for the 1.1 breakdown
The two time breakdown is mainly due to the high local temperature caused by the device. The reason for the increase in temperature is that the thermal imbalance is caused by the forward bias, and the reverse bias is caused by the avalanche breakdown.
Because of the thermal resistance of the transistor in the pipe internal distribution is uneven, in some weak areas, the temperature rise will be higher than other parts, forming the so-called hot, local temperature caused by the local current increases, the current increases, so that the temperature rise, so the cycle until a critical temperature, resulting in the breakdown of the tube.
The two breakdown caused by avalanche breakdown is due to the occurrence of an avalanche breakdown, at some point due to the current density is too large, the change of the electric field distribution, resulting in negative resistance effect, so that the local temperature is too high a phenomenon.
1.2 measures to avoid the two breakdown
Opening and closing loss are important factors to affect the normal operation of switching devices. Especially in the dynamic process of the transistor is easy to produce two breakdown phenomenon, this phenomenon is directly related to the switch loss, so it is necessary to reduce the switching loss of the device is the proper use of the device. To reduce the loss can be achieved through two ways to achieve:
(1) to low collector emitter voltage to turn off transistor (Vce);
(2) in the process of the rising of the emitter voltage, the transistor must be reduced to minimize the emitter current. The introduction of the buffer circuit is one of the ways to achieve the above purpose.
1.3 buffer circuit in switching power supply
In the design of the switching power supply, the following buffer circuit can be used to ensure that the transistor runs in the safe zone (SOA).
1) the use of the off buffer circuit is a kind of energy dissipation and off buffer circuit. Although it has more energy consumption, but the circuit is simple.
Two) 2 commonly used energy dissipation type open circuit.
A. has a non saturation reactance of the open circuit (Figure 2): the inductance – diode network with the transistor collector in series, the formation of a buffer circuit. When the tube is open, the Ls control current of the inductor is DT di/. When the tube is turned off, the energy 1/ 2 (LsI2m), which is stored in the inductor Ls, is continuously flowing through the diode Ds, and the energy consumption is dissipated in the resistance of the Ds and the reactor.
B. has a saturable reactor (Figure 3): the purpose of the opening of the buffer circuit is in order to make the transistor in the open collector current, the collector voltage drops to 0, in order to make the opening loss minimum. Especially for inductive load effect is more significant. Design of saturable reactor should be done: collector voltage drops to zero, the buffer reactor in saturation state; before saturation, collector voltage down to zero before, the reactor is high resistivity, magnetization current flowing through a tube is very small so as to achieve the purpose to reduce switching loss.
VS+: half the output voltage of the power supply
VS-: dual core and dual core
VCO: voltage controlled oscillator
Identifier of VCI: virtual channel
The total solar radiation of PAR: in the range of 400~700nm
INH: no end