TL431A - Adjustable 2.5-36V Precision Shunt Regulator | TI
Référence : TL431A ✓ Actif| Qté | Prix unitaire | Total |
|---|---|---|
| 1 | $0.25 | $0,25 |
| 10 | $0.21 | $2,10 |
| 100 | $0.14 | $14,00 |
| 500 | $0.1 | $50,00 |
| 1 000 | $0.08 | $80,00 |
TL431A Présentation
A shunt regulator or programmable voltage reference is a type of voltage reference IC that maintains a stable voltage across its terminals by sinking excess current, sitting in parallel with the load rather than in series. Within the power management hierarchy, the TL431A belongs to the voltage reference family, alongside series LDO regulators and Zener diode solutions, and it functions effectively as a precision, adjustable replacement for Zener diodes with far tighter tolerance and lower dynamic impedance.
Key features include the 1% initial reference tolerance of the A grade (vs 0.5% for B grade and 2% for standard grade), a wide 2.5V to 36V adjustable output range, low typical output impedance of 0.2 ohm, and sharp turn-on characteristics provided by active output circuitry. The device is specified with thermal stability over automotive, commercial, and military temperature ranges.
Architecturally, the TL431A integrates an internal 2.495V bandgap reference feeding an op-amp comparator that drives an output transistor; when the REF pin voltage exceeds the internal reference, the device begins shunting cathode current, closing the loop in feedback applications. This makes it the de facto industry-standard feedback element in isolated flyback and forward SMPS designs driving optocoupler LEDs.
Typical applications include SMPS feedback error amplification, adjustable Zener replacement in linear supplies, voltage monitors and comparators with built-in reference, and current-source/sink circuits in industrial and consumer power systems.
When setting the output voltage with a resistor divider, use 1% or better resistors and provide at least 1mA continuous cathode current to guarantee regulation accuracy over temperature.
This page synthesizes distributor pricing, verified drop-in alternatives, practical design notes, and parametric comparisons not consolidated in the manufacturer datasheet.
Alternatives de remplacement direct pour TL431A — même boîtier, compatible broche à broche. Les références à boîtier différent nécessitant une retouche du PCB sont exclues.
Variantes de cette série
Modèles de la même série directement compatibles avec TL431A (même facteur de forme et même empreinte) — différant par Minimum Cathode Current for Regulation, Package, Reference Voltage (Vref), Typical Output Impedance.
Outil de comparaison rapide — sélectionnez des références alternatives pour une comparaison côte à côte :
TL431ACDBZR
✅ Remplacement direct✓ En stock
$0.07 / unité
Voir la fiche technique →TL431BCDBZR
✅ Remplacement direct✓ En stock
$0.04 / unité
Voir la fiche technique →TL431AIY
✅ Remplacement direct ⚠️ Spécifications non vérifiées📋 Alternative de référence (hors catalogue)
KA431AZ
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
AZ431AZ-AE1
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
KIA431
✅ Remplacement direct📋 Alternative de référence (hors catalogue)
TL431A Valeurs maximales et caractéristiques électriques
| Topologie | Adjustable shunt regulator / programmable reference |
| Reference Voltage (Vref) | 2.495 V typical |
| Initial Tolerance (25C) | 1% (A grade) |
| Adjustable Output Range | 2.5 V to 36 V |
| Minimum Cathode Current for Regulation | 1 mA |
| Maximum Cathode Current | 100 mA |
| Output Impedance | 0.2 ohm typical |
| Maximum Input Voltage (cathode) | 36 V |
| Turn-on Characteristics | Sharp, active output circuitry |
| Temperature Stability | Specified over automotive, commercial, and military temperature ranges |
| Boîtier | SOT-23 (DBZ), 3-pin |
| Type de montage | Surface Mount |
| Number of Terminals | 3 |
| Replacement For | Zener diodes with improved performance |
| Statut RoHS | Compliant |
| Available Grades | B (0.5%), A (1%), standard (2%) |
| Companion Device | TL432 (same specs, different pinout on DBV/DBZ/PK) |
Configuration des broches de TL431A
| Broche 1 | REF — Reference input - threshold at 2.495V; connect to output divider |
| Broche 2 | ANODE — Anode terminal - connect to lowest potential / ground |
| Broche 3 | CATHODE — Cathode terminal - shunts current when REF exceeds Vref; up to 100mA, 36V max |
Applications typiques
TL431A convient pour 6 applications: SMPS Feedback Error Amplification, Adjustable Zener Diode Replacement, Voltage Monitor and Threshold Comparator, Precision Current Source and Sink, Linear Power Supply Regulation, Automotive and Industrial Voltage Supervision.
