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TL431Adjustable shunt regulator
A precise reference. A controlled path to ground.
TL431 is a three-terminal adjustable shunt regulator. It compares its REF input with an internal reference and sinks current from cathode to anode to hold a resistor-selected voltage. Unlike a series regulator, it needs an external feed resistor or another controlled current source. Two feedback resistors set an output from approximately 2.495 V up to 36 V. The supply resistor must provide enough current for the load, divider and regulator at the lowest input voltage, while respecting dissipation at the highest input. This page selects TI’s standard-accuracy TL431C in TO-92 and SOT-23-3, rated from 0°C to 70°C. Their physical pin numbers differ. A and B accuracy grades, wider temperature grades and the differently pinned TL432 must be checked by their exact ordering codes.
Cathode / shunt pathAnode / commonReference input
TL431CLPTO-92Bottom view · flat edge below · 3 REF, 2 A, 1 K
TL431CDBZRSOT-23-3Top view · 1 K, 2 REF, 3 A
Click a lead or use the arrow keys. Bottom view · flat edge below · 3 REF, 2 A, 1 K
PIN 1 · Cathode / shunt path
Cathode / shunt nodeK
Function
The regulator sinks current from the cathode to the anode to control this voltage.
How to connect
Feed through a current-limiting series resistor; connect the upper feedback resistor here.
Electrical note
Do not connect directly across an unrestricted supply. Recommended cathode current is 1–100 mA.
PIN 2 · Anode / common
Anode / reference returnA
Function
Common reference for the internal amplifier and cathode voltage.
How to connect
Connect to the circuit ground and the lower divider resistor.
Electrical note
TO-92 physical pin 2; SOT-23 physical pin 3.
PIN 3 · Reference input
Reference inputREF
Function
Compares the external divider node against approximately 2.495 V relative to the anode.
How to connect
Connect to the junction of the two output-setting resistors.
Electrical note
TO-92 physical pin 3; SOT-23 physical pin 2. Reference-input current slightly raises the nominal setpoint.
At a glance
Adjustable shunt regulator
A series resistor feeds the output. The load takes its share, while the TL431 adjusts cathode current to hold the divider near its reference.
2.495 VNominal reference
1–100 mA · recommendedCathode range
±2 % · standard gradeInitial tolerance
0–70 °C · TL431CAmbient range
Operating profile
TL431CLP
Operating envelope
Key parameters and their test conditions
- Cathode voltage
- VREF to 36 VConditions / notes: Referenced to the anode
- Cathode current
- 1–100 mAConditions / notes: Recommended range; power dissipation may impose a lower maximum
- Ambient temperature
- 0–70°CConditions / notes: Selected commercial C grade
- Initial accuracy
- ±2% at 25°CConditions / notes: A: ±1%; B: ±0.5% are different grades
- Selected through-hole part
- TL431CLPConditions / notes: Bulk straight-lead TO-92
- Selected SMD part
- TL431CDBZRConditions / notes: SOT-23-3; different physical pin map
Package details
Follows the selected physical package
- Manufacturer
- Texas Instruments
- Part number
- TL431CLP
- Package
- TO-92
- Connections
- 3 pins
- Mounting
- Through-hole
- Lead pitch
- 1.27 mm · straight leads
- Package code
- LP
- Thermal reference
- Package, board copper and cathode dissipation determine junction temperature
Connections by function
Select a pin to open its function, electrical notes and wiring guidance.
Reference input1 pins
Anode / common1 pins
Cathode / shunt path1 pins
Cathode / shunt path1 pins
Reference input1 pins
Anode / common1 pins
Limit the feed current
A 680 Ω resistor feeds the output from 12 V. It must cover load, divider and cathode currents.
Sense the divided output
Two 10 kΩ resistors place about 2.495 V at REF when the output is near 5 V.
Sink the remainder
The internal amplifier adjusts current from K to A. The output falls out of regulation if the load leaves too little cathode current.
For equal 10 kΩ divider resistors, 2.495 × 2 gives 4.990 V; 2 µA typical reference current adds 0.020 V. The resulting 5.01 V is illustrative, not a precision guarantee.
Pin reference
Select a pin to explore its function and connection.
3 pins
| Pin | Signal | Type | Function |
|---|---|---|---|
| K | Cathode / shunt node | The regulator sinks current from the cathode to the anode to control this voltage. | |
| A | Anode / reference return | Common reference for the internal amplifier and cathode voltage. | |
| REF | Reference input | Compares the external divider node against approximately 2.495 V relative to the anode. |
No pins match. Try a signal name or choose All pins.
Operating envelope
TI TL431C standard-accuracy grade
Manufacturer specifications 6 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Cathode voltage | VREF to 36 V | Referenced to the anode |
| Cathode current | 1–100 mA | Recommended range; power dissipation may impose a lower maximum |
| Ambient temperature | 0–70°C | Selected commercial C grade |
| Initial accuracy | ±2% at 25°C | A: ±1%; B: ±0.5% are different grades |
| Selected through-hole part | TL431CLP | Bulk straight-lead TO-92 |
| Selected SMD part | TL431CDBZR | SOT-23-3; different physical pin map |
No specifications match. Try a parameter name or a unit.
A shunt-current rating is not a load-current rating.
