Introduction of TL431

Introduction of TL431

TL431 is a three terminal adjustable shunt reference source with good thermal stability performance. Its output voltage can be arbitrarily set to any value within the range of Vref (2.5V) to 36V using two resistors.

The 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. In the circuit shown in Figure 4, when the resistance values of R1 and R2 are determined, they introduce feedback to the partial voltage of Vo. If V o increases, the feedback amount increases, and the partial voltage 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 plus R1/R2) Vref. Choosing different values of R1 and R2 can result in any voltage output within the range of 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 must be greater than 1 mA