TL431QDBZR - 36V Adjustable Shunt Voltage Reference | TI
MPN: TL431QDBZR ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.29 | $0.29 |
| 10 | $0.23 | $2.30 |
| 100 | $0.14 | $14.00 |
| 500 | $0.11 | $55.00 |
| 1,000 | $0.09 | $90.00 |
TL431QDBZR Overview
A shunt voltage reference is a type of voltage reference IC that regulates voltage by shunting (bypassing) excess current to ground through an internal transistor, placed in parallel with the load. Within the power management hierarchy, it sits under voltage references alongside series references, and is widely used as an error amplifier and feedback element in isolated and non-isolated power supplies.
Key features include a programmable output voltage set from Vref (2.495V) up to the 36V maximum cathode voltage using just two external resistors, a low dynamic output impedance of approximately 0.22 ohm (typical), a sharp low-current turn-on characteristic, and operation across the -40C to +125C automotive-relevant Q temperature grade.
The TL431 integrates a 2.495V bandgap reference and an internal output driver, effectively functioning as a single-supply error amplifier with an open-collector-style cathode output. This architecture allows it to compare a divided-down feedback voltage against its internal reference and directly drive an optocoupler LED in isolated flyback converters, eliminating a separate op-amp.
Typical applications include adjustable shunt regulation in AC-DC adapters, secondary-side feedback regulation in isolated flyback and forward SMPS designs, overvoltage protection crowbar circuits, and setpoint control in LED drivers and battery chargers.
A key design consideration: the device requires a minimum cathode current of roughly 1 mA to maintain regulation, so the resistive divider and bias network must guarantee this minimum under worst-case load conditions.
This page synthesizes distributor pricing, verified drop-in alternatives across multiple manufacturers, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for TL431QDBZR — 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 TL431QDBZR (same form factor and footprint) — differing in Package, Operating Temperature Range, Minimum Cathode Current for Regulation, Adjustable Output Range, Automotive Qualification.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
TL431AQDBZR
✅ Drop-In✓ In Stock
$0.09 / Unit
View Datasheet →TL431BQDBZR
✅ Drop-In ⚠️ Specs Unverified✓ In Stock
$0.07 / Unit
View Datasheet →TL431QDBZT
✅ Drop-In📋 Reference alternative (not in catalog)
TL431QDBZR,215
✅ Drop-In📋 Reference alternative (not in catalog)
KA431
✅ Drop-In📋 Reference alternative (not in catalog)
AZ431
✅ Drop-In📋 Reference alternative (not in catalog)
LM431
✅ Drop-In📋 Reference alternative (not in catalog)
TL431QDBZR Maximum Ratings & Electrical Characteristics
| Product Type | Adjustable Precision Shunt Voltage Reference |
| Reference Voltage (Vref) | 2.495 V |
| Output Tolerance | ±2.2% (Q grade, 25C) |
| Adjustable Output Range | Vref (2.495 V) to 36 V |
| Maximum Cathode Current | 100 mA |
| Maximum Cathode Voltage | 36 V |
| Minimum Cathode Current for Regulation | 1 mA (typical) |
| Dynamic Output Impedance | 0.22 ohm (typical) |
| Operating Temperature Range | -40C to +125C (Q grade) |
| Package | SOT-23-3 (DBZ, TO-236AB) |
| Mounting Type | Surface Mount |
| Package Dimensions | 2.9 mm x 1.3 mm x 1 mm body |
| Terminal Pitch | 1.9 mm |
TL431QDBZR Pin Configuration
| Pin 1 | REF — Reference input - output voltage setpoint, 2.495V nominal threshold |
| Pin 2 | ANODE — Anode - common terminal, connected to system ground |
| Pin 3 | CATHODE — Cathode - shunt output, sinks current up to 100 mA, rated to 36V |
Typical Applications
TL431QDBZR is suitable for 6 applications: Isolated Flyback Converter Feedback, Adjustable Shunt Voltage Regulation, Overvoltage Protection Crowbar, LED Driver Current Regulation, Battery Charger Setpoint Control, Precision Comparator / Threshold Detector.
Isolated Flyback Converter Feedback
The TL431QDBZR is the industry-standard secondary-side error amplifier in isolated flyback and forward AC-DC converters. Its 2.495V reference compares the divided-down output voltage while the cathode sinks current from an optocoupler LED (e.g., PC817), closing the isolation barrier loop. The ±2.2% Q-grade tolerance supports typical 5% output accuracy targets once divider tolerance is budgeted, and its ability to sink up to 100 mA comfortably drives the optocoupler LED set resistor (typically 1-5 mA LED current). Compensation networks (RC across cathode-ref) stabilize the loop; the low dynamic impedance of 0.22 ohm typical keeps the gain stage clean across the -40C to +125C range.
Recommended
Adjustable Shunt Voltage Regulation
In its basic role, the TL431QDBZR regulates a supply rail from 2.495V up to 36V using only two resistors, providing a low-cost precision shunt regulator for low-power rails. With equal divider resistors it regulates at ~4.99V; scaling the divider yields any target within range. The SOT-23 package dissipates safely up to a few hundred milliwatts - for example, 10 mA at 12V is 120 mW. The device requires a minimum 1 mA cathode current to maintain regulation, so the source impedance must guarantee this at worst case. Compared to Zener diodes, it offers far sharper knee, lower dynamic impedance (0.22 ohm typical), and programmable voltage.
