Introduction

USB Power Delivery (USB PD) is a standardized fast-charging technology that enables bidirectional power transmission through a USB-C port. It supports a wide range of devices, including smartphones, tablets, and laptops. The latest USB PD 3.1 specification allows for power outputs of up to 240W, with a maximum output voltage of 48V when using a 5A charging cable. This increase in voltage and power poses challenges for traditional Flyback converter designs, as component voltage stress becomes a significant issue. Additionally, LLC resonant converters used in USB PD applications require an extra step-down circuit for voltage regulation, increasing system cost.

The asymmetric half-bridge Flyback topology (AHB Flyback) offers a viable alternative, providing zero voltage switching (ZVS), high efficiency, and high power density. This topology supports wide voltage outputs, making it well-suited for USB PD 3.1 applications.

Leadtrend LD5780

The LD5780 is a high-performance current-mode PWM controller designed specifically for high-frequency asymmetric half-bridge Flyback converters. It is ideal for high-efficiency power supply systems. The chip features an integrated 700V high-voltage startup circuit and supports X-capacitor discharge functionality. It also includes an internal boost circuit and low-dropout linear regulator, supplying stable power to external MOSFET/GaN HEMT drivers and PFC controllers, simplifying peripheral circuit design.

With adaptive ZVS modulation technology, the LD5780 automatically tracks and achieves zero-voltage switching, reducing switching losses. This feature is particularly beneficial under light to medium load conditions, where efficiency improvements are most noticeable. The controller also employs grouped pulse-width modulation (PWM) techniques, allowing a hybrid CRM+DCM operation mode under lighter loads, further minimizing switching losses.

To optimize system efficiency under light loads, the LD5780 offers an integrated PFC control interface that dynamically adjusts PFC output. This enhances power factor correction, reducing energy waste. The driver section provides a ±10mA/-25mA TTL-compatible MSW/ASW signal output, supporting flexible high-side and low-side driving configurations compatible with various power device topologies.

From an integration standpoint, the LD5780 includes a built-in boost circuit, addressing voltage endurance and power consumption challenges in USB PD 3.1 wide-voltage applications (5V-48V). Additionally, its X-capacitor discharge functionality minimizes standby power consumption. The LD5780 incorporates comprehensive multi-protection features, including input/output overvoltage protection, overcurrent protection, overload protection, internal/external over-temperature protection, and AC input undervoltage/overvoltage detection.

Packaged in a compact SOP-16, the LD5780 is well-suited for AC/DC adapters, battery chargers, open-frame switching power supplies, and high-power adapters.

Leadtrend has developed a full power delivery solution utilizing the LD5780 in combination with its PFC controller (LD7593DA), synchronous rectifier controller (LD8529U), and USB PD protocol controller (LD6618). This comprehensive solution enables highly efficient 240W USB PD applications.

Using an asymmetric half-bridge Flyback topology, combined with GaN power devices and high-frequency magnetic components, this design supports a wide output voltage range (5V to 48V) under the USB PD 3.1 protocol, with a maximum 5A output current. Efficiency tests reveal that the system achieves over 93% efficiency under typical input conditions, meeting the CoC Tier 2 energy efficiency standard. Standby power consumption remains below 75mW at 230V input, while output voltage fluctuation remains minimal under dynamic load conditions, highlighting its exceptional performance.

Summary

With its advanced design and innovative features, the LD5780 delivers a powerful and efficient solution that meets the stringent demands of USB PD 3.1 applications. Its asymmetric half-bridge Flyback topology allows for higher conversion efficiency and compact system designs, particularly beneficial for wide voltage output requirements. The adaptive ZVS modulation further enhances efficiency by minimizing switching losses under light to medium loads, a crucial factor in modern fast-charging technologies.

The LD5780’s high level of integration simplifies circuit design while ensuring system reliability and stability. Its comprehensive protection mechanisms enhance the safety of power supply systems across various operating conditions. With applications spanning AC/DC adapters, battery chargers, and high-power adapters, the LD5780 stands out as a key component in next-generation power solutions.

From a professional perspective, the LD5780 not only meets the high-power output requirements of USB PD 3.1 but also optimizes energy efficiency through precise PFC control and low standby power consumption. By excelling in power conversion efficiency, load regulation, and energy efficiency standards, the LD5780 proves to be an ideal choice for high-power adapter applications.