Flyback isolated power supply design solves the power supply problem of MCU

　　1. Design of flyback isolated power supply based on SE8510

　　Figure 1 is the schematic diagram of the SE8510 flyback isolated power supply system. The SE8510 is an offline isolated primary-side controlled flyback LED driver control IC. The SE8510 uses a rugged high-voltage isolation process that can withstand an input voltage of up to 450 V and has a wide input voltage range of 8-450V. Therefore, the SE8510 can be directly driven by the main line input voltage, simplifying the transformer design process. It has accurate LED regulation function, PWM regulation control, open-short circuit protection, over-temperature protection and other functions. The overall application design becomes simpler than the previous solution design.

　　Figure 1: SE8510 flyback isolation circuit diagram

　　2. Support PWM to adjust output current and change LED brightness.

　　PWM dimming can be achieved by adding a low-frequency square wave signal to PIN DIM. When the PWM signal is zero, the gate driver is off, and when the PWM signal is high (> 300 mv), the gate driver is enabled. The LED current is proportional to the duty cycle of the PWM wave. In order to reduce frequency interference, it is recommended that the frequency of the PWM control signal be set between 200HZ-500HZ. 　　3. Provide MCU power supply system to solve the power supply problem of MCU control system

　　As shown in Figure 2, the schematic diagram of the traditional control system using MCU output PWM control signal. In the design, the problem of power supply to MCU will be encountered.

　　(1) The AC-DC system itself is designed to output constant current to control the LED brightness. However, the MCU power supply is selected. An independent set of AC-DC power supplies is used as the MCU power supply system. This increases the cost and evolves into designing two independent AC-DC power supplies.

　　(2) Power is provided from the AC-DC LED constant current drive power supply. The auxiliary winding is used for power supply, and the MCU power supply and the AC-DC control IC power supply are taken from the same winding end. However, when the MCU sends a control signal to control the AC-DC control IC and stop the AC-DC system, the auxiliary winding will also lose power, causing the MCU to power off.

　　(3) Putting MCU control in the secondary part of AC-DC, when the AC-DC system is turned off, the output voltage will also drop. Usually, customers design the output to increase the output capacitor, slow down the discharge, and provide it to the MCU. This results in an increase in the size and cost of the output capacitor.

　　Figure 2: Traditional control system using MCU output control signal

　　Figure 3: SE8510 provides MCU power supply, solving the MCU power supply problem when the system is powered off

　　As shown in Figure 3, SE8510 uses a patented power supply system technology. A rugged high-voltage isolation process can withstand an input voltage of 450V and has a wide input voltage range of 8-450V. A high-voltage power supply system from VIN-VDD is added inside the IC. The voltage of VDD is 8V and has a load capacity of 5mA (due to the IC package form of SOP8, the power dissipation is affected). It is enough for the MCU and some PWM generation circuits to work normally (MCU working current 2mA). The VDD voltage is reduced to 5V through a small voltage regulator module, such as 7805, or a voltage regulator composed of triodes. Provided to the MCU or PWM signal generation circuit. For example, the PWM duty cycle adjustable generation circuit generated by NE555. When the MCU sends a PWM low signal, although the SE8510 system is turned off. However, because the VIN-VDD high-voltage module inside the IC works independently, VDD maintains an 8V voltage, so that the MCU will not be powered off and cause the program to restart. And it saves the high cost and large volume brought by the external power supply system circuit.

　　4.Support multiple control modes to make the design more flexible

　　With the diversification of LED lighting, it is more energy-saving and environmentally friendly in certain occasions. Intelligent control has been increasingly favored by consumers. For example, in underground parking lots, human body sensing control is required to achieve full brightness and half brightness control. For example, voice control is used to save electricity in staircases and corridors. There is also remote control, which supports 0-10V, RF and other dimming, and has a wider range of applications.

　　Application diagram of flyback isolation, high PFC, flicker-free, voice control and human body sensing system based on SE8510 design.

　　Figure 4: Application diagram of flyback isolation high PFC, flicker-free, voice control and human body sensing system based on SE8510 design.

　　The dotted box contains the human infrared sensing control circuit and voice control module.

　　In the extended application, add multiple groups or even remote control the color temperature of LED lights, use one group of LED lamp beads with cold white load and another group of LED lamp beads with warm white load. Control the MCU to output different signals to SE8510, control the output of different loads to change the brightness to adjust the LED color temperature.

　　A single MCU control system is used to control multiple LED drive modules to adjust the LED color temperature and brightness.

　　Adopt wireless control module, add a receiving module to control multiple groups of LED drive modules. Adopt wifi, 2.4G radio frequency, infrared remote control, Bluetooth function and other technologies. Change the LED brightness system development combined with mobile phone control. Achieve the higher mission of LED lighting.