Reference and regulation
Electrical-characteristic test conditions
Manufacturer specifications 6 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Reference at 25°C | 2.440 / 2.495 / 2.550 V | Minimum / typical / maximum; VKA = VREF, IKA = 10 mA |
| Reference current | 2 µA typical; 4 µA maximum | IKA = 10 mA; R1 = 10 kΩ, R2 open |
| Minimum regulation current | 0.4 mA typical; 1 mA maximum | Do not design only around the typical value |
| Dynamic impedance | 0.2 Ω typical; 0.5 Ω maximum | f ≤ 1 kHz; IKA = 1–100 mA; VKA = VREF |
| Off-state cathode current | 0.1 µA typical; 1 µA maximum | VKA = 36 V; VREF input = 0 V |
| Output setting | VOUT ≈ VREF × (1 + RUP/RLOW) + IREF × RUP | Resistor tolerance and device errors remain |
No specifications match. Try a parameter name or a unit.
Initial tolerance, drift, loading and divider errors all contribute to real output accuracy.
Temperature and grade distinctions
Do not merge limits from different packages
Manufacturer specifications 6 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| C-grade ambient | 0 to +70°C | The two orderables shown here |
| I-grade ambient | −40 to +85°C | Requires an I-grade orderable |
| Q-grade ambient | −40 to +125°C | Requires a Q-grade orderable |
| C reference change: TO-92 | 4 mV typical; 25 mV maximum | VKA = VREF; IKA = 10 mA; over C ambient range |
| C reference change: SOT-23-3 | 6 mV typical; 16 mV maximum | Different package-specific limits in the same table |
| Thermal check | TJ ≈ TA + P × θJA | Use the exact package and PCB thermal conditions |
No specifications match. Try a parameter name or a unit.
Temperature drift does not replace the initial reference-voltage tolerance.
A nominal 5 V shunt supply
12 V input · SOT-23-3 physical circuit
Manufacturer specifications 6 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Feed resistor | 680 Ω, at least 0.25 W | 12 V to K1 / output node |
| Upper divider resistor | 10 kΩ | K1 to REF2 |
| Lower divider resistor | 10 kΩ | REF2 to A3 / GND |
| Example load | 1 kΩ | Output to GND; approximately 5 mA |
| Anode | Pin 3 to GND | The TO-92 equivalent is pin 2 |
| Output capacitor | None in this teaching circuit | Capacitive-load stability must be checked before adding one |
No specifications match. Try a parameter name or a unit.
The diagram is a low-voltage teaching circuit, not a mains-connected power supply.
Follow the current budget
Illustrative typical-value arithmetic
Manufacturer specifications 7 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Ideal divider output | 4.990 V | 2.495 × (1 + 10/10) |
| Reference-current correction | +0.020 V | 2 µA × 10 kΩ |
| Illustrative output | 5.010 V | Before tolerances, temperature and load errors |
| Feed current | 10.279 mA | (12 − 5.01) / 680 |
| Load / upper-divider currents | 5.010 mA / 0.2515 mA | 1 kΩ load; lower-divider current plus 2 µA |
| Remaining cathode current | Approximately 5.018 mA | Feed minus load minus upper-divider current |
| Feed resistor / TL431 power | 71.9 mW / 25.1 mW | Nominal arithmetic; include worst-case input/load margins |
No specifications match. Try a parameter name or a unit.
These are calculations, not live readings or an electrical simulation.
Physical pin correspondence
Check orientation before connecting
Manufacturer specifications 6 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Cathode K | TO-92: 1 · SOT-23: 1 | Controlled shunt/output node |
| Anode A | TO-92: 2 · SOT-23: 3 | Common return |
| Reference REF | TO-92: 3 · SOT-23: 2 | Divider sense input |
| TO-92 pinout picture | Bottom view, flat edge below | Left-to-right: 3 REF, 2 A, 1 K; top-side PCB view is mirrored |
| SOT-23 pinout picture | Top view | K1 upper left, REF2 lower left, A3 at right |
| TL432 | Same function; different small-package pinouts | Do not substitute by name alone |
No specifications match. Try a parameter name or a unit.
The straight-lead TO-92 footprint is not the wider formed-lead footprint.
Stability and absolute limits
Stress limits are not operating targets
Manufacturer specifications 6 parameters
| Parameter | Value | Conditions / notes |
|---|---|---|
| Cathode absolute voltage | 37 V | Recommended maximum remains 36 V |
| Cathode absolute current | −100 to +150 mA | Do not use as a normal operating range |
| Reference absolute current | −0.05 to +10 mA | Input stress limit |
| Junction / storage | 150°C / −65 to +150°C | Absolute limits |
| Capacitive load | Can destabilize the shunt loop | Check the manufacturer stability curves for voltage, current and capacitance |
| Worst-case power | VKA × IKA | Evaluate high input / light load, not only the nominal circuit |
No specifications match. Try a parameter name or a unit.
Allow electrical and thermal margin, and verify stability in the actual circuit.
Adjustable references
Set a voltage with two resistors and a suitable feed-current budget.
Manufacturer application guideIsolated supply feedback
Control an optocoupler LED in a properly compensated feedback circuit.
Manufacturer application guideVoltage thresholds
Use the reference and cathode response for a threshold detector with suitable loading.
Manufacturer application guideTake it into ProTech
Find TL431 in the Components Library to place its schematic symbol and connect its pins.
Reference page · circuit simulation model not yet availableOpen ProTech