Problem with VIper16 converter

enric · ‎2011-04-19

Posted on April 19, 2011 at 16:21

We made a design with Viper16 to convert from 500V to 12V, non isolated. We followed the guidelines indicated in the document ST_ID15232_rev3 and datasheet. This device has a LIM input, to be used for setting the limit current. We left the LIM pin open, as indicated for the technical papers, to set the limit current as default. The device is not working correctly because the LIM pin is very sensitive. Only touching this pin with the finger, the 12V output goes down, making the output unstable. We would like to know if anyone had the same problem and how did you solved.

mehmetkozig · ‎2011-07-31

Posted on July 31, 2011 at 11:18

Hello

I made a buck converter design with viper16 and i followed AN2872. However my circuit not works properly.

I want to mention about my experience;

When there was any load and no 15V zener diode and no 7805, output voltage increased continuously.

When there is only 10k resistor, output voltage oscilatted between 11V to 13V.

When there is only 1k resistor, output voltage oscilatted between 1V to 4V.

I thought that the problem came from fb pin, so i measured fb pin's voltage which is 0.054V. This must be 3.3 V. Therefore i increased C8 from 100n to 1u. Finally C8 voltage increased but fb pin's voltage didn't change.

(I didnt assemble lim resistor)