As an important part of switching power supply, led switching power supply technology has developed rapidly with the changes of society and demand. It has been used in the market for many years, and its stability and security are getting better and better. Therefore, the requirements for technology are getting higher and higher. When studying the design of LED switching power supply, we first need to understand its classification. Generally speaking, according to the driving mode or power supply mode, it can be divided into two categories:
Class I: constant current type: 1. Constant current drive circuit is ideal for driving LED. [led switching power supply] 2. The constant current power supply circuit prohibits the load from leading the way completely 3. The output current of the constant current power supply optocoupler circuit is stable, and the output AC voltage will change in a certain range with the size of the load resistance 4. The constant current power supply has a large amount of current and working voltage, so please limit the total number of LED applications. Class II: stabilized voltage tube type: 1. After various main parameters of the stabilized voltage supply circuit are defined, the output is the fixed working voltage, but the output current changes with the load adjustment; 2. Although the regulated power supply circuit is not afraid of load leading, it is prohibited to completely short-circuit the load; 3. The change of working voltage after rectifier will easily endanger the chromaticity of LED; 4. Be sure to add a suitable resistor so that the display information chromaticity of each string of LED driven by the regulated power supply circuit can be symmetrical. According to the design structure of the circuit, it can be divided into six categories.
1. capacitor step-down mode: this mode is easily affected by power supply voltage fluctuation and has low efficiency and reliability. Because the capacitor reduces the voltage, the instantaneous current flowing through the LED is very large due to the charge and discharge when the flash is used, which is easy to damage the chip. 2. method of reducing blood pressure by resistor: this method has low efficiency and credibility. The net weight of the appearance design is still focused on. The advantage is that the size is small. In general, this method is rarely used in switching power supply. 3. basic transformer blood pressure reduction method: this kind of switching power supply is rarely used. Although the design volume is small, the net weight is still heavy, the efficiency is low, and the credibility is not high. 4. electronic transformer step-down mode: the disadvantage of this mode is that the power efficiency is low, the voltage range is not wide, the ripple interference is large, and it is rarely used in this type of power products in the market. 5. RCC step-down switching power supply: this mode has the advantages of high efficiency and wide application. [led switching power supply] the disadvantages are that the vibration frequency of the control mode is discontinuous, the switching frequency is difficult to control, the adaptability of abnormal load is poor, and the load voltage ripple coefficient is relatively large, so it is not recommended. 6.pwm control mode switching power supply: this mode power supply is recommended for design. It consists of four parts: input rectifier and filter part, output rectifier and filter part, PWM regulator control part and switching energy conversion part. P its basic working principle is that when the input voltage, internal parameters and external load change, the control circuit carries out closed-loop feedback through the difference between the controlled signal and the reference signal, and adjusts the pulse width of the switching device of the main circuit to stabilize the output voltage or current of the switching power supply (i.e. the corresponding regulated power supply or constant current power supply). The utility model has the advantages of high efficiency, stable output voltage and current. This design type of power supply has complete protection measures. The above shows the classification of LED power transformer. [led switching power supply] can generally be classified according to drive, power supply mode and design structure. Compared with the classification of power transformer, LED power transformer is simpler. When designing the power supply, please refer to the above classification.
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