Thursday, June 13, 2024

Reference Design Of Flyback Converter For Set-Top Boxes

The design offers a 40W power supply for Set-Top boxes, supporting wide input voltages and four outputs with high efficiency, low standby power, and cost-effectiveness.

flyback converter

Including flyback converters in Set-Top box designs is a pivotal engineering choice, addressing the crucial need for efficient power conversion and electrical isolation within such devices. These converters play an essential role in transforming high AC mains voltage to the lower, varied DC voltages required by the diverse components of a Set-Top box, from its processing units to its display interfaces. Beyond mere voltage conversion, flyback converters ensure the safety and operational integrity of Set-Top boxes by providing galvanic isolation, thereby protecting sensitive electronics from potential line noise, surges, or electrical faults. Their ability to offer multiple outputs from a single transformer also aligns perfectly with the compact, cost-effective, and multi-functional nature of contemporary Set-Top boxes, underscoring their significance in the efficient, reliable, and safe operation of these ubiquitous consumer electronic devices.

A 40W Switch Mode Power Supply reference design from STMicroelectronics is tailored explicitly for Set-Top box usage. This design can handle a broad spectrum of input voltages (90 to 265Vrms) and provides four distinct outputs. It utilizes the advanced L6668 controller, operating in a fixed frequency PWM current mode. Notable for its high efficiency and reduced power consumption in standby mode, this design also benefits from a low number of necessary components and a cost-effective overall solution. These attributes make it a perfect option for powering digital consumer devices, aligning with global standby regulations.

The Switch Mode Power Supply (SMPS) showcases an extensive range of input and output specifications tailored to various applications. It accepts an input voltage range of 90 – 264 Vrms and operates within a frequency range of 45-66Hz. This broad operational spectrum is complemented by its efficient energy use in standby mode, where it consumes less than 1W with a residual load of 5V at 50mA. The design is further enhanced with short circuit protection across all outputs, which automatically restarts after a short is cleared, ensuring reliability and safety. The PCB is crafted from a single-sided 70um (2-Oz) CEM-1 material, measuring 150 x 75mm, and complies with EN60065 safety standards, maintaining a minimum creepage and clearance distance of 6.4mm.

Electromagnetic interference compliance is achieved through adherence to EN50022-Class B standards, reflecting the power supply’s design for minimal environmental impact. The versatility of the SMPS is evident in its output capabilities, designed to efficiently power digital circuitry, analogue peripherals, HDD, and 5V circuitry, as well as specialized applications like HDD, SCART, and LNBP21 for satellite STBs. With an average power output of 40W and a peak of 51W, the power supply is engineered to meet the demanding requirements of various electronic devices, illustrating its efficiency and robustness in handling diverse operational demands.

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STMicroelectronics has tested this reference design. It comes with a Bill of Material (BOM), schematics, etc. You can find additional data about the reference design on the company’s website. To read more about this reference design, click here.

Nidhi Agarwal
Nidhi Agarwal
Nidhi Agarwal is a journalist at EFY. She is an Electronics and Communication Engineer with over five years of academic experience. Her expertise lies in working with development boards and IoT cloud. She enjoys writing as it enables her to share her knowledge and insights related to electronics, with like-minded techies.


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