A: LED driver switching power supply introduction

by:MOSO     2019-12-15
The professional name is too complicated to say. I summarized the LED driver that can output different voltages at the same time and has a good voltage regulation. ?The main function is to output a constant current and a stable single voltage for the LED lamp beads. Two: LED driver switching power supply circuit structure The following is the schematic diagram ? ?I summarized the most basic 5 parts of the constant current switching power supply Three: Explanation of the role of digital labels corresponding to electronic components ? 1. Input circuit anti-surge and lightning protection and short circuit protection; This is a varistor connected to the fuse. When the transient surge voltage occurs and exceeds the breakdown voltage of the varistor, the resistance of the varistor becomes lower to about a few ohms, which promotes the fuse to overcurrent and fuse, thereby protecting it. And disconnect the circuit. 2. Electromagnetic interference LC filter (also called EMI) Yellow safety capacitors (also known as X2 capacitors, metalized polypropylene film anti-interference film capacitors) and filter inductors constitute a π-type filter network, which mainly suppresses electromagnetic noise and clutter signals of the input power supply to prevent interference to the power supply At the same time, it also prevents the high frequency clutter generated by the power supply from interfering with the power grid. 3.Input rectification Change the positive and negative alternating current into unidirectional changing direct current. The picture above uses the rectifier bridge vertebra 4.High voltage filter circuit Smooth the changed voltage waveform into a DC voltage waveform with less fluctuation. Generally used electrolytic capacitors, the above picture is a unipolar PFC circuit, using CBB polypropylene capacitors 5, RCD spike pulse absorption circuit At the moment when the high-speed switch of the field-effect transistor (MOS tube) is turned off, resonance occurs between the primary inductance of the transformer and the distributed capacitance, and the back-EMF generated by the primary inductance also generates a high spike, which may break down the effect tube switch. tube. The role of the RCD spike absorbing circuit is to prevent and suppress higher spike pulses to protect the safety of the effect switch. 6. Field effect tube (MOS tube) The LED driver switching power supply controls the field effect tube (MOS tube) to be turned on and off at a high speed through a control chip, and converts DC power into high frequency AC power to the transformer for voltage transformation, thereby generating the required safe isolation voltage. The maximum reverse voltage that a field-effect transistor (MOS tube) as a switching tube withstands is twice the working voltage of the circuit, and the operating frequency is between 20-200kHz. At 220V input voltage, the withstand voltage of the switch is generally greater than 650V. 7. Transformer: The conversion process is: electricity-magnetism-electricity stores energy to produce the required output voltage, and the primary (primary side) and secondary (secondary side) are isolated. The electrical gap between the two stages of the transformer is ≥8.0mm. The design of the winding and shield of the transformer has a great impact on the radiated interference in electromagnetic compatibility EMC. 8.Photoelectric optocoupler The main role in the LED driver switching power supply circuit is to perform photoelectric transmission of the control signal of the measured voltage between the primary and secondary of the switching power supply transformer, and to realize the signal feedback of optical isolation from the primary PWM control chip. High voltage and low voltage are not directly connected, which realizes safe isolation and protects personal safety. It is an important control device in safety certification, and it must be selected with a safety certification when used. In practical applications, the general type of photoelectric optocoupler is PC817. 9.Y2 capacitor Generally connected to high voltage ground and low voltage ground. The role is to suppress high-frequency interference, and the Y2 capacitor is helpful to improve the radiation interference in electromagnetic compatibility EMC. 10.Output rectifier diode Change the positive and negative alternating current into unidirectional changing direct current. 11.Low voltage filter circuit Smooth the changed voltage waveform into a DC voltage waveform with less fluctuation. 12. The sampling resistor feeds back the changes in output voltage and current to the control circuit for identification and processing in the form of voltage drop. Select the resistance value according to the size of the constant current. 13.LED driver switching power supply control chip
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