COURSES TAUGHT BY PROF. VALDENILTON: Basic Electronics Course Level 1 and 2 Online (100% in VIDEO) https://go.hotmart.com/S90922297H?dp=1 Digital LCD/LED TV Repair Course (100% in PDF) https://technologycursos.wixsite.com/... SHARE THIS VIDEO WITH THOSE YOU LOVE: • How the PFC circuit of a power supply works... PFC stands for Power Factor Correction. From 100W of power onwards, a switching power supply requires a circuit that corrects its power factor, improving its energy efficiency. In this series of three videos, you will learn how to analyze how the PFC circuit of a switching power supply works, from standby to full operation. The PFC circuit has several functions in a switching power supply. In addition to correcting the power factor, it also contributes to improving the quality of the energy that will be produced by the switching power supply. Another important function performed by the PFC circuit is to reduce the inrush current that will circulate when the power supply is energized for the first time, thus ensuring the longevity of the diode bridge and the filter capacitor. The focus of this series of videos is to show how the PFC circuit of a switching power supply works. The functions it performs for the switching power supply will be analyzed in more detail in future classes. PFC CIRCUIT CONSTITUTION The PFC circuit is made up of five main elements, namely: 1) PWM oscillator circuit; 2) Power switching MOSFET; 3) Inductor; 4) Rectifier diode; 5) Bypass diode Each component described above has a very defined function in the process of correcting the power factor as well as improving the quality of energy delivered to the circuits of a Digital TV. STANDBY OPERATION: When the power cable of the switched-mode power supply is connected to the electrical outlet, the alternating voltage enters the diode bridge (BR). At the output of the diode bridge, we have a pulsating direct voltage. This voltage tends to charge the filter capacitor(s) and at this moment the load current is very high. In this case, the bypass diode comes into play, which divides the load current of the filter capacitor with the rectifier diode of the PFC circuit, greatly minimizing the inrush current. If the power button on the TV is not pressed, it will remain in the standby state. When the TV is in standby, the PFC circuit is inoperative and in the filter capacitor we will have a stored voltage of approximately 310V (if the TV is connected to a 220V network). In this case, the PFC circuit coil does not react and there is no creation of a magnetic field between its terminals because the MOSFET transistor is in the cut-off state. STARTING THE PFC CIRCUIT: When the power button is pressed, the soft start capacitor starts charging and when it reaches 12V, the internal comparator releases the PWM oscillator IC. When it starts operating, the PWM oscillator IC releases pulses to trigger the power switching MOSFET, which, when it enters saturation, allows a current to flow through the PFC circuit coil. At this moment, the anode of the PFC circuit rectifier diode is reverse biased and it enters the cut-off state. During the time that the MOSFET is triggered by the PWM pulses, the current that passes through the coil increases, inducing a growing magnetic field in its auxiliary winding. This magnetic field that grows in the auxiliary winding will be applied, via resistor, to the ZCD pin of the PWM oscillator IC and will be monitored by an internal comparator. When the voltage of this magnetic field of the auxiliary winding reaches 1.5 V, the internal comparator generates a command at its output that turns off the internal flip-flop, preventing the production of PWM pulses. At this moment, the MOSFET transistor goes into cutoff, interrupting the current flowing through the PFC coil, allowing the EMF to appear between its terminals. The appearance of the EMF in the PFC coil inverts the polarity of the coil terminals, allowing the rectifier diode to conduct, which, when it starts conducting, charges the filter capacitor with approximately 90 V, which will be added to the 310 V already present in the capacitor, totaling 400 V at the output of the switched-mode power supply. As the rectifier diode consumes the magnetic field of the coil, it decreases, and the same happens in its auxiliary winding. When the auxiliary winding voltage reaches 1.4V, the internal comparator polarizes the flip flop again and it starts working, generating PWM pulses at the output of the PWM oscillator IC that polarizes the gate of the power switching MOSFET again, allowing a current to circulate again through the coil, repeating a new operating cycle. Hello, I am Prof. Valdenilton, Technical Coordinator of the Electronics courses taught by Technology Cursos. INFORMATION: Business contact: [email protected] Whatsapp Center: (82) 9 8706-9200