基于iW3620的40W AC-DC LED驱动方案
iW3620是iWatt公司的高性能AC/DC离线LED驱动器，器件在高负载条件下工作在准谐振模式，以得到高的效率和各种内置的保护特性，降低EMI，工作频率高达130kHz，通用输入电压85 Vac到 264 Vac，可驱动40W 的LED照明。本文介绍了iW3620主要特性以及典型应用电路。
iW3620：Digital PWM Constant Current Controller for AC/DC LED Driver
The iW3620 is a high performance AC/DC offline LED driver which uses digital control technology to build peak current mode PWM flyback power supplies. The device operates in quasi-resonant mode at heavy load to provide high efficiency along with a number of key built-in protecTIon features while minimizing the external component count, simplifying EMI design and lowering the total bill of material cost. The iW3620 removes the need for secondary feedback circuitry while achieving excellent line and load regulaTIon. It also eliminates the need for loop compensaTIon components while maintaining stability over all operaTIng conditions. Pulse-by-pulse waveform analysis allows for a loop response that is much faster than traditional solutions, resulting in improved dynamic load response. The built-in current limit function enables optimized transformer design in universal off-line applications over a wide input voltage range.
iW3620主要特性：
Primary-side feedback eliminates opto-isolators and simplifies design
Quasi-resonant operation for highest overall efficiency and low EMI
Up to 130 kHz switching frequency enables small size
Very tight LED constant current regulation
Built-in output constant-current control with primary-side feedback for LED driver.
Low start-up current (10 μA typical)
Built-in soft start
Built-in short circuit protection and output overvoltage protection
Current sense resistor short protection
Over-temperature Protection
Open circuit protection
Universal input range from 85 Vac to 264 Vac
Single-fault protection
Small input bulk capacitor
Long MTBF
High efficiency
iW3620应用：
Solid State LED lighting for incandescent, halogen, and fluorescent tube replacement 
图1 iW3620典型应用电路
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