η -BalanceTM  PWM Power Switch  Fixed 50KHz Fsw

Product：SF1539

一、General Description 

SF1539 is a high performance, high efficiency, highly integrated current  mode  PWM   power   switch   for offline flyback converter applications. 

In SF1539, PWM switching frequency with shuffling is fixed to 50KHz and is trimmed to tight range. When the  output power demands  decrease,   the  IC decreases  switching    frequency  based  on  the proprietaryη  -BalanceTM  control  to   boost  power conversion  efficiency  at  the light load.  When  output power  falls  below  a  given  value,  the  IC  enters  into burst mode and provides excellent efficiency without audio noise.

The IC can achieve “Zero OCP/OPP Recovery Gap” using SiFirst’s proprietary control algorithm. Meanwhile, the OCP/OPP variation versus universal line input is compensated

The IC has built-in synchronized slope compensation to prevent sub-harmonic oscillation at high PWM duty output. The IC also has built-in soft start function to soften  the  stress  on  the  MOSFET  during  power  on period.

SF1539 integrates functions and protections of Under Voltage  Lockout  (UVLO), VCC Over Voltage Protection  (OVP), Cycle-by-cycle Current Limiting(OCP), Pins  Floating   Protection, Over  Load Protection  (OLP), VCC Clamping,  Leading Edge Blanking (LEB), etc.

SF1539 is available in DIP8 packages.

二、 Features 

   Built-in 600V Power MOSFET 
   Proprietary η  -BalanceTM  Control  to Boost Light Load Efficiency
   Proprietary  “Zero  OCP/OPP  Recovery Gap Contro
   Fixed 50KHz Switching Frequency
   Built-in Soft Start Function
   Very Low Startup Current
   Frequency Reduction and Burst Mode Control for Energy Saving
   Current  Mode Control
   Built-in Frequency Shuffling 
   Built-in Synchronous Slope Compensation
   Cycle-by-Cycle Current Limiting
   Built-in Leading Edge Blanking (LEB)
   Constant Power Limiting
   Pins Floating Protection
  Audio Noise Free Operation
  VDD OVP & Clamp
  VDD Under Voltage Lockout (UVLO)

三、Applications

Offline AC/DC Flyback Converter for

   AC/DC Adaptors 
  Open-frame SMPS
  Set-Top Box Power Supplies
  ATX Standby Power

四、Package/Order Information 

五、Typical Application

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