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UC3843: Asking about components in UC3843 circuit

Tri Dinh
Prodigy 40 points
Part Number: UC3843
Other Parts Discussed in Thread: UC2842, UCC28C42, UC2843

Hi, I am Tri from Vietnam.

I am doing the DC-DC 230VAC to 12VDC application. And UC3843 is used in this case. But I get stuck to some problems. Please help me to solve it!

Question 1: I'd like to ask about two diodes Zener between VCC & OUTPUT and OUTPUT & GND pins, I don't see any recommendations or equations to calculate this one. Could you please tell me how to determine it? ( I chose diode Zener 18V-1W between VCC - OUTPUT, 12V-1W between OUTPUT - GND by myself, is it right?)

Question 2: I chose Css = 10 nF and Rss = 10k ohm in Solf Start function, is it ok?

Question 3: Because I see Design Example Schematic on page 22 use UC2842. So if I use UC3843, do I need to change any components or parameters?

Note: Fsw is selected to be 110KHz same as example schematic.

Sorry if I got any mistakes because my English is limited.