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/... Transformer Winding Course (100% in PDF) https://hotm.art/Curso-de-enrolamento... COURSES TAUGHT BY OTHER TEACHERS: Basic Electronics Course (with a focus on repair) https://hotm.art/Curso-de-eletronica-... Basic Electronics Course (with a general focus) https://hotm.art/Curso-de-eletronica-... Cell Phone Repair Course (version 5.0) https://hotm.art/Conserto-de-celular-top Cell Phone Repair Course Notebook Motherboard https://hotm.art/Conserto-de-placa-ma... Voltage Inverter Manufacturing and Repair Course https://hotm.art/Aprenda-a-fazer-inve... Photovoltaic Solar Energy Course https://hotm.art/Curso-energia-solar-... Complete Digital Marketing Course (from scratch) https://hotm.art/Curso-de-Marketing-D... VIDEOS TO COMPLEMENT THE STUDY • Analysis of the Power Supply Line Filter... SHARE THIS VIDEO WITH FRIENDS: • Starting and Feedback Circuit. ... SUBSCRIBE TO OUR CHANNEL BY CLICKING THE LINK BELOW: / @technologycursosoficial One of the most important circuits of the switching power supply (perhaps the most important) is the starting and feedback circuit. In today's class, you will learn how the start and feedback circuit keeps the switching power supply oscillating, maintaining the output voltages. When the network cable is connected to the outlet, no voltage is available at the power supply output, because the PWM Oscillator IC is turned off. To enable the PWM oscillator IC to operate, the manufacturer uses a portion of the power supply voltage to a resistor in series with an electrolytic capacitor, with the intention of generating a ramp that, when reaching a satisfactory voltage between the capacitor plates (in the case of the IC shown in the video, 16V), allows the UVLO protection to release the operation of its internal circuits. This resistor is known as the start resistor, precisely because it is the first to supply voltage to the PWM oscillator IC. Depending on the power supply, there may be several start resistors. When the PWM oscillator IC starts operating, it tends to discharge the electrolytic capacitor and if it reaches the level of 7.5V for the IC analyzed in the video, it will be turned off by the UVLO protection. If the PWM oscillator IC is turned off by the UVLO protection, the source voltage drops to zero and since the starting circuit formed by the resistor and the capacitor continues to receive a portion of the AC voltage, the capacitor reaches 16V again and the source turns on again, turning off immediately after due to the voltage consumption of the capacitor by the internal circuits of the PWM IC. So what can be done to prevent the PWM oscillator IC from consuming the capacitor and it reaching the level that triggers the UVLO protection? The manufacturer adds a feedback circuit on this same pin formed by a secondary winding of the chopper transformer and a rectifier diode. Therefore, when the switching MOSFET of the switched-mode power supply starts operating for the first time through the PWM pulses generated by the PWM oscillator IC, the magnetic field produced in the secondary coil is rectified by the diode, keeping the capacitor charged with 16V, allowing the UVLO protection to maintain the operation of the internal oscillator of the PWM IC. The feedback and control circuit can be tested using either a digital multimeter or a digital oscilloscope. Conclusion: I hope that by the end of this lesson, you will be able to understand how the VCC start and feedback circuit keeps the switching power supply fully operational. Hello, I am Professor Valdenilton, Technical Coordinator of the Electronics courses taught by Technology Cursos. I love transforming people's lives through teaching. My goal is to teach people like you how to repair the electronic equipment they love, helping in every way possible. INFORMATION: Our Website: https://technologycursos.wix.com/tech... Business Contact: [email protected] Whatsapp Center: (82) 9 8706-9200 (Only by messages or audio)