allegromicro 公司的str-x6757是离线准谐振开关稳压器,具有比通常的pwm解决方案更低的emi噪音特性,特别是频率大于2mhz时. str-x6757采用to-3p封装,包含控制器芯片(mic)和650 vdss/0.62ω rds(on)的mosfet,230vac输入时输出功率高达320w,通用电压输入达到165w,主要用于stb, lcd pc监视器,lcd tv,打印机和扫描仪.本文介绍str-x6757主要特性和优势, 方框图和典型应用电路.
str-x6757: off-line quasi-resonant switching regulators
the str-x6757 is a quasi-resonant topology ic designed for smps applications. it shows lower emi noise characteristics than conventional pwm solutions, especially at greater than 2 mhz. it also provides a soft-switching mode to turn on the internal mosfet at close to zero voltage (vds bottom point) by use of the resonant characteristic of primary inductance and a resonant capacitor.
the package is a fully molded to-3p, which contains the controller chip (mic) and mosfet, enabling output power up to 320 w at 230 vac and 165 w at universal input. the bottom-skip mode skips the first bottom of vds and turns on the mosfet at the second bottom point, to minimize an increase of operating frequency at light output load, improving systemlevel efficiency over the entire load range.
there are two standby modes available to reduce the input power under very light load conditions. the first is auto-standby mode, which is internally triggered by periodic sensing, and the other is a manual standby mode, which is executed by clamping the secondary output. in general applications, the manual standby mode reduces the input power further compared to auto-standby mode.
str-x6757主要特性和优势:
▪ quasi-resonant topology ic- low emi noise and soft switching
▪ bottom-skip mode- improved system efficiency over the entire output load by avoiding increase of switching frequency
▪ auto-standby mode- lowers input power at very light output load condition
▪ avalanche-guaranteed mosfet- improves system-level reliability and does not require vdss derating
▪ 650 vdss / 0.62 ω rds(on)
▪ various protections - improved system-level reliability
▫ pulse-by-pulse drain overcurrent limiting
▫ overvoltage protection (bias winding voltage sensing),with latch
▫ overload protection with latch
▫ maximum on-time limit
str-x6757应用:
set top box
lcd pc monitor, lcd tv
printer, scanner
smps power supplies
图1.str-x6757方框图
图2.str-x6757典型应用电路
