TL431BQDBZR - 0.5% Adjustable Shunt Reference SOT-23-3 | TI
MPN: TL431BQDBZR ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.28 | $0.28 |
| 10 | $0.22 | $2.20 |
| 100 | $0.13 | $13.00 |
| 500 | $0.09 | $45.00 |
| 1,000 | $0.07 | $70.00 |
TL431BQDBZR Overview
A shunt regulator or shunt voltage reference is a three-terminal device that maintains a precise voltage across its cathode and anode terminals by sinking excess current through itself. In the power-management hierarchy it sits alongside series voltage references and LDO regulators as a fundamental building block: it can act as a standalone voltage reference, as an error amplifier in feedback loops, or as a low-current voltage regulator for auxiliary rails.
Key features include the B-grade ±0.5% reference tolerance at 25 C, Q-grade qualification for the -40 C to +125 C automotive temperature range, low typical output noise of 0.2 uVrms (10 Hz to 10 kHz band cited as 0.2 uV typical in TI legacy datasheets), and low output impedance. The output voltage is programmed with two external resistors, and the device regulates when the reference pin exceeds 2.495 V.
Architecturally, the TL431 combines an internal 2.495 V bandgap reference with an op-amp and output transistor, effectively functioning as an error amplifier whose open-loop gain drives the cathode follower stage. This makes it the de facto standard feedback element in opto-coupled isolated flyback supplies.
Typical applications include secondary-side feedback in isolated SMPS (driving an optocoupler such as the PC817), adjustable shunt regulation for auxiliary 5 V or 12 V rails, comparator and threshold detection circuits, and voltage monitoring in automotive modules.
Design consideration: always bias the device with at least 1 mA of cathode current for regulation and add a small compensation capacitor and resistor from cathode to reference pin to stabilize the feedback loop.
This page synthesizes distributor pricing, drop-in alternatives across TI and Nexperia/onsemi/Diodes, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for TL431BQDBZR — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with TL431BQDBZR (same form factor and footprint) — differing in Package, Operating Temperature Range, Minimum Cathode Current for Regulation, Automotive Qualification, Reference Type.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
TL431BQDBZRQ1
✅ Drop-In📋 Reference alternative (not in catalog)
TL431AQDBZR
✅ Drop-In✓ In Stock
$0.09 / Unit
View Datasheet →TL431BIDBZR
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
TL431BQDBZR-QR
✅ Drop-In📋 Reference alternative (not in catalog)
KA431AZTA
✅ Drop-In📋 Reference alternative (not in catalog)
AZ431AZ-ATRE1
✅ Drop-In📋 Reference alternative (not in catalog)
TL431BQDBZR Maximum Ratings & Electrical Characteristics
| Reference Voltage (Vref) | 2.495 V |
| Reference Voltage Tolerance | ±0.5% (B grade, at 25 C) |
| Adjustable Output Voltage Range | 2.495 V to 36 V |
| Maximum Cathode Current | 100 mA |
| Minimum Cathode Current for Regulation | 1 mA (typical) |
| Device Type | Adjustable Precision Shunt Regulator / Shunt Voltage Reference |
| Temperature Grade | Q grade, -40 C to +125 C |
| Package | SOT-23 (DBZ), 3-pin |
| Mounting Type | Surface Mount |
| Typical Output Noise | 0.2 uVrms (per TI adjustable precision shunt regulator datasheet) |
| Automotive Qualification | Yes (Q grade; TL431BQDBZRQ1 variant available) |
| Number of Pins | 3 |
| RoHS Status | Compliant |
| Packaging | Tape & Reel (T/R) |
| Family Alternatives (grades) | B = 0.5%, A = 1%, standard = 2% initial tolerance |
TL431BQDBZR Pin Configuration
| Pin 1 | REF — Reference input - sense point for output divider; regulates at 2.495 V |
| Pin 2 | ANODE — Anode - lowest potential / ground return terminal |
| Pin 3 | CATHODE — Cathode - output terminal; sinks up to 100 mA to regulate voltage |
Typical Applications
TL431BQDBZR is suitable for 6 applications: Opto-Isolated SMPS Feedback, Adjustable Shunt Voltage Regulation for Auxiliary Rails, Automotive Voltage Monitoring and Threshold Detection, Precision Voltage Reference for ADCs and Comparators, Battery Charger Voltage Regulation, Solar and LED Driver Open-Loop Voltage Clamp.
