The TL431’s operation is actually pretty simple. When the voltage at the reference pin is above 2.5V, the output transistor conducts. When the reference voltage falls below 2.5V, the device ...

We had to look at the TL431 data sheet for this one and shamefacedly admit that since we’d only ever used the chip as a voltage reference, we hadn’t appreciated this capability.

Voltage Reference . The Texas Instrument TL431 is an inexpensive programmable shunt regulator. In this circuit, it is applied at the minimum voltage (2.5V) and does not require the usual voltage ...

Internally, the TL431 comprises a precision voltage reference, an operational amplifier, and a shunt transistor (Figure 1a). In a typical voltage-regulator application, adding two external resistors, ...

The TL431's internal functional blocks consist of a 2.5V reference connected to an op-amp's negative input, with the op-amp output used to drive an open collector transistor's base.

When the potential at the reference junction of D3 reaches the reference, about 2.495 V, D3 begins to function as a shunt regulator sinking current at its cathode and turning on the LED through D2.