TL431ACLPR - 2.495V Adjustable Shunt Reference 1% | TI
MPN: TL431ACLPR ✓ 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 |
TL431ACLPR Overview
A shunt voltage reference is a two- or three-terminal device that maintains a precise voltage across its terminals by sinking or sourcing current as needed. In the voltage-reference hierarchy, the TL431 sits under shunt regulator -> voltage reference -> power management IC, and unlike a series regulator it is placed in parallel with the load and regulates by controlling its own cathode current. Because it behaves like an error amplifier with an integrated 2.495 V bandgap reference and an open-collector output stage, it doubles as the feedback element in isolated and non-isolated switching power supplies.
Key features of the TL431ACLPR include the adjustable 2.495 V to 36 V output set with two external resistors, 1% accuracy for the A-grade device, up to 100 mA cathode sink current, 0.22 ohm typical output impedance, and operation over the 0C to +70C commercial temperature range. These parameters make it one of the most widely used references in the industry.
Technically, the TL431 combines a precision bandgap reference feeding the internal error amplifier; when the REF pin voltage exceeds 2.495 V, the output transistor conducts cathode current, closing the feedback loop. Its low dynamic output impedance and wide cathode current range (1 mA to 100 mA) allow stable regulation across varied bias conditions in optocoupler feedback paths.
Typical applications include secondary-side voltage feedback in flyback and forward SMPS designs driving an optocoupler, adjustable shunt regulation in adapters and chargers, and overvoltage protection comparators in industrial power rails.
A key design consideration: keep minimum cathode current at or above 1 mA to guarantee regulation, and add a small compensation capacitor in high-gain feedback loops to prevent oscillation.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for TL431ACLPR — 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 TL431ACLPR (same form factor and footprint) — differing in Adjustable Output Range, Operating Temperature Range, Output Type.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
TL431AILPR
✅ Drop-In📋 Reference alternative (not in catalog)
TL431CLPR
✅ Drop-In📋 Reference alternative (not in catalog)
TL431ILPR
✅ Drop-In✓ In Stock
$0.06 / Unit
View Datasheet →KA431
✅ Drop-In📋 Reference alternative (not in catalog)
AZ431
✅ Drop-In📋 Reference alternative (not in catalog)
LM431
✅ Drop-In📋 Reference alternative (not in catalog)
TL431ACLPR Maximum Ratings & Electrical Characteristics
| Output Type | Adjustable Shunt |
| Reference Voltage (Vref) | 2.495 V |
| Initial Accuracy | ±1% |
| Adjustable Output Range | 2.495 V to 36 V |
| Maximum Cathode Current | 100 mA |
| Minimum Cathode Current for Regulation | 1 mA |
| Output Impedance | 0.22 ohm (typical) |
| Maximum Cathode Voltage | 36 V |
| Operating Temperature Range | 0C to +70C |
| Package | TO-92-3 (LP) |
| Mounting Type | Through Hole |
| Packaging | Tape & Reel (R suffix) |
| RoHS Status | Compliant |
| Product Family | TL431 / TL432 Precision Programmable Reference |
TL431ACLPR Pin Configuration
| Pin 1 | REF — Adjustment pin, internally referenced to 2.495 V |
| Pin 2 | ANODE — Anode terminal, connected to ground reference |
| Pin 3 | CATHODE — Cathode terminal, sinks up to 100 mA when regulating |
Typical Applications
TL431ACLPR is suitable for 6 applications: SMPS Secondary-Side Feedback, AC Adapter and Charger Power Supplies, Overvoltage Protection and Crowbar Circuits, Adjustable Shunt Regulation in Industrial Power Rails, Precision Current Source and Sink Circuits, Comparator and Voltage Monitoring Functions.
SMPS Secondary-Side Feedback
The TL431ACLPR is the de facto standard error amplifier in isolated flyback and forward converter secondary sides. Placed across the 5 V or 12 V output with a resistor divider into its REF pin, it compares the sensed voltage against the internal 2.495 V reference and modulates the LED current of an optocoupler (e.g., via up to 100 mA sink capability), closing the isolated feedback loop to the primary PWM controller. Its ±1% accuracy directly sets output voltage tolerance, while the 0.22 ohm output impedance and wide 1 mA to 100 mA cathode range give designers flexibility in biasing. Compensation with an R-C network on the cathode-to-REF path sets loop bandwidth; a well-compensated TL431 loop routinely achieves 10 kHz-plus crossover in a 65 kHz flyback.
Recommended
AC Adapter and Charger Power Supplies
Phone chargers, laptop adapters, and low-cost wall warts almost universally use a TL431-type device for output regulation because it delivers precision regulation for pennies. In a 5 V USB charger, the divider ratio (VOUT = 2.495 V x (1 + R1/R2)) sets the exact output, and the A-grade ±1% tolerance of the TL431ACLPR keeps the regulated rail within tight USB voltage limits without trimming. The through-hole TO-92 package suits hand-inserted, cost-optimized adapter boards, and the 36 V maximum cathode voltage covers 5 V to 24 V output adapters alike. Designers must ensure at least 1 mA minimum cathode current through the divider and optocoupler chain at no load to keep the loop in regulation during light-load standby conditions.
