Electronic – Difference between TL431 and TL432

It will work, but it will not be very stiff.

(3.135V - 3V) / 560R gives 241 microamps. If the load is higher than that, the voltage drop across the 560 ohm resistor will lower the input voltage to below the setpoint you want.

Typically you should allow the 431 to eat 1 mA to keep all of the datasheet assumptions in check. You should go with a lower series resistor - 51R allows 2.65mA at minimum input. The 431 can safely eat a few milliamps so don't worry about power.

A quick analysis shows the lowest voltage = 2.980V, the highest 3.012V (nominal 2.996V) so we're looking at +/- 0.53%. Worst-case setpoints are when the two resistors are at opposite ends of the tolerance spectrum (one large, one small).

Note that TL431 have three pins. U1 "measures" the voltage across R7 which is proportional to the output voltage because R6 & R7 is configured as a voltage divider. If the voltage across R7 is above 2.495V (see TL431 datasheet) it will "open" and current will flow trough R4, the opto coupler and U1 to ground. The voltage drop over the opto coupler doesn't matter because unlike a zener diode, U1 have a separate voltage sense pin.