TL431BFDT - Adjustable Shunt Regulator 2.495-36V SOT-23 | Nexperia
Teilenummer: TL431BFDT ✓ Aktiv| Menge | Stückpreis | Gesamt |
|---|---|---|
| 1 | $0.28 | $0,28 |
| 10 | $0.22 | $2,20 |
| 100 | $0.14 | $14,00 |
| 500 | $0.11 | $55,00 |
| 1.000 | $0.08 | $80,00 |
TL431BFDT Übersicht
A shunt regulator (also called a shunt voltage reference) is a type of voltage regulator that maintains a set voltage across its terminals by sinking or sourcing current in parallel with the load. Unlike a series regulator, the shunt topology sits across the supply path and absorbs surplus current, making it the workhorse of the voltage reference family within power management and discrete semiconductor hierarchies. The TL431 is the industry-standard part of this class, widely used in isolated and non-isolated power supplies.
The TL431BFDT offers a tight B-grade reference tolerance of +/-0.5% at 25 C, an operating temperature range of -40 C to +125 C (Q-grade qualification per Nexperia automotive designation), and enhanced stability with a very low minimum load capacitance requirement in the FDT variant family. According to the Nexperia product page, the family covers reference tolerances from 2.0% down to 0.5% and temperature ranges up to 125 C, with AEC-Q100 qualification noted for automotive use.
Architecturally, the device integrates a 2.495 V bandgap reference, an error amplifier, and an open-collector output transistor. When the voltage at the REF pin exceeds the internal reference, the output transistor conducts cathode current, regulating the cathode voltage in closed-loop configurations such as optocoupler feedback in flyback converters.
Typical applications include secondary-side feedback regulation in AC-DC adapters and flyback SMPS, adjustable voltage references in battery chargers, overvoltage protection crowbars, and setpoint generation in LED drivers.
Design-wise, provide a minimum cathode bias current (about 1 mA) for regulation and add a small compensation capacitor at REF for loop stability in optocoupler feedback paths.
This page synthesizes verified distributor data, drop-in alternatives, pricing, and practical design notes not found in the manufacturer datasheet.
Drop-in-Alternativen für TL431BFDT – gleiches Gehäuse, Pin-kompatibel. Bauteile mit anderem Gehäuse, die eine PCB-Überarbeitung erfordern, sind ausgeschlossen.
Varianten dieser Serie
Modelle derselben Serie, die drop-in-kompatibel sind mit TL431BFDT (gleiche Bauform und Footprint) – abweichend in Package, Operating Temperature Range, Reference Voltage (Vref), Pinning Configuration, Product Type.
Schnellvergleichstool – Wählen Sie Alternativbauteile für den Direktvergleich:
TL431BMFDT,215
✅ Drop-In📋 Referenzalternative (nicht im Katalog)
TL431AFDT
✅ Drop-In📋 Referenzalternative (nicht im Katalog)
TL431QDBZR
✅ Drop-In✓ Auf Lager
$0.09 / Stück
Datenblatt ansehen →TL431BQDBZR
✅ Drop-In✓ Auf Lager
$0.07 / Stück
Datenblatt ansehen →TL431BQDBZRQ1
✅ Drop-In📋 Referenzalternative (nicht im Katalog)
TL431BFDT Technische Daten
| Ausgangstyp | Adjustable shunt |
| 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 |
| Temperature Coefficient | 888 ppm/C |
| Betriebstemperaturbereich | -40 C to +125 C |
| Gehäuse | SOT-23 (TO-236AB), 3-pin |
| Montageart | Surface Mount |
| Qualification | AEC-Q100 (automotive) |
| Pinning Configuration | Normal pinning (TL431xFDT family) |
| RoHS-Status | Compliant |
| Configuration | Three-terminal shunt regulator |
| Application Grade | Automotive / Industrial |
TL431BFDT Pin-Konfiguration
| Pin 1 | REF — Reference input - connect resistor divider from cathode; regulates when V(REF) = 2.495 V |
| Pin 2 | ANODE — Anode terminal - connect to circuit common / lowest potential |
| Pin 3 | CATHODE — Cathode terminal - output of the shunt regulator, sinks up to 100 mA |
Typische Anwendungen
TL431BFDT ist geeignet für 6 Anwendungs: Isolated AC-DC Flyback Feedback, Overvoltage Protection Crowbar, Battery Charger Voltage Regulation, Adjustable Voltage Reference for ADC and Precision Analog, LED Driver Current Regulation, Automotive Power Supply Supervision.