Recommended
Overvoltage Protection and Crowbar Circuits
The TL431ACLPR functions as a precision threshold detector in overvoltage protection (OVP) schemes. When a divided sample of the protected rail exceeds the internal 2.495 V threshold, the cathode pulls toward the anode and sources gate drive into an SCR or drives a MOSFET, crowbarring the supply. The ±1% reference accuracy yields a protection threshold far tighter than a zener diode (typically ±5%), reducing false trips while guaranteeing protection margins. The 100 mA sink capability is ample for SCR gate triggering. Because the commercial-grade part is rated 0C to +70C, select the TL431AILPR for industrial environments. Place a small filter capacitor on the REF pin to reject transient spikes and prevent nuisance triggering from rail noise.
Recommended
Adjustable Shunt Regulation in Industrial Power Rails
In industrial control boards, the TL431ACLPR provides adjustable local regulation or clamping of auxiliary rails from 2.5 V to 36 V. Used as a shunt regulator with a series resistor from the rail, it sinks excess current to hold a precise node voltage for biasing sensors, comparators, or op-amp references. The low 0.22 ohm output impedance keeps the regulated node stiff under dynamic load steps, and the two-resistor programming means one board SKU can serve multiple rail voltages by changing divider values. For factory environments exceeding the 0C to +70C commercial range, drop in the pin-compatible TL431AILPR without PCB or BOM redesign. Verify dissipation in the shunt resistor, which dominates the thermal budget rather than the IC itself.
Recommended
Precision Current Source and Sink Circuits
By forcing the REF pin with a current-sense resistor voltage, the TL431ACLPR closes a feedback loop that regulates current rather than voltage, forming a simple two-terminal precision current source or sink. The ±1% reference accuracy translates directly to ±1% current accuracy, far better than BJT Vbe-based solutions which drift several mV per degree C. This topology is common in LED bias, sensor excitation, and 4-20 mA loop transmitters, where the 36 V cathode rating covers 24 V industrial loops. Keep the cathode current between 1 mA and 100 mA and budget loop headroom accordingly. For sub-2.5 V sense thresholds, consider the TLV431 with its 1.24 V reference instead of reducing the sense resistor to impractically low values.
Recommended
Comparator and Voltage Monitoring Functions
The TL431ACLPR doubles as a comparator with a built-in 2.495 V reference: when the REF pin exceeds the threshold, the open-collector-style cathode output pulls low, sinking up to 100 mA - enough to drive a relay, LED indicator, or logic input directly. This makes it an economical solution for battery-low indicators, supply-rail supervision, and window comparators when paired with a second TL431 for the opposite threshold. Response is fast for an analog device, and the ±1% accuracy gives repeatable trip points board to board. Note the behavior flagged by designers on forums: below threshold the cathode can still sit low, so for sharp cut-off behavior add hysteresis with a feedback resistor from cathode to REF and verify thresholds across temperature.
Recommended
Recommended Products Summary
Engineering reference data for TL431ACLPR — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | TL431AILPR | TL431CLPR | KA431 | AZ431 |
|---|---|---|---|---|---|
| Package | TO-92-3 (LP) | TO-92-3 (LP) - same | TO-92-3 (LP) - same | TO-92-3 - same footprint | TO-92-3 - same footprint |
| Brand | Texas Instruments | Texas Instruments | Texas Instruments | onsemi | Diodes Incorporated |
| Reference Voltage | 2.495 V | 2.495 V | 2.495 V | 2.495 V | 2.5 V-class |
| Max Cathode Current | 100 mA | 100 mA | 100 mA | 100 mA | 100 mA |
| Max Cathode Voltage | 36 V | 36 V | 36 V | 36 V | 36 V |
Key Differentiators
- ±1% A-grade accuracy (vs TL431CLPR)
- Industry-standard cross-reference footprint (vs KA431)
- Cost trade-off vs temperature range (vs TL431AILPR)
Design Notes
Never substitute a TL432 for a TL431 in an existing PCB: the two family members share electrical specifications but have different TO-92 pin orders, so a direct swap reverses REF and ANODE functions and can destroy the part or the supply. Always check the grade suffix (C = 0C to +70C, I = -40C to +85C) when second-sourcing - the A in TL431ACLPR denotes ±1% accuracy, not temperature grade.
Guarantee at least 1 mA of cathode current under all operating conditions, including no-load standby; below this the device exits regulation and the output drifts high. Estimated: in a 5 V charger feedback path with a 1 k ohm series resistor from a 5 V output, the cathode pulls to ~2.5 V, giving roughly 2.5 mA - adequate margin. Size the divider current (~0.5-1 mA through R1/R2) so total sink demand stays under the 100 mA maximum.
In optocoupler feedback loops, compensation is essential: a series R-C from cathode to REF (with an optional capacitor from REF to anode) sets the loop zero and prevents oscillation caused by the optocoupler CTR pole. Follow the stability regions in the TI TL431/TL432 datasheet for acceptable cathode capacitance - direct capacitive loads in the nF range on the cathode can destabilize the device in linear shunt-regulator use.
The TL431ACLPR itself dissipates V(ka) x I(ka); estimated at 36 V cathode and 100 mA sink that is 3.6 W, far beyond TO-92 capability without derating. In practice, the series dropper resistor takes most of the voltage. Calculate resistor power separately and confirm the IC stays within its package dissipation limit at maximum ambient, using the derating curves in the manufacturer datasheet.
Compliance Information
RoHS compliance and lead-free finish per TI product listings; REACH, halogen-free, and conflict-minerals status not stated in the provided data.
