What Is the TL431? Adjustable Voltage Reference: Terminals and Uses
The TL431 is an adjustable precision shunt voltage reference (like a programmable zener). Its internal reference is ~2.495 V and its output is programmable from 2.5–36 V with two resistors (V=Vref×(1+R1/R2)). It is very common in SMPS feedback (usually with an optocoupler). The pin order varies by package — verify it in the datasheet.
The TL431 is an adjustable precision shunt voltage reference (think of it as a programmable zener). With two resistors its output is programmable from 2.5 V to 36 V; its internal reference is ~2.495 V. For the concept, see what is a voltage reference.
What is the TL431 used for?
The feedback reference in switching power supplies (SMPS), precise voltage clamping in place of an adjustable zener, voltage-monitor/threshold circuits and analog designs that need a precise reference. Together with an optocoupler it is very common in isolated SMPS feedback.
TL431 terminals and programming
The TL431 has three terminals: Cathode, Anode and Reference (Ref). The Ref terminal controls the cathode voltage: when Ref reaches the internal reference (2.495 V), the device starts to sink current from cathode to anode. The output voltage is:
VKA = Vref × (1 + R1 / R2) (Vref ≈ 2.5 V)
⚠️ The pin order VARIES by package and manufacturer (TO-92, SOT-23, etc. are laid out differently). Before wiring, always verify the pinout in the datasheet of the exact part you use — see what is an MPN.
Key electrical specifications
| Parameter | Typical value |
|---|---|
| Internal reference | ~2.495 V |
| Programmable output | 2.5 V – 36 V (with two resistors) |
| Cathode current | ~1 mA – 100 mA |
| Packages | TO-92, SOT-23, SOIC, etc. |
Limitations
- It is a reference/shunt, not a power regulator; it does not directly supply load current (it is used in SMPS feedback).
- The cathode capacitor for stability must be chosen per the datasheet (it can oscillate in some regions).
- The pin order is package-dependent — wrong wiring is the most common mistake.
TL431 equivalents and alternatives
- TL432: a sibling with a different pin arrangement.
- LM431 / KA431: close equivalents.
- LM4040 / LM336: fixed precision references.
Find it in our catalog
To compare price and stock for the TL431 and its alternatives, use the TL431 search.