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UCC3858J PDF预览

UCC3858J

更新时间: 2024-11-22 23:39:03
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其他 - ETC 模拟IC
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12页 381K
描述
Analog IC

UCC3858J 数据手册

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UCC1858  
UCC2858  
UCC3858  
PRELIMINARY  
High Efficiency, High Power Factor Preregulator  
FEATURES  
DESCRIPTION  
Programmable PWM Frequency  
Foldback for Higher Efficiency at Light  
Loads  
The UCC3858 provides all of the control functions necessary for active  
power factor corrected preregulators which require high efficiency at low  
power operation. The controller achieves near unity power factor by  
shaping the AC input line current waveform to correspond to the AC input  
line voltage using average current mode control.  
Leading Edge PWM for Reduced  
Output Capacitor Ripple Current  
The operation of the UCC3858 closely resembles that of previously de-  
signed Unitrode PFC parts with additional features to allow higher effi-  
ciency boost converter operation at light loads. This is accomplished by  
linearly scaling back the PWM frequency when the output of the voltage  
error amplifier drops below a predetermined user programmable level in-  
dicating a light load condition. The frequency is scaled back by reducing  
the charging current for the CT ramp (in proportion to the output power),  
and increasing the dead time. There is also an instantaneous reset input  
to pull the IC out of foldback mode quickly when the load comes back up.  
Controls Boost PWM to Near Unity  
Power Factor  
World Wide Operation without  
Switches  
Accurate Power Limiting  
Synchronizable Oscillator  
100µA Startup Supply Current  
Low Power BCDMOS  
The PWM technique used in the UCC3858 is leading edge modulation.  
When combined with the more conventional trailing edge modulation on  
the downstream converter, this scheme offers the benefit of reduced rip-  
ple current on the bulk storage capacitor. The oscillator is designed for  
easy synchronization to the downstream converter. A simple synchroni-  
zation scheme can be implemented by connecting the PWM output of  
the downstream converter to the SYNC pin.  
12V to 18V Operation  
(continued)  
BLOCK DIAGRAM  
UDG-96191-1  
03/99  
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