原标题：On Semi NCP1219通用AC输入非绝缘6W电表降压电源方案

　　On Semi 公司的NCP1219是有动态自偏压电源的PWM控制器,具有极好的待机功耗,采用带斜率补偿的固定频率电流模式运作,频率在65kHz和100kHz选择,不需要辅助绕组,峰值源/沉电流驱动能力500mA/800mA,主要用在笔记本电脑,LCD监视器的AC/DC适配器,离线电池充电器,消费类电子如STB,DVD,DVDR电源.本文介绍了NCP1219主要特性,功能方框图,应用电路图以及通用AC输入非绝缘6W电表降压电源参考设计主要特性与指标,电路图和材料清单.

　　NCP1219: PWM Controller Featuring Dynamic Self Supply

　　The NCP1219 represents a new, pin to pin compatible, generation of the successful 7−pin current mode NCP12XX product series. The controller allows for excellent standby power consumption by use of its adjustable skip mode and integrated high voltage startup FET. Internal frequency jittering, ramp compensation, timer−based fault detection and a latch input make this controller an excellent candidate for converters where ruggedness and component cost are the key constraints.

　　The Dynamic Self Supply (DSS) drastically simplifies the transformer design in avoiding the use of an auxiliary winding to supply the NCP1219. This feature is particularly useful in applications where the output voltage varies during operation (e.g. battery chargers). Due to its high voltage technology, the IC can be directly connected to the high voltage dc rail.

　　NCP1219主要特性:

　　• Fixed−Frequency Current−Mode Operation with Ramp Compensation (65 kHz and 100 kHz Options)

　　• Dynamic Self Supply Eliminates the Need for an Auxiliary Winding

　　• Timer−Based Fault Protection for Improved Overload Detection

　　• Cycle Skip Reduces Input Power in Standby Mode

　　• Latch and Auto−Recovery Overload Protection Options

　　• Internal High Voltage Startup Circuit

　　• Accurate Current Limit Detector (±5%)

　　• Adjustable Skip Level

　　• Latch Input for Easy Implementation of Overvoltage and Overtemperature Protection

　　• Frequency Modulation for Softened EMI Signature

　　• 500 mA/800 mA Peak Source/Sink Current Drive Capability

　　• Pin to Pin Compatible with the Existing NCP12XX Series

　　• These Devices are Pb−Free and Halogen Free/BFR Free*

　　NCP1219典型应用:

　　• AC−DC Adapters for Notebooks, LCD Monitors

　　• Offline Battery Chargers

　　• Consumer Electronic Appliances STB, DVD, DVDR

　　图1.NCP1219功能方框图

　　图2.NCP1219应用电路图

　　通用AC输入非绝缘6W电表降压电源参考设计

　　This design note describes a simple, low power, off-line, extended universal AC input buck power supply intended for powering utility electric meters or similar industrial equipment or white goods where isolation from the AC mains is not required and low cost and circuit simplicity is essential.

　　The featured power supply is a simple buck regulator topology utilizing ON Semiconductor’s NCP1219B current mode PWM controller riving an external Dpak MOSFET (Q1). The controller circuitry is ground referenced to the freewheel diode’s cathode terminal which is a switched node. This allows for simple halfwave input rectification and a common AC input to dc output node. Because the NCP1219 controller and its associated circuitry are at a switched node, optocoupler feedback from the NCP431 output sensing amplifier is utilized to avoid regulation inaccuracies typically caused by charge pump and/or bootstrap type sensing schemes. Diode D4 also powers the control circuitry from the output voltage once the converter has started.

　　The half-wave input rectifier section utilizes a pi-network, split bulk capacitor scheme which provides for both high input transient protection (with optional TVS1) and effective conducted EMI attenuation. The choice of the total bulk capacitance can be selected for the desired output hold-up time during line cycle outages or extreme brownout conditions. Hold-up time along with efficiency and output ripple plots are shown below.

　　通用AC输入非绝缘6W电表降压电源主要指标:

　　通用AC输入非绝缘6W电表降压电源主要特性:

　　Extended universal AC input range (60 – 300 Vac) with up to 10 watts peak output.

　　Bulk pi-network filter for conducted EMI attenuation and input transient protection.

　　AC input to dc output common node.

　　Inherent over-current protection and optional Z1 over-voltage protection clamp.

　　Simple, low cost circuitry with off-the-shelf output inductor (L2).

　　图3.采用NCP1219B65的6W离线电源电路图

　　通用AC输入非绝缘6W电表降压电源材料清单(BOM):