The TL431-ACP is three-terminal adjustable shunt regulators packaged in 8-pins PDIP, with specified thermal stability over 0° ~ 70°C (commercial grade). The output voltage can be set to any value between Vref (approximately 2.5 V) and 36 V, with two external resistors. This device have a typical output impedance of 0.2 Ω. Active output circuitry provides a very sharp turn-on characteristic, making these devices excellent replacements for Zener diodes in many applications, such as onboard regulation, adjustable power supplies, and switching power supplies. Initial tolerance for class A (at 25°C) is 1%. In addition, low output drift versus temperature ensures good stability over the entire temperature range.

This standard device has proven ubiquity and versatility across a wide range of applications, ranging from power to signal path. This is due to it's key components containing an accurate voltage reference & opamp, which are very fundamental analog building blocks. TL431 is used in conjunction with it's key components to behave as a single voltage reference, error amplifier, voltage clamp or comparator with integrated reference.

TL431 can be operated and adjusted to cathode voltages from 2.5V to 36V, making this part optimum for a wide range of end equipments in industrial, auto, telecom & computing. In order for this device to behave as a shunt regulator or error amplifier, > 1mA (Imin(max)) must be supplied in to the cathode pin. Under this condition, feedback can be applied from the cathode and reference pins to create a replica of the internal reference voltage.

Following is functional block diagram of this integrated circuit (taken from datasheet, p19):