Adjustable shunt reference — the classic TL431 in a TO-92-3
The Texas Instruments TL431CLPRE3 is the through-hole version of the industry-standard TL431 adjustable shunt voltage reference. It provides a 2.495 V nominal reference that can be programmed up to 36 V with two external resistors, making it a staple for power-supply feedback loops, precision current limiting, and voltage monitoring in commercial-temperature equipment.
±2.2% tolerance — where it lands in the accuracy stack
The ±2.2% initial tolerance places this TL431CLPRE3 in the standard-grade bin of the TL431 family. For a 5 V output rail, that's roughly ±110 mV of reference error before resistor divider tolerances. If your design needs tighter regulation — say for an ADC reference or a precision current source — you'd step up to a 0.5% or 0.1% TL431 variant, or to a series reference like the LM4132AMF-4.1/NOPB which offers ±0.05% tolerance. For general-purpose feedback in an off-line flyback or a linear regulator, the 2.2% grade is adequate and cost-effective.
100 mA cathode current — sizing the bias resistor
The TL431CLPRE3 can sink up to 100 mA at the cathode, with a minimum operating current of 1 mA. That 100 mA ceiling sets the maximum load the shunt can regulate — for a typical feedback application drawing a few milliamps, there's ample headroom. The bias resistor from the supply to the cathode must be sized so the current through the TL431 stays between 1 mA and 100 mA over all line and load conditions.