TL431 - Adjustable 2.5-36V Shunt Regulator | Texas Instruments
MPN: TL431 β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.18 | $0.18 |
| 10 | $0.15 | $1.50 |
| 100 | $0.11 | $11.00 |
| 500 | $0.08 | $40.00 |
| 1,000 | $0.06 | $60.00 |
Drop-in alternatives for TL431 β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
TL431LI
β Drop-Inπ Reference alternative (not in catalog)
TL431AID
β Drop-Inπ Reference alternative (not in catalog)
TL432
β‘ Same Packageπ Reference alternative (not in catalog)
TL431A
β Drop-Inπ Reference alternative (not in catalog)
TL431A
β Drop-Inπ Reference alternative (not in catalog)
AZ431
β Drop-Inπ Reference alternative (not in catalog)
KA431
β Drop-Inπ Reference alternative (not in catalog)
TL431 Maximum Ratings & Electrical Characteristics
| Output Type | Adjustable shunt |
| Reference Voltage (Vref) | 2.495 V typical |
| Reference Tolerance (B grade) | 0.5% at 25C |
| Reference Tolerance (A grade) | 1% at 25C |
| Reference Tolerance (standard grade) | 2% at 25C |
| Adjustable Output Range | 2.495 V to 36 V |
| Maximum Cathode Voltage | 36 V |
| Cathode Current Range | 1 mA to 100 mA |
| Output Impedance | 0.2 ohm typical |
| Reference Input Current | 4 uA typical |
| Temperature Range (commercial) | 0C to +70C |
| Temperature Range (automotive) | -40C to +125C |
| Packages | TO-92, SOIC-8, SOT-23 (DBV), SOT-23-3 (DBZ) |
| Mounting Type | Through Hole (TO-92) / Surface Mount |
| RoHS Status | Compliant |
| Pinout Family | TL431 standard; TL432 variant has different pinout for DBV/DBZ/PK |
TL431 Pin Configuration
| Pin 1 | REF β Reference input (2.495V threshold), TO-92 (LP) package |
| Pin 2 | ANODE β Anode, connected to circuit ground return, TO-92 (LP) package |
| Pin 3 | CATHODE β Cathode, shunt current terminal, up to 36V, TO-92 (LP) package |
Safe Operating Area (SOA) & Thermal Characteristics
No official SOA curve available for this component. Always operate within absolute maximum ratings specified in the datasheet. Ensure adequate cooling and derate as needed.
Typical Applications
TL431 is suitable for 6 applications: SMPS Optocoupler Feedback, Adjustable Zener Replacement, Constant Current Source and Sink, Voltage Monitor and Comparator, Precision Series Regulator Error Amp, Automotive Power Systems.
SMPS Optocoupler Feedback
The dominant TL431 use case: it acts as the error amplifier in the secondary-side feedback loop of flyback and forward converters. The output voltage divider drives the REF pin; when Vout divided exceeds 2.495V, the TL431 sinks current through the optocoupler LED, modulating the primary-side PWM duty cycle. Its 0.2 ohm dynamic impedance and 36V cathode rating suit 5V/12V/24V outputs, while a compensation network (typically a capacitor plus RC from cathode to REF) stabilizes the loop. TI application circuits in the TL431 datasheet show the standard bias-resistor values.
Recommended
Adjustable Zener Replacement
The TL431 replaces Zener diodes wherever a precise, programmable clamping voltage is needed. Unlike a Zener, its 2.495V reference has low temperature drift and a sharp knee: the output impedance is 0.2 ohm typical versus tens of ohms for Zeners, giving far better regulation. Two resistors program any clamp from 2.495V to 36V, and the 1mA to 100mA cathode range covers most clamp currents. This eliminates Zener grading and improves accuracy from the typical 5% Zener tolerance down to 0.5% with B-grade TL431 devices.
Recommended
Constant Current Source and Sink
With a sense resistor between anode and REF, the TL431 forms a precise two-terminal current source or sink: I = 2.495V / Rsense. Because the reference accuracy reaches 0.5% (B grade), current accuracy is limited mainly by resistor tolerance, and the 36V cathode rating allows high-compliance operation. Typical uses include LED bias, base drive biasing, and pull-up current sources in analog front ends. The 1mA minimum cathode current defines the floor of usable current regulation per TI datasheet application circuits.
