I want to solve the problem for the LNK3209 buck converter.

Hello Everybody!



I'm going to make a buck converter using LNK3209. I have referred to the example circuit in the LNK320X datasheet.

My goal is to make 20V/500mA output power for AC220V /60HZ input.

 

To test the LKN3209 basic operation, I tested Fig.1 circuit(12V output circuit), but it did not operate.

It operated under DC 60V input condition, but the output was unstabled and fluctuated when over 60V input.

The output variation was from 3Vp to 15Vp. I don't know why?



Q1: It does not operate in the case of stabled DC power input.?

Do I have to use the bridge circuit with a capacitor for AC220 input.? The ripple signal is be related?



Q2: I have modified the 12V circuit for the 20V output circuit (Fig.2).

Same as Fig1, DC20V (0.5A) output was OK when 60V input, but over 60V (for example DC100V input condition), the output was not normal operation. The output variates from 3Vp ~ 25Vp.



I don't know why? Let me know the reason why and my mistakes.



Thanks