Isolated AC-DC Flyback Feedback
The TL431BFDT is the industry-standard error amplifier on the secondary side of isolated flyback and forward converters. Its 2.495 V reference drives a resistor divider from the regulated output (for example, a 5 V or 12 V rail), and its open-collector cathode sinks LED current in an optocoupler such as the PC817, closing the regulation loop to the primary-side PWM controller. The B-grade +/-0.5% reference tolerance directly translates into output-voltage accuracy of well under 1% after divider error, tighter than achievable with 1% or 2% grade parts. A small compensation network (typically an RC from cathode to REF) stabilizes the loop; the enhanced stability area of the FDT family with very low load-capacitance requirements simplifies this compensation. The -40 C to +125 C range and AEC-Q100 qualification support automotive charger designs.
Empfohlen
Overvoltage Protection Crowbar
In OVP circuits, the TL431BFDT monitors a supply rail through a resistor divider on its REF pin. When the rail exceeds the programmed trip point (Vref = 2.495 V threshold plus divider ratio), the device rapidly sinks cathode current, triggering an SCR gate or a MOSFET shutdown latch to protect downstream electronics. The B-grade +/-0.5% tolerance is critical here: with a 12 V rail, a 0.5% reference error shifts the trip point by only about 60 mV, whereas a 2% grade part could shift it by 240 mV - the difference between safe protection and nuisance tripping or inadequate protection margins. The 100 mA cathode current capability directly drives SCR gates without an intermediate transistor stage, and the SOT-23 package keeps the protection circuit compact on crowded protection PCB areas.
Empfohlen
Battery Charger Voltage Regulation
Precision battery chargers rely on accurate charge-termination voltages, making the TL431BFDT's +/-0.5% B-grade reference a natural fit. Placed as the feedback error amplifier on the charger's secondary regulation loop, it compares a divided battery voltage against the internal 2.495 V bandgap reference and controls the pass-element drive or PWM duty cycle. For a single-cell lithium-ion charger with a 4.2 V termination, a 0.5% reference error corresponds to only about 21 mV of termination uncertainty - significant because lithium cells charge-terminate within tight voltage windows for cycle life and safety. The -40 C to +125 C operating range supports automotive and industrial chargers, and the low 1 mA-class minimum cathode current keeps quiescent drain negligible in charger standby states, preserving battery shelf life.
Empfohlen
Adjustable Voltage Reference for ADC and Precision Analog
The TL431BFDT provides a low-cost adjustable reference source for ADC ratiometric measurements, comparator thresholds, and sensor excitation. Configured as a two-terminal shunt with a series resistor from the supply, it generates any setpoint between 2.495 V and 36 V. The 888 ppm/C temperature coefficient yields drift of roughly 12 mV over a 100 C swing at a 12 V setpoint - adequate for 10-bit and coarse 12-bit systems, though precision designs should budget this drift or use a higher-grade bandgap reference. The 100 mA capability can directly bias divider chains and LED indicators while still serving as a reference. In data-acquisition front ends using ADCs from the AD7xxx family, it sets mid-scale bias points and gain-network reference voltages where its 0.5% initial accuracy reduces calibration burden.
Empfohlen
LED Driver Current Regulation
Constant-current LED drivers use the TL431BFDT as a current-sense error amplifier: the REF pin monitors the voltage across a low-side sense resistor (setpoint = 2.495 V / Rsense), and the cathode controls a pass transistor or PWM dimming stage. With a 0.5% reference tolerance, LED current accuracy is set almost entirely by the sense resistor, typically achieving +/-1-2% total accuracy. For example, a 2.495 V threshold with a 5 ohm resistor regulates at roughly 500 mA of LED current. The 36 V cathode rating accommodates multi-LED string supplies directly, and the -40 C to +125 C range suits automotive daytime-running-light and industrial luminaire environments. The enhanced stability of the FDT family permits the small compensation capacitors needed to keep the dimming PWM loop stable at low duty cycles.
