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TI公司的UCC28740是绝缘-反激电源控制器,采用光耦器来提高大负载的瞬态响应,恒流(CC)稳压通过初级边稳压(PSR)来实现.电流稳定度±5%,电压稳定度±1%,器件集成了700V起动开关,动态控制工作状态,支持超低待机功耗,主要用在AC/DC电源,电动自行车,服务器PSU,低端洗衣机,烘干机,微波炉,太阳能逆变器等.本文介绍了UCC28740主要特性,框图, 设计案例以及85 - 265VAC输入12V@3A 36W高效适配器参考设计主要特性,电路图和材料清单.

The UCC28740 isolated-flyback power-supply controller provides Constant-Voltage (CV) using an optical coupler to improve transient response to large-load steps. Constant-Current (CC) regulation is accomplished through Primary-side Regulation (PSR) techniques. This device processes information from opto-coupled feedback and an auxiliary flyback winding for precise high-performance control of output voltage and current.

An internal 700-V startup switch, dynamically-controlled operating states, and a tailored modulation profile support ultra-low standby power without sacrificing startup time or output transient response.

Control algorithms in the UCC28740 allow operating efficiencies to meet or exceed applicable standards. The drive output interfaces to a MOSFET power switch. Discontinuous conduction mode (DCM) with valley-switching reduces switching losses. Modulation of switching frequency and primary current-peak amplitude (FM and AM) keeps the conversion efficiency high across the entire load and line ranges.

The controller has a maximum switching frequency of 100 kHz and always maintains control of the peak-primary current in the transformer. Protection features keep primary and secondary component stresses in check. A minimum switching frequency of 170 Hz facilitates the achievement of less than 10-mW no-load power.

UCC28740主要特性:

Less than 10-mW No-Load Power Capability
Opto-Coupled Feedback for CV, and Primary-Side
Regulation (PSR) for CC
Enables ±1% Voltage Regulation and ±5% Current
Regulation Across Line and Load
700-V Startup Switch
100-kHz Maximum Switching Frequency Enables
High-Power-Density Charger Designs
Resonant-Ring Valley-Switching Operation for
Highest Overall Efficiency
Frequency Dithering to Ease EMI Compliance
Clamped Gate-Drive Output for MOSFET
Overvoltage, Low-Line, and Overcurrent
Protection Functions
SOIC-7 Package
UCC28740应用:
AC/DC Power Supply - Dual Analog Controller
E-Bike
Power Supply: AC/DC, Isolated, no PFC,< 90W
Server: PSU
Washing Machine: Low-End
Clothes Washer & Dryer
Microwave Oven
Power Supply: AC/DC, Isolated, w/ PFC,> 90W
Solar Inverters

图1. UCC28740框图

图2. UCC28740简化应用电路图

图3. UCC28740设计案例

85 - 265VAC输入12V@3A 36W高效适配器参考设计

This reference design provides an isolated 12V/36W output from a universal AC input range with over 89% peak efficiency. The UCC24610 synchronous rectifier controller and CSD19531Q5A FET reduce the rectifier loss and provide high efficiency with a minimal increase in cost. The UCC28740 flyback controller uses a combination of peak current modulation and frequency modulation to maintain excellent efficiency at lighter loads and minimize no load power consumption.  The current regulation feature of the UCC28740 provides accurate current limit protection. This compact design consumes a volume of only 2.0" x 2.0" x 0.75".

36W高效适配器参考设计主要特性:

Compact AC/DC adaptor design (2.0" x 2.0" x 0.75")
Synchronous rectification for high efficiency (>89% peak, 88.7% average)
Accurate current limiting
Consumes less than 150mW power at no load to qualify for 4-star EC IPP Mobile device charger rating
Less than 150ms start-up time at full-load

图4.36W高效适配器参考设计外形图

图5.36W高效适配器参考设计电路图
36W高效适配器参考设计材料清单: