need help in smps design

[anzilkhan]

i have made some slight modifications (for 14v, 7amps) to the circuit attached (using top 250). i used tl431 instead for the zener diode . I am not able to obtain 14v output. I am getting a 23 volt output. When i adjust the resistors in its network the voltage increases, but never comes down. Plz help.....

 

[harimelath]

i have made some slight modifications (for 14v, 7amps) to the circuit attached (using top 250). i used tl431 instead for the zener diode . I am not able to obtain 14v output. I am getting a 23 volt output. When i adjust the resistors in its network the voltage increases, but never comes down. Plz help.....

Hi
Probably your RF1 and RF2 values are wrong, you need to get 2,5v at 14v input with the divider at the adjust pin of TL431.
This will help you.
I suggest you can put a pot in RF2 and adjust to correct voltage.
thanks
Hari

 

[anzilkhan]

Hi
Probably your RF1 and RF2 values are wrong, you need to get 2,5v at 14v input with the divider at the adjust pin of TL431.
This will help you.
I suggest you can put a pot in RF2 and adjust to correct voltage.
thanks
Hari

In my design RF2=47k and RF1=12k.I'm getting Vref=4.1 v.Wt does it mean???can u help...