OnSemi公司的NCP4354A是一款為實現在空載時具有極低功率損耗應用而設計的副邊開關電源控制器。該控制器具有空載探測能力和使控制器進入低功率損耗的關斷模式。在關斷模式期間，原邊控制器關斷，輸出由輸出電容來提供能量保持穩壓輸出由此消除功率消耗。在關斷期間，輸出電壓為釋放狀態，輸出電壓被允許減少在可調整的范圍內，一旦更多能量被需要，NCP4354A原邊控制就會自動啟動來提供所需電源。本文首先介紹NCP4354A簡介、基本特性、內部框圖及應用領域，并給出相應設計方案的設計原理圖、元器件列表及PCB元件布局圖。
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應用：
• Offline Adapters for Notebooks, Game Stations and Printers
• High Power AC−DC Converters for TVs, Set−Top Boxes, Monitors, etc.·POS System
圖1. NCP4354A內部方框圖
NCP4354A方案介紹：
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方案主要參數表
NCP4354A方案原理圖：
圖2. NCP4354A方案原理圖
NCP4354A方案材料清單：
PCB元件布局圖：