Opto-Isolated SMPS Feedback
The TL431BQDBZR is the de facto standard secondary-side error amplifier in isolated flyback, forward, and LLC power supplies. Its 2.495 V internal reference senses the output via a precision resistor divider; when the divider exceeds 2.495 V, the device sinks cathode current through the LED of an optocoupler such as the PC817, closing the isolation barrier feedback loop to the primary-side PWM controller. The B-grade ±0.5% reference tolerance directly translates to output-voltage accuracy, enabling ±1% regulation targets without trimming. The 36 V cathode rating covers 5 V, 12 V, and 24 V output rails. Designers must include a compensation network (typically a resistor plus 0.1-1 uF capacitor from cathode to REF) to stabilize the loop bandwidth and avoid oscillation with optocoupler pole.
Recommended
Adjustable Shunt Voltage Regulation for Auxiliary Rails
Used as a standalone shunt regulator, the TL431BQDBZR maintains an adjustable rail from 2.495 V up to 36 V set by two external resistors, sinking up to 100 mA of excess current. This is ideal for low-power auxiliary supplies in industrial meters, home appliances, and white-goods control boards where a precision local rail is needed at minimal BOM cost. Because the device only conducts the current required to hold the voltage, no series regulation transistor is needed for loads under tens of milliamps; a single series resistor from a higher-voltage supply completes the circuit. The Q-grade -40 C to +125 C range permits placement near heat-generating components. Always provide at least 1 mA of bias current so the device stays in regulation at minimum load.
Recommended
Automotive Voltage Monitoring and Threshold Detection
In automotive modules such as body controllers, sensors, and USB charging ports, the TL431BQDBZR works as a precise comparator: the REF pin samples a divided version of the monitored rail, and the cathode pulls low when the threshold is crossed. The B-grade ±0.5% tolerance over the Q-grade -40 C to +125 C range yields a well-defined fault threshold without factory calibration, essential for over-voltage lockout, low-battery detection, and load-dump monitoring. Hysteresis can be added with a resistor from cathode to REF. For formal automotive production programs, the TL431BQDBZRQ1 variant with AEC-Q100 qualification is recommended, drop-in on the same footprint. The 36 V maximum input directly accommodates monitored 12 V automotive buses including transient headroom.
Recommended
Precision Voltage Reference for ADCs and Comparators
The TL431BQDBZR provides a low-cost precision reference for ratiometric ADC measurements, window comparators, and DAC full-scale setting in consumer and industrial designs. The ±0.5% B-grade accuracy, low 0.2 uVrms typical output noise, and low output impedance provide a stable conversion scale for 10-12 bit converters where approximately 1 LSB accuracy targets are acceptable. Buffering the cathode with an op-amp is recommended when driving dynamic ADC reference inputs, because the TL431's output impedance rises at low cathode currents. Operating the device at 5-10 mA cathode current minimizes impedance and noise. The SOT-23 footprint fits dense mixed-signal boards, and the 36 V maximum allows reference generation from 24 V industrial supplies via a single series resistor.
Recommended
Battery Charger Voltage Regulation
In constant-voltage battery chargers for lead-acid and Li-ion packs, the TL431BQDBZR senses the pack voltage through a precision divider and modulates the pass-element drive (or optocoupler in isolated chargers) to hold the termination voltage accurately. The ±0.5% reference accuracy matters directly: for a 4.2 V Li-ion cell, a 0.5% reference error is about 21 mV, well within safe charge tolerance, whereas a 2% standard-grade part could approach overcharge limits. The 36 V rating supports 12 V lead-acid charger outputs. Adding hysteresis or pairing with the charger IC's termination logic gives a complete, low-cost constant-voltage loop. Q-grade temperature range ensures termination accuracy across garage-to-outdoor environments.
