About UC3843 & UCC3803

The project used UC3843 with 12V power supply. Now  the  power  supply  is  changed to  5V, So IC changed to  UCC 3803.Only the IC is changed, and the peripheral circuit is not changed, The  Circuit  as  follows:

1>When  used   5V   power supply,  The output of the sixth pin is abnormal, and the third pin is the waveform above， the waveform as  follows：

2>When  used   5.5V   power supply,  The output of the sixth pin is normal，the waveform as  follows：

3>There is a board, the input voltage must reach 8.5V, and the sixth pin can be switched normally，the  waveform as  follows：

4>modify the working frequency from 100K to more than 900 K，the output of the sixth pin is   abnormal，the waveform as  follows：

Johnsin Tao：

HI

   两个芯片是由差别的，不能直接取代，不仅仅是供电的问题，你可以再UC3843电路的基础上改，结合如下文档：

   DN-42A Design Considerations for Transitioning from UC3842 to the New UCC3802