TL431 Voltage-regulator

As mentioned earlier, TL431 contains a 2.5V reference voltage internally, so when output feedback is introduced at the REF end, the device can control the output voltage through a wide range of shunt from the cathode to the anode. As shown in the above figure, when the resistance values of R1 and R2 are determined, they introduce feedback on the partial voltage of Vo. If Vo increases, the feedback amount increases, and the shunt of TL431 also increases, leading to a decrease in Vo. It is evident that this deep negative feedback circuit must stabilize at VI equal to the reference voltage, where Vo=(1+R1/R2) Vref. Choosing different values of R1 and R2 can result in any range of voltage output from 2.5V to 36V, especially when R1=R2, Vo=5V. It should be noted that when selecting a resistor, it is necessary to ensure that the necessary condition for TL431 to operate is that the current passing through the cathode should be greater than 1mA.