negative tl431
Try to check the pin reversals. As you put the chip facing you and pins downwards, pins counted left to right in the order
1. Reference
2. Anode
3. Cathode.
The anode will face 220Ω resistor and it is also output and one side of R1. cathode (pin3) will be common negative and also R2 other lead. R1,R2 junction to got to pin1. R2.
one side of 220Ω will be +ve input.
Mostly I suspect pin reversals of the IC.
Check up and it should work and withe set up you get 5V output if you provide atleast 8V as input.
Sarma