Recommended
Overvoltage Protection Crowbar
The TL431QDBZR makes an excellent overvoltage detector in crowbar circuits: its REF pin monitors a divided-down supply, and when the rail exceeds the setpoint the cathode pulls low, triggering an SCR gate or a fuse-breaking element. The sharp turn-on characteristic near 2.495V on REF gives a crisp threshold, while the Q temperature grade keeps the trip point stable from -40C to +125C. Threshold accuracy is bounded by the ±2.2% reference tolerance plus divider error - use the TL431AQDBZR (±1%) for tighter protection windows. This topology is common in automotive and industrial supplies where a latched shutdown on overvoltage protects downstream electronics.
Recommended
LED Driver Current Regulation
The TL431QDBZR regulates LED current by sensing voltage across a low-side current-sense resistor: when the drop reaches 2.495V, the device shunts excess drive, holding current constant. This topology gives a precise, temperature-stable current setpoint at low cost - for example, a 2.49-ohm sense resistor sets ~100 mA. The wide 36V cathode rating supports strings of LEDs on higher-voltage rails, and the SOT-23 footprint suits LED bulb and fixture PCBs. Designers must budget the ±2.2% reference tolerance into the current accuracy target and ensure minimum cathode bias current for regulation at low line conditions.
Recommended
Battery Charger Setpoint Control
In linear and switch-mode battery chargers, the TL431QDBZR provides the precision voltage setpoint that terminates charge or regulates float voltage. The adjustable output from 2.495V to 36V covers single-cell Li-ion (4.2V) through multi-cell lead-acid (up to 36V systems) with a simple divider. The Q-grade -40C to +125C operation supports automotive and outdoor charging environments. Because charge accuracy directly affects battery life and safety, many designers select the TL431AQDBZR or TL431BQDBZR grade (±1% / ±0.5%) in this application; the same DBZ footprint makes upgrading a zero-rework change.
Recommended
Precision Comparator / Threshold Detector
Thanks to its internal 2.495V reference and high-gain input, the TL431QDBZR doubles as a single-supply comparator with an open-collector-style output: the cathode saturates low when REF exceeds 2.495V and stays high otherwise. This makes it a compact undervoltage/overvoltage detector, window monitor, or level shifter without a separate op-amp and reference IC. Designers should note the gain is optimized for regulation rather than speed, so response is in the microsecond range - adequate for supervisory and protection duties but not fast signal comparison. The 3-pin SOT-23 minimizes board area in these monitoring roles.
Recommended
Recommended Products Summary
Engineering reference data for TL431QDBZR — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | TL431AQDBZR | TL431BQDBZR | TL431QDBZR,215 | KA431 |
|---|---|---|---|---|---|
| Package | SOT-23-3 (DBZ) | SOT-23-3 (DBZ) - same | SOT-23-3 (DBZ) - same | SOT-23 (TO-236AB) - same | SOT-23 - same |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | Nexperia | onsemi |
| Reference Tolerance | ±2.2% | ±1% | ±0.5% | ±2% | grade-dependent (typically ±2%) |
| Reference Voltage | 2.495 V | 2.495 V | 2.495 V | 2.495 V | ~2.495 V |
| Max Cathode Current | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA |
Key Differentiators
- Cost-effective Q-grade with wide temperature range (vs TL431AQDBZR)
- Tighter tolerance available at identical footprint (vs TL431BQDBZR)
- Second-source flexibility (vs TL431QDBZR,215)
Design Notes
Ensure a minimum cathode current of about 1 mA under worst-case conditions (minimum input voltage, maximum divider impedance). Below this threshold the TL431QDBZR leaves its regulated region and output impedance rises sharply, degrading load regulation. A common fix is adding a resistor from cathode to supply to guarantee bias independent of the load path. Also never omit a compensation network (series RC from cathode to REF, typically 100 ohm-1 kohm plus 0.1-10 uF) in feedback loops - the device has a pole that can destabilize optocoupler loops.
Estimated: power dissipation in the SOT-23 (DBZ) package equals (Vcathode - Vanode) x Icathode. For example, shunting 10 mA at 12V dissipates 120 mW, and 20 mA at 24V dissipates 480 mW - approaching SOT-23 limits. Keep dissipation below roughly 300-350 mW without dedicated copper pour, and verify junction temperature against the -40C to +125C operating range using package theta-JA from the datasheet thermal table.
Place the REF pin divider resistors close to the IC and route the sense trace away from switching nodes to avoid injecting flyback ripple into the reference point. Kelvin-connect the divider directly to the regulated output node, not to a shared high-current trace, or divider IR drops will shift the regulation setpoint. Use 1% resistors (or better for A/B-grade parts) so divider error does not dominate the ±2.2% reference tolerance.
Compliance Information
Compliance data not present in the verified web data for this part; confirm RoHS/REACH status on the TI product page.