Recommended
Solar and LED Driver Open-Loop Voltage Clamp
In solar charge controllers, LED string drivers, and panel-mounted instrumentation, the TL431BQDBZR acts as an open-loop voltage clamp that diverts excess energy when the sensed bus exceeds the programmed threshold. Sinking up to 100 mA, it can directly shunt modest excess current or gate a larger MOSFET for higher-power diversion. The 36 V ceiling suits 12 V/24 V solar buses, and the SOT-23 package dissipates small clamps efficiently when cathode current is limited by a series resistor. Because the device regulates the REF pin to 2.495 V with ±0.5% accuracy, the clamp threshold stays tight over temperature, protecting battery life and LED lumen maintenance. A small RC from cathode to REF filters transients and prevents chatter near the threshold.
Recommended
Recommended Products Summary
Engineering reference data for TL431BQDBZR — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | TL431BQDBZRQ1 | TL431AQDBZR | TL431BQDBZR-QR | KA431AZTA | AZ431AZ-ATRE1 |
|---|---|---|---|---|---|---|
| Package | SOT-23 (DBZ) | SOT-23 (DBZ) - same | SOT-23 (DBZ) - same | TO-236AB (SOT-23 compatible) - same | TO-236AB (SOT-23 compatible) - same | SOT-23 - same |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Nexperia | onsemi | Diodes Incorporated |
| Reference Tolerance | ±0.5% (B grade) | ±0.5% (B grade) | ±1% (A grade) | ±0.5% (B grade) | ±1% (AZ grade) | ±1% (AZ grade) |
| Reference Voltage | 2.495 V | 2.495 V | 2.495 V | 2.495 V | 2.495 V | 2.5 V nominal |
| Adjustable Output Range | 2.495 V to 36 V | 2.495 V to 36 V | 2.495 V to 36 V | 2.495 V to 36 V | 2.495 V to 36 V | Vref to 36 V |
| Max Cathode Current | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA |
Key Differentiators
- Tightest grade in the TL431 family (vs TL431AQDBZR)
- Extended automotive temperature range (vs TL431BIDBZR)
- Cross-brand second sourcing (vs TL431BQDBZR-QR (Nexperia))
Design Notes
Always ensure at least 1 mA of continuous cathode current; below this threshold the TL431BQDBZR leaves regulation and output voltage drifts upward. In SMPS feedback designs, size the optocoupler LED series resistor so that LED current plus minimum bias stays above 1 mA at maximum duty. Also verify the REF pin leakage budget when using high-value dividers - keep divider current at least 100x the REF input bias for 0.5% accuracy.
The TL431 loop gain can oscillate when driving capacitive loads or optocouplers without compensation. Add a series resistor and capacitor (for example 1 k-ohm plus 0.1 uF) from cathode to REF to roll off the loop gain. TI's application sections on TL431 stability specify that output capacitors outside the stable region (roughly 1 uF to 10 uF for low ESR ceramics in some grades) can cause instability - check the datasheet stability graph for your cathode current.
Estimated: at VIN=24 V, VOUT regulation of 12 V with 50 mA cathode current, the series resistor dissipates about (24-12) V x 0.05 A = 0.6 W and the TL431 dissipates about 12 V x 0.05 A = 0.6 W. The SOT-23 package theta_JA of roughly 200-300 C/W allows only ~200 mW continuous at elevated ambient, so limit cathode current or move excess dissipation into the series resistor. Verify power against the package rating in the datasheet Absolute Maximum table.
Compliance Information
RoHS compliance and lead-free finish per standard TI SOT-23 DBZ production; the TL431BQDBZRQ1 variant is the AEC-Q100 qualified automotive option. REACH/halogen status not stated in provided data.
