Shunt reference for feedback and biasing
The Texas Instruments LMV431CZ/NOPB is a low-voltage adjustable shunt reference in a TO-92-3 through-hole package. It operates as a three-terminal programmable Zener diode: two external resistors set the output voltage anywhere from the 1.24 V internal bandgap up to 30 V. The 1.5% tolerance is tighter than the classic TL431's 2.2% grade — useful when the feedback divider resistors already contribute their own 1% drift and the output regulation budget is tight. With a 15 mA output current capability, it comfortably drives the optocoupler LED in an isolated flyback or forward-converter feedback loop. The minimum cathode current is 80 µA — keep the bias resistor sized so the device sees at least this much current at the lowest input voltage, or regulation drops out.
Package and temperature grade
The TO-92-3 package is the same three-lead footprint used by the TL431 and many linear regulators. It is through-hole, hand-solderable, and fits standard 0.1-inch pitch prototyping boards. The bulk packaging means it ships in tubes or bags — no reel for pick-and-place, so factor in manual insertion or a tube feeder for volume assembly. This covers benchtop power supplies, telecom indoor equipment, and consumer electronics. For an engine-bay or outdoor enclosure that sees -20°C, look at the industrial-grade LMV431AIM5 or similar.
It is ROHS3 compliant, so no RoHS exemption expiry to track for EU or California market shipments.