Empfohlen
Automotive Power Supply Supervision
Automotive ECUs and body-control modules use the TL431BFDT for rail supervision, load-dump clamping thresholds, and reference generation in fault-detection circuits. Its AEC-Q100 qualification and -40 C to +125 C range address under-hood and cabin module requirements, while the 0.5% B-grade accuracy ensures supervisory thresholds remain within specification over life and temperature - important for detecting overvoltage events such as jump-start or alternator-fault conditions on 12 V automotive rails. Typical circuits include undervoltage-lockout generation (REF divider on a clamped rail), watchdog reset thresholds, and precision bleed regulation in sensor excitation paths. The SOT-23 package minimizes board area in densely packed modules, and its low cost allows per-rail deployment across many supervision points rather than sharing one reference.
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Zusammenfassung der empfohlenen Produkte
Technische Referenzdaten für TL431BFDT – Vergleich, Designhinweise und Compliance-Informationen.
Auswahlhilfe
Vergleich mit Alternativen
| Parameter | Dieses Produkt | TL431BMFDT,215 | TL431AFDT | TL431QDBZR | TL431BQDBZR |
|---|---|---|---|---|---|
| Package | SOT-23 (TO-236AB) | SOT-23 (TO-236AB) - same | SOT-23 (TO-236AB) - same | SOT-23 (TO-236AB) - same | SOT-23 (DBZ) - same footprint |
| Brand | Nexperia | Nexperia | Nexperia | NXP Semiconductors | Texas Instruments |
| Reference Tolerance | +/-0.5% (B grade) | +/-0.5% (B grade) | +/-1.0% (A grade) | +/-2.0% (Q grade) | +/-0.5% (B grade) |
| Reference Voltage | 2.495 V | 2.495 V | 2.495 V | 2.495 V | 2.495 V |
| Max Cathode Voltage | 36 V | 36 V | 36 V | 36 V | 36 V |
| Max Cathode Current | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA |
| Operating Temperature | -40 C to +125 C | -40 C to +125 C | -40 C to +125 C | -40 C to +125 C | 0 C to +70 C / -40 C to +85 C / -40 C to +125 C grades |
| Automotive Qualification | AEC-Q100 | AEC-Q100 | AEC-Q100 | Automotive grade | Automotive (Q1 variant available) |
Wichtigste Unterscheidungsmerkmale
- B-grade 0.5% reference accuracy at commodity price (vs. TL431AFDT)
- Confirmed cross-brand drop-in compatibility (vs. TL431BQDBZR)
- Extended automotive temperature range with tight accuracy (vs. TL431QDBZR)
Designhinweise
The TL431BFDT requires a minimum cathode current (on the order of 1 mA for this family class) to stay in regulation; below this the reference becomes unspecified. Size the series resistor in shunt-reference applications so cathode current stays above the minimum at maximum output voltage and above it plus load demands across line and temperature. In optocoupler feedback designs, also verify the optocoupler LED forward current plus TL431 bias stays within the 100 mA cathode limit during startup transients, when the error amp saturates.
Loop stability in TL431-optocoupler feedback loops depends on the compensation network from cathode to REF (typically an RC series combination, e.g., around 1-10 kohm and 10-100 nF depending on loop gain) and on the optocoupler current-transfer ratio. The TL431xFDT family datasheet notes an enhanced stability area with very low load-capacitance requirement, but capacitance directly on REF above the stable region can degrade phase margin. Verify gain/phase margin with a bench Bode plot across load extremes before releasing the design.
Place the output-set divider resistors (R1/R2 from cathode and REF to anode) within a few millimeters of the REF pin and keep their traces away from switching-node copper to prevent injected ripple from modulating the reference threshold. Use 1% or better, low-TC (under 100 ppm/C) resistors so divider error does not erode the 0.5% reference accuracy. Connect the anode pin directly to a clean analog/signal common - not to power-ground carrying switch currents.
Compliance-Informationen
RoHS compliant per Nexperia standard product policy; AEC-Q100 automotive qualification noted in distributor product data (FindIC). REACH and halogen-free status not stated in provided data.