SMPS Feedback Error Amplification
The TL431A is the de facto industry-standard error amplifier in isolated flyback and forward converters. Its 2.495V reference with 1% A-grade tolerance directly sets the output regulation point via a resistor divider across the secondary rail, while the cathode drives an optocoupler LED (such as through a PC817 or similar) to close the isolation barrier loop. The sharp turn-on characteristics and 0.2 ohm output impedance give the loop high DC gain, translating directly into tight line and load regulation, often better than 1% over the full operating range. The device operates from 1mA to 100mA cathode current, giving flexibility in biasing the optocoupler for adequate CTR over lifetime. Compared with discrete op-amp plus reference solutions, the TL431A saves board area and cost while providing guaranteed stability behavior extensively documented in power supply design literature.
Recommandé
Adjustable Zener Diode Replacement
Per the Diodes Incorporated and TI datasheets, the 431 family explicitly replaces Zener diodes where improved performance is required. A standard 5.1V Zener carries 5% tolerance and tens of ohms of dynamic impedance; the TL431A set to the same voltage achieves 1% initial accuracy with a programmable value from 2.5V to 36V and only 0.2 ohm typical output impedance, improving clamp accuracy and reducing output ripple fed through the reference. It requires only two resistors plus optional compensation capacitance, occupying less PCB area than many Zener solutions at similar cost. Because the device actively shunts rather than avalanche-breaks, knee sharpness is far superior, benefiting low-current bias tasks such as comparator thresholds and gate references where a soft Zener knee would create threshold drift across load and temperature.
Recommandé
Voltage Monitor and Threshold Comparator
The TL431A functions as a comparator with a built-in precision reference: when the REF pin crosses 2.495V, the cathode pulls low, capable of sinking up to 100mA - enough to drive a relay coil driver, LED indicator, or microcontroller interrupt input directly through a pull-up. Divider resistors set the trip threshold anywhere above 2.5V, and the 1% A-grade tolerance gives a worst-case threshold error of about 25mV at the 2.5V trip point before divider tolerance. Hysteresis is added with a small feedback resistor from cathode to REF, making the circuit a clean under/over-voltage detector for battery monitors, supply sequencing supervisors, and fault latch circuits in industrial equipment, all in a 3-pin SOT-23 footprint costing cents.
Recommandé
Precision Current Source and Sink
By placing a sense resistor between the anode/ground node and forcing the REF pin to sense across it, the TL431A forms a two-terminal precision current source or sink: I = 2.495V / Rsense. The 1% reference tolerance limits current accuracy error to roughly 1% before resistor tolerance, dramatically better than transistor Vbe-based current sources that drift several percent per 25C. Applications include LED bias strings, sensor excitation currents, and pull-up currents for 4-20mA transmitter front ends. Designers should verify the compliance voltage stays within the 36V maximum and maintain at least 1mA shunt current for regulation. The 0.2 ohm output impedance and sharp turn-on ensure stable current behavior across load swings documented in the TI datasheet application circuits.
Recommandé
Linear Power Supply Regulation
In series linear regulators, the TL431A serves as the error amplifier comparing an output divider against its 2.495V reference and driving the base of an NPN pass transistor, yielding a low-cost adjustable regulator for outputs from 2.5V up to tens of volts. The high open-loop gain of the TL431 delivers output ripple rejection and load regulation that a plain Zener-pass circuit cannot achieve, while the A-grade 1% reference removes the need for output trim in most consumer and industrial supplies. A compensation network at the cathode stabilizes the loop with the pass transistor gain. This topology remains popular in auxiliary bias supplies, white-goods controllers, and battery chargers where an integrated regulator IC is unnecessary and the 100mA shunt capability comfortably drives the pass element.