Recommended
Voltage Monitor and Comparator
Because the TL431 behaves like a transistor with a sharp 2.495V threshold, it functions as a low-cost voltage comparator with a built-in reference. A divider scales the monitored rail to the REF pin; crossing the threshold snaps the cathode low, sinking up to 100mA enough to drive an LED, relay, or optocoupler directly. Add slight positive feedback (hysteresis) via a resistor from cathode to REF for clean switching in undervoltage/overvoltage detection, battery monitoring, and power-good indication circuits.
Recommended
Precision Series Regulator Error Amp
Pairing the TL431 with a pass transistor (BJT or MOSFET) creates a discrete adjustable series regulator with accuracy set by the 0.5% B-grade reference. The TL431 compares the divided output against 2.495V and drives the pass element base or gate. This architecture achieves performance near monolithic LDOs at very low cost, with the output settable from 2.495V to 36V. Typical companion choices include small-signal BJTs for loads under 1A, and it complements TI linear regulator families where adjustable reference accuracy matters.
Recommended
Automotive Power Systems
Automotive-grade TL431 versions operate from -40C to +125C, per the TI and ST datasheets, making them suitable for feedback regulation, lamp-drive regulation, and monitoring rails in 12V automotive electrical systems where the 36V cathode rating covers load-dump-adjacent conditions when combined with proper protection. Accuracy grades up to 0.5% support sensor-rail monitoring. For functional-safety designs, verify the specific orderable suffix qualification on the TI product page before final selection.
Recommended
Recommended Products Summary
Engineering reference data for TL431 β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | TL431LI | TL431A (onsemi) | AZ431 |
|---|---|---|---|---|
| Package | TO-92 / SOIC-8 / SOT-23 | TO-92 / SOIC-8 / SOT-23 - same | TO-92 / SOT-23 - same | TO-92 / SOT-23 - same |
| Brand | Texas Instruments | Texas Instruments | onsemi | STMicroelectronics |
| Reference Voltage | 2.495 V | 2.495 V | 2.495 V | 2.495 V |
| Reference Accuracy (best grade) | 0.5% (B grade) | 0.5% (B grade) with lower Iref | 1% (A grade) | 1% (A grade) |
| Max Output (Cathode) Voltage | 36 V | 36 V | 36 V | 36 V |
| Max Cathode Current | 100 mA | 100 mA | 100 mA | 100 mA |
| Reference Input Current | 4 uA typical | Lower, optimized Iref/Idev | [DATA_NEEDED] | [DATA_NEEDED] |
| Pin Compatibility | Industry-standard REF/A/K | Pin-to-pin compatible | Different pinout in DBV/DBZ/PK | Pin-to-pin compatible (TO-92) |
Key Differentiators
- Industry-standard de facto pinout with massive second-source ecosystem (vs TLV431)
- Best-in-class 0.5% accuracy option (B grade) (vs KA431)
- Higher accuracy successor available pin-to-pin (vs TL431LI)
Design Notes
The TL431 is a high-gain feedback device: in SMPS feedback loops, parasitic capacitance from cathode to REF can cause instability. Place a compensation network (typ. 100nF in series with a small resistor) from cathode to REF, sized per TI application guidance for your optocoupler CTR and loop bandwidth. Also never let cathode current fall below 1mA - regulation is not guaranteed below this and output voltage drifts high.
In shunt operation the bias resistor must both supply the minimum 1mA cathode current plus load current at minimum input voltage, and keep cathode current under 100mA and power under the package limit at maximum input. For a 5V output monitor from a 12V rail, a ~5.6k bias resistor typically satisfies both bounds. Verify worst-case power dissipation in the TO-92 package, which has the poorest thermal performance.
Use 1% or better divider resistors to preserve the 0.5% (B-grade) reference accuracy; divider error often exceeds reference error. For low-power monitoring, remember the 4uA typical REF input current creates divider error - choose divider current at least 100x larger, or switch to the TL431LI whose optimized Iref reduces this error source.
Compliance Information
RoHS compliance per TI product page for current production suffixes; verify exact orderable suffix compliance on ti.com. Automotive temperature grades exist but AEC-Q100 qualification must be confirmed per specific suffix.
