原标题：OnSemi NCP4354A 65W空载低功耗离线电源适配器设计方案

　　OnSemi公司的NCP4354A是一款为实现在空载时具有极低功率损耗应用而设计的副边开关电源控制器。该控制器具有空载探测能力和使控制器进入低功率损耗的关断模式。在关断模式期间，原边控制器关断，输出由输出电容来提供能量保持稳压输出由此消除功率消耗。在关断期间，输出电压为释放状态，输出电压被允许减少在可调整的范围内，一旦更多能量被需要，NCP4354A原边控制就会自动启动来提供所需电源。本文首先介绍NCP4354A简介、基本特性、内部框图及应用领域，并给出相应设计方案的设计原理图、元器件列表及PCB元件布局图。

　　The NCP4353/4 is a secondary side SMPS controller designed for use in applications which require extremely low no load power consumption. The device is capable of detecting “no load” conditions and entering the power supply into a low consumption OFF mode. During OFF mode, the primary side controller is turned off and energy is provided by the output capacitors thus eliminating the power consumption required to maintain regulation. During OFF mode, the output voltage relaxes and is allowed to decrease to an adjustable level. Once more energy is required, the NCP4353/4 automatically restarts the primary side controller.The NCP4353/4 controls the primary side controller with an“Active OFF”signal, meaning that it drives optocoupler current during OFF mode to pull−down the FB pin of the primary controller.

　　During normal power supply operation, the NCP4353/4 provides integrated voltage feedback regulation, replacing the need for a shunt regulator. The A versions include a current regulation loop in addition to voltage regulation. Feedback control as well as ON/OFF signal can be provided with only one optocoupler. The NCP4354 includes a LED driver pin implemented with an open drain MOSFET driven by a 1 kHz square wave with a 12.5% duty cycle when primary side is in regulation for indication purpose.

　　The NCP4353 is available in TSOP−6 package while the NCP4354 is available in SOIC−8 package.

　　NCP4354A主要特性：

　　• Operating Input Voltage Range: 2.5 V to 36.0 V

　　• Supply Current < 100 _A

　　• ±0.5% Reference Voltage Accuracy (TJ = 25°C)

　　• Constant Voltage and Constant Current (A versions) Control Loop

　　• Indication LED PWM Modulated Driver (NCP4354x)

　　• Designed for use with NCP1246 Fixed Frequency PWM Controller

　　• This is a Pb−Free and Halide−Free Device

　　NCP4354A应用：

　　• Offline Adapters for Notebooks, Game Stations and Printers

　　• High Power AC−DC Converters for TVs, Set−Top Boxes, Monitors, etc.·POS System

　　图1. NCP4354A内部方框图

　　NCP4354A方案介绍：

　　When designing an offline Ac-Dc power adapter, one key consideration is the power consumption in standby mode. Standby power consumption, also sometimes referred to as vampire power or phantom load, is the power consumed by electronic devices when they are switched off, but still plugged into the wall. It is estimated that standby power accounts for nearly 10% of the energy usage in the average American home. One common contributor to vampire power in the home is notebook adapters. These adapters spend a lot of time left underneath desks with the notebook computer disconnected or powered off. The following design note features the latest techniques for minimizing the standby power consumption of a 65 W notebook adapter.

　　NCP4354A方案主要参数表

　　NCP4354A方案原理图：

　　图2. NCP4354A方案原理图

　　NCP4354A方案材料清单：

　　PCB元件布局图：