Thanks Dave much appreciated. Unfortunately I don't have a TL431 on-hand but i did later find two M5236L linear regulator IC's . I haven't much looked at any circuits for it other than the example circuits that were included in the data sheets, hoping i can use that instead. We were hit with another snowstorm recently so digging out yet again and don't have much time for anything else, will get back to this in better times. thanks again.

 

Finally getting back to this project after nearly a year, how time flies.

As mentioned in my other SMPS thread, ive decided not to use the board for a battery charger and instead will be using it to build a bench DC power supply. Plan is to have four outputs ; +3.3 volts , +5 volts , +12 volts and a variable 0 to +30 volts DC. The fixed volts are a given but the 0 to 30 volts im not quite sure of yet. I'd like to modify the existing shunt regulator circuit to make it variable or atleast as close to 0 to 30 volts as possible. The idea i had was to replace the fixed resistors in the voltage divider section of the TL431 with a potentiometer (50K ?) so as to sweep the entire voltage range from 0 to +30 volts if possible.

Ive attached a schematic and pictorial of that section of the board for clarity.