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ACF PWM Controller Meets Modern AC-DC Power Conversion Needs

[Introduction]In high-density AC-DC power conversion, the flyback topology is traditionally used, but there has been a bottleneck in efficiency and power density. The new type of active clamp flyback (ACF) topology , improves performance and reduces power consumption while minimizing the size and weight of the power converter. This article will give you an introduction to the characteristics of ACF topology and the ACF PWM controller solution introduced by onsemi.

ACF PWM Controller Meets Modern AC-DC Power Conversion Needs

ACF topology provides smaller size and higher energy efficiency

Modern power supply applications pursue more compact size and higher efficiency, which makes power supply designers more and more inclined to choose high-frequency applications. Switching power supply using high-frequency operation can reduce the size of the transformer, thereby increasing the power density of the power supply. With the advancement of high-voltage FETs and the emergence of wide-bandgap semiconductor devices such as gallium nitride (GaN)/silicon carbide (SiC), new ACF topologies are playing a role in high-density power conversion applications.

ACF topology utilizes energy stored in parasitic components to achieve zero voltage switching (ZVS) rather than dissipating it in snubber circuits. Active clamp operation produces waveforms free of parasitic spikes, resulting in better electromagnetic interference (EMI) performance than other conventional techniques. While the classic flyback topology with RCD snubbers has reached its limits in terms of efficiency and power density, the ACF topology solves the efficiency challenge while reducing EMI emissions.

ACF PWM Controller Meets Modern AC-DC Power Conversion Needs

Energy Efficient AC-DC Active Clamp Flyback PWM Controller

The NCP1568 from ON Semiconductor is a highly integrated AC-DC PWM controller for implementing an Active Clamp Flyback (ACF) topology. The NCP1568 uses a proprietary frequency conversion algorithm to achieve ZVS of the MOSFET under various line and load conditions. The ZVS function enables high frequency operation, increasing the power density of the power converter while achieving high energy efficiency.

ACF operation simplifies EMI filter design to avoid interfering with other sensitive circuits in the system. The NCP1568 integrates high-voltage start-up circuitry, powerful low-side drivers, and 5V logic-level drivers for active clamp FETs, including SJ FETs and GaN FETs.

The NCP1568 also features multi-mode operation and conversion from ACF mode to discontinuous conduction mode (DCM) to meet regulatory requirements around the world. The NCP1568 further enables skipping in standby mode, resulting in excellent standby power consumption. NCP1568 is a programmable control scheme that supports mute hopping, programmable frequency, proprietary adaptive ZVS to allow high frequency operation while reducing EMI, multi-mode operation to improve light-load efficiency, flexible control scheme and user-programmable functions Combined, allows the use of the NCP1568 with Superjunction MOSFET (Silicon) and Gallium Nitride (GaN) FETs with minimal frequency clamping and silent jumps to eliminate audible noise, programmable frequencies from 100 kHz to 1 MHz operation below.

ACF PWM Controller Meets Modern AC-DC Power Conversion Needs

For applications with high power density requirements

NCP1568 supports built-in adaptive dead time for primary and active clamp FETs, peak current mode control with built-in slope compensation option, flexible control scheme and programmability, allows configuration with external silicon or GaN FETs, customer programmable Option transitions to DCM, integrated frequency foldback with minimum frequency clamp for maximum performance in standby mode, less than 30 mW standby power, integrated 700 V high voltage and startup circuitry, supports AC line brownout detection.

The NCP1568 features low-side 0.85 A/1.5 A source/sink drivers, and 65 mA/150 mA active clamp driver output oscillators, an internal soft-start timer with 4 options. In terms of protection functions, it has a dedicated FLT pin compatible with thermistors, as well as adjustable over-power protection (OPP), options to support automatic recovery and lockout of various faults and an internal thermal shutdown function.

The NCP1568 is suitable for a variety of applications, including AC-DC adapters, industrial, telecom, lighting and other applications that require high power density, suitable for AC-DC power conversion, as well as USB power delivery (Power Delivery) and Qualcomm (Qualcomm) For Quick Charge applications, common end products include high-density notebook and mobile adapters, USB Type-C power supplies, server auxiliary power supplies, and industrial power supplies.

ACF PWM Controller Meets Modern AC-DC Power Conversion Needs

Multiple evaluation boards to speed development of multiple applications

ON Semiconductor has also launched a number of evaluation boards for different applications, including the NCP1568DC48WGEVB is a 48 W, 120 V to 400 V wide range DC input constant voltage power supply, suitable for server auxiliary power supply and other needs low height, high efficiency and high Power Density for DC Input Applications. The NCP1568DC48WGEVB uses an ACF topology, with ON Semiconductor’s NCP1568 ACF controller, NCP51530A half-bridge driver, NCP4306 synchronous rectifier controller, and secondary NTMFS6B03 synchronous MOSFET, which can achieve over 94% efficiency at full load.

NCP1568PD60WGEVB is NCP1568 USB-PD 60W evaluation board, with NCP1568 AC-DC PWM controller, designed to realize ACF topology, this evaluation board can be used for evaluation of 60W USB PD application. Another evaluation board, the STR-ACF-12V100WPSU-GEVB, provides an easy-to-use evaluation board for the NCP1568 100W output AC-to-DC conversion in the Strata development environment for industrial use and general-purpose power supplies.


ACF topology has become the main design architecture for high-density power conversion applications, which can meet the requirements of high energy efficiency, low EMI, and compact size. It can be widely used in power converters using wide-bandgap semiconductor devices such as GaN/SiC. Market applications Great potential for development. ON Semiconductor’s NCP1568 AC-DC ACF PWM controller, with high integration and complete functionality, will be the best partner for developing these products.

The Links:   HSD150SX84-A 1DI50MA-050