Recommandé
Automotive and Industrial Voltage Supervision
The TI TL431 family is specified with thermal stability over automotive, commercial, and military temperature ranges per the datasheet, making the TL431A suitable for automotive battery-rail monitoring, 24V industrial bus supervision, and under-voltage lockout functions. Divider ratios map 12V or 24V rails onto the 2.495V REF threshold, and the cathode output drives status LEDs, MCU inputs, or reset-generation circuits. The wide 2.5V to 36V operating range tolerates automotive load-dump-protected rails when combined with upstream transient suppression, and the 1% reference accuracy keeps fault thresholds within specification across the full temperature envelope. Its three-pin SOT-23 footprint and commodity pricing enable per-channel supervision at negligible BOM cost in multi-rail industrial controllers.
Recommandé
Récapitulatif des produits recommandés
Données de référence d'ingénierie pour TL431A — comparaison, recommandations de conception et informations de conformité.
Guide de sélection
Comparaison avec les alternatives
| Paramètre | Ce produit | TL431ACDBZR | TL431B | KA431AZ | AZ431AZ-AE1 | KIA431 |
|---|---|---|---|---|---|---|
| Package | SOT-23 (DBZ) | SOT-23 (DBZ) - same | SOT-23 (DBZ) - same | SOT-23 (DBZ) - same | SOT-23 (DBZ) - same | SOT-23 (DBZ) - same |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | onsemi | Diodes Incorporated | KEC |
| Initial Reference Tolerance (25C) | 1% (A grade) | 1% (A grade) | 0.5% (B grade) | 2% (AZ grade) | 2% (AZ grade); AB suffix = 0.5% | grade-dependent (1-2%) |
| Adjustable Output Range | 2.5 V to 36 V | 2.5 V to 36 V | 2.5 V to 36 V | 2.5 V to 36 V | 2.5 V to 36 V | 2.5 V to 36 V |
| Maximum Cathode Current | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA |
| Reference Voltage | 2.495 V typical | 2.495 V typical | 2.495 V typical | 2.495 V typical | 2.5 V nominal | 2.495 V typical |
| Output Impedance | 0.2 ohm typical | 0.2 ohm typical | 0.2 ohm typical | 0.2 ohm typical | 0.2 ohm typical | 0.2 ohm typical |
| Minimum Cathode Current | 1 mA | 1 mA | 1 mA | 1 mA | 1 mA | 1 mA |
Principaux différenciateurs
- 1% A-grade reference tolerance (vs KA431AZ)
- Optional 0.5% accuracy upgrade on identical footprint (vs TL431B)
- True industry-standard second sourcing (vs AZ431AZ-AE1)
Notes de conception
Guarantee at least 1mA of continuous cathode current under all operating conditions. If the load the TL431A shunts can drop (for example, when the optocoupler LED current is at its minimum during light load), the device may fall out of regulation and output voltage will drift high. Size the pull-up resistor from the supply to the cathode so that even at maximum output voltage, (Vsupply - VOUT)/Rpullup - Idiv - Iopto >= 1mA. The maximum is 100mA; also check power dissipation P = (VKA - VANODE) x IK against SOT-23 thermal limits.
The TL431 is internally a high-gain op-amp plus reference, and it is conditionally stable: not every cathode capacitance is safe. In isolated SMPS feedback loops, add a compensation network (typically an RC from cathode to REF for integrator behavior) and verify the loop crossover with a bode plot. Datasheet application sections document stable capacitance ranges at the cathode; a small capacitor directly on REF can also slow the response for comparator-style use to reject noise. Ignoring stability compensation is the most common cause of TL431 oscillation in production SMPS designs.
Use 1% or better, low-TC resistors for the REF divider since output accuracy is Vref x (1 + R1/R2); divider error multiplies directly into output error. Keep the divider physically close to the REF pin and route it away from switching nodes to prevent ripple injection into the reference. Provide a solid low-impedance connection from the anode pin to the local ground reference, because milliohms of shared ground impedance with high pulsed loads appears as reference error in shunt and feedback configurations.
Informations de conformité
The TL431 family is specified over automotive temperature ranges per TI datasheet; specific AEC-Q100 qualification must be confirmed on the exact orderable suffix. REACH/halogen status not stated in provided data.
