25W高效（>90%）高功率因素（>0.97）非隔离Buck-Boost型T10灯管LED驱动参考设计报告

　　1 Introduction

　　This document describes a non-isolated， power factor corrected， low THD， high-efficiency

　　LED driver designed to drive a 144 V LED string at 180 mA from an input voltage range

　　of 90 VAC to 265 VAC.

　　The LYTSwitch-4 has been developed to cost effectively implement a single-stage power

　　factor corrected LED driver combined with primary-side constant-current control. The

　　LYTSwitch-4 controller is optimized for LED driver applications and requires minimal

　　external parts. It provides control of output current without the use of an optocoupler.

　　The LYTSwitch-4 monolithically combines the 725 V power MOSFET and controller. The

　　controller consists of an oscillator， PWM， 6 V regulator， over-temperature protection，

　　frequency jittering， cycle-by-cycle current limit and other protection features plus a charge

　　controller for output CC （constant current） control.

　　The LYTSwitch-4 provides a sophisticated range of protection features including autorestart for control loop open/short faults and output short-circuit conditions. The accurate

　　hysteretic thermal shutdown ensures safe PCB temperatures under all conditions.

　　The non-isolated power factor corrected buck-boost design presented in this report

　　shows how LYTSwitch-4 dramatically simplifies off-line， high-efficiency， power factor

　　corrected LED driver design and enables an EN 61000-3-2 Class C compliant

　　implementation of a very high efficiency， high output voltage LED driver.