CNAs an important component of switching power supplies, light-emitting diode switching power supply technology has rapidly developed with the changes in society and demand. After years of use in the market, the stability and safety have been improving. So the demand for technology is getting higher and higher. When studying the design of LED switching power supplies, it is first necessary to understand their classification.
From a general perspective, it can be divided into two categories based on driving mode or power supply mode:
Type 1: Constant current type: 1. The constant current driving circuit is ideal for driving LEDs. 【 LED Switching Power Supply 】 2. The constant current power supply circuit prohibits complete load routing. 3. The output current of the constant current power optocoupler circuit is stable, and the output AC voltage will change within a certain range with the size of the load resistance value. 4. The constant current power supply has a larger load capacity and working voltage value, so please limit the total number of LED applications.
Type 2: Voltage stabilizing tube type: 1. After clarifying the main parameters of the voltage stabilizing power supply circuit, the output is a fixed working voltage, but the output current changes with the adjustment of the load; 2. Although the voltage stabilizing power supply circuit is not afraid of load guidance, it is necessary to prohibit the complete short-circuit fault of the load; 3. The voltage transition after the rectifier can easily harm the chromaticity of LED; 4. It is necessary to add suitable resistors to ensure that the display information chromaticity of each string of LED driven by a stabilized power circuit can be evenly distributed.
According to the design structure of the circuit, it can be divided into six categories.
1. Capacitor voltage reduction mode: This mode is easily affected by power supply voltage fluctuations, and has low efficiency and reliability. Due to the decrease in voltage caused by capacitance, the instantaneous current flowing through the light-emitting diode during flash use is very large due to the effect of charging and discharging, which can easily damage the chip.
2. Resistor blood pressure lowering method: This method has high efficiency and low reliability in removing electricity. The net weight of the appearance design is still emphasized, and the advantage is its small size. Overall, this method is less commonly used in switch mode power supplies.
3. Basic transformer blood pressure lowering method: This type of switch mode power supply is rarely used. Although the appearance design has a small volume, the net weight is still relatively heavy, and the efficiency is low, with low reliability.
4. Voltage reduction method for electronic transformers: The disadvantages of this method are low power efficiency, limited voltage range, large ripple interference, and limited use in the market for this type of power supply product.
5. RCC voltage reduction method switch mode power supply: The advantage of this method is high efficiency and wide application. The disadvantage of LED switch power supply is that the vibration frequency of the control mode is discontinuous, the switching frequency is difficult to control, the adaptability to abnormal loads is poor, and the load voltage ripple coefficient is relatively large, which is not recommended for use.
6. PWM control mode switching power supply: It is recommended to design and use this mode power supply. It consists of four parts, namely input rectification and filtering part, output rectification and filtering part, PWM voltage stabilization control part, and switch energy conversion part. The basic working principle of P is that when the input voltage, internal parameters, and external loads change, the control circuit provides closed-loop feedback through the difference between the controlled signal and the reference signal, adjusts the pulse width of the main circuit switching device, and stabilizes the output voltage or current of the switching power supply (i.e., the corresponding stable voltage or constant current power supply). Its advantages are high efficiency, stable output voltage and current. This type of power supply design has complete protection measures.
