LED drive power is a voltage converter that converts the power supply to a specific voltage and current to drive the LED to emit light. Generally, the input of the LED drive power includes high-voltage power frequency AC, low-voltage DC, high-voltage DC, low-voltage high-frequency AC (such as electronic Transformer output), etc. The output of the LED drive power supply is mostly a constant current source that can change the voltage as the LED forward voltage drop changes. The core components of the LED power supply include switching controllers, inductors, switching components (MOSfet), feedback resistors, input filter components, output filter components, etc. According to the requirements of different occasions, there must be input overvoltage protection circuit, input undervoltage protection circuit, LED open circuit protection, overcurrent protection and other circuits.
The key to making an LED lighting product is heat dissipation, driving power, and light source. Heat dissipation is particularly important. The heat dissipation effect directly affects the life quality of lighting products. The life of the drive power supply and the stability of output current and voltage The overall quality of life also has a great impact, the light source is the core part of the entire product. The following provides some relevant knowledge of LED drive power.
Constant current drive:
Due to the particularity of LED processing and manufacturing, the current and voltage characteristics of LEDs produced by different manufacturers or even the same manufacturer in the same batch of products have large individual differences. Taking the typical specifications of high-power 1W white LED as an example, a brief description will be made according to the current and voltage changes of the LED. Generally, the forward voltage of 1W white light is about 3.0-3.6V, that is to say, when the standard is called 1W LED When a current of 350 mA flows, the voltage across it may be 3.1V, 3.2V or 3.5V or other values. To ensure the life of 1W LED, general LED manufacturers recommend that the lamp factory use 350mA to go Driven, when the forward current through the LED reaches 350 mA, a small increase in the forward voltage across the LED will greatly increase the forward current of the LED, causing the LED temperature to rise linearly, thereby accelerating the LED light decay , Shorten the life of the LED, even burn out the LED in severe cases. Due to the particularity of the voltage and current changes of LEDs, strict requirements are imposed on the power supply for driving LEDs.
Constant current source driving is the best LED driving method. Constant current source driving is adopted. There is no need to connect a current-limiting resistor in series with the output circuit. The current flowing on the LED is also independent of external power supply voltage changes, ambient temperature changes, and discrete LED parameters. Influence, so as to keep the current constant and give full play to the various excellent characteristics of LED.
The LED constant current power supply is used to supply power to the LED lamps. Since the current flowing through the LED is automatically detected and controlled during the power supply operation, there is no need to worry about excessive current flowing through the LED at the moment of power-on, nor worry about load short-circuit burning. Bad power supply.
Electrolytic capacitor:
Some manufacturers worry that the use of electrolytic capacitors on the power supply driver board will affect the life of the power supply. In fact, it is a misunderstanding. For example: if you choose a high-temperature electrolytic capacitor with a temperature of 105 degrees and a life of 8000 hours, according to the commonly used method of estimating the life of electrolytic capacitors, every 10 degrees , Double the lifespan ", then it has a working life of 16,000 hours in a 95-degree environment, 32,000 hours in a 85-degree environment, and 64,000 hours in a 75-degree environment. If the actual working temperature is lower, Then the lifespan will be longer! From this point of view, as long as the use of high-quality electrolytic capacitors has no effect on the life of the driving power supply.
Heat dissipation:
Because the LED emits a lot of heat during operation, the junction temperature of the die rises rapidly. The higher the LED power, the greater the heating effect. The increase in the temperature of the LED chip will lead to changes in the performance of the light-emitting device and the attenuation of the electro-optical conversion efficiency. In severe cases, it may even fail. According to experimental tests, every time the temperature of the LED rises by 5 degrees Celsius, the luminous flux drops by 3%. Therefore, LED lamps must pay attention to LED For heat dissipation of the light source itself, try to increase the heat dissipation area of ​​the LED light source as much as possible, and reduce the working temperature of the LED itself. If conditions permit, it is best to separate the power supply part from the light source part.
reliability:
Especially like the driving power supply of LED street lamps, it is installed at high altitude, which is inconvenient for maintenance and the cost of maintenance is also large.
effectiveness:
LED is an energy-saving product, and the efficiency of the driving power supply is high. It is very important for the heat dissipation of the power supply installed in the lamp. The efficiency of the power supply is high, its power consumption is small, and the heat generated in the lamp is small, which reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LED.
Power Factor:
The power factor is the load requirement of the power grid. Generally, there is no mandatory index for electrical appliances under 70 watts. Although the power factor of a single consumer with low power is a little low, it has little effect on the power grid, but the amount of lighting used at night is large, and the similar loads are too concentrated, which will cause serious pollution to the power grid. For LED drive power of 30 watts to 40 watts, it is said that in the near future, there may be certain index requirements for power factors.
Surge protection:
The ability of LED to resist surge is relatively poor, especially the ability to resist reverse voltage. It is also important to strengthen protection in this regard. Some LED lights are installed outdoors, such as LED street lights. Due to the induction of the grid load and the induction of lightning strikes, various surges will be invaded from the grid system, and some surges will cause damage to the LED. Therefore, the analysis of the "Zhongke Huibao" drive power supply should have some deficiencies in terms of surge protection. As for the frequent replacement of power supplies and lamps, the LED drive power supply must have the ability to suppress the intrusion of the surge and protect the LED from damage.
Over temperature protection:
In addition to the conventional protection functions of the power supply, it is best to increase the LED temperature negative feedback in the constant current output to prevent the LED temperature from being too high; it must meet the requirements of safety regulations and electromagnetic compatibility. Because the LED emits a lot of heat when it is working, the brightness will also decrease with the increase of heat. When the heat treatment is not serious enough, it will burn the LED lamps and cause a fire. At the same time, the change of LED junction temperature will also bring about the change of voltage, causing the unstable operation of the driver. Therefore, LED drivers need to consider over-temperature protection when designing, and turn off the output if necessary to prevent danger.
Input voltage:
Since the mains voltage standards of different countries are different, there are many specifications of LED driving voltage. Rated input voltage refers to the specific input voltage of the driver under the specified working conditions. The value and conditions are specified in this specification or by the manufacturer or seller. The input voltage of commonly used LED drivers is AC85-265V, and some manufacturers achieve AC277V.
Output Power:
The specific output power of the driver under the specified working conditions, the value and conditions are specified in this specification or by the manufacturer or seller. LED drivers are generally constant current output, allowing the output voltage to fluctuate within a certain range. Therefore, the output power is a range.
Start Time:
The period of time when the AC power is turned on to 90% of the constant current output rated current (or constant voltage output rated voltage).
Overshoot:
The phenomenon that the output DC voltage or current exceeds a stable value due to a certain amount of transient effect is overshoot. The overshoot amplitude is the maximum transient amplitude of the output current or deviation from the stable value.
Load Regulation:
When all other influences remain unchanged, the relative change in the output current of the constant current driver (or the output voltage of the constant voltage driver) due to the change in load.
Input voltage adjustment rate:
When all other influences remain unchanged, the relative change in the output current of the constant current driver (or the output voltage of the constant voltage driver) due to the change in the input voltage.
Output voltage ripple and noise:
The peak-to-peak value of the AC component included in the output DC voltage.
Input surge current:
When the power is turned on, the maximum instantaneous current value of the AC input circuit.
Creepage distance:
The shortest path measured between two conductive parts along the insulating surface or between the conductive parts and the protective interface of the equipment.
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