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TL431 SOT-23 Adjustable Precision Shunt Voltage Reference IC 2.5V–36V (20-Pack)
TL431 SOT-23 Adjustable Precision Shunt Voltage Reference IC 2.5V–36V (20-Pack)
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TL431 SOT-23 Adjustable Precision Shunt Voltage Reference IC — 2.5V–36V (20-Pack)
The TL431 is a three-terminal adjustable shunt voltage reference in a compact SOT-23 surface-mount package. With a reference voltage of 2.495V (adjustable up to 36V via external resistors), 0.5% initial accuracy, and operation from 1mA to 100mA, it is the most widely used precision reference IC in SMPS optocoupler feedback loops, voltage monitors, and precision reference circuits.
Key Specifications
| Parameter | Value |
|---|---|
| Part Number | TL431 / TL431A |
| Package | SOT-23 (SMD) |
| Reference Voltage (VREF) | 2.495V (internal, ±0.5% for TL431A) |
| Adjustable Output Range | 2.5V – 36V (via R1/R2 divider) |
| Cathode Current Range | 1mA – 100mA |
| Temperature Coefficient | ~50ppm/°C typical |
| Dynamic Impedance | 0.22Ω typical |
| Operating Temperature | 0°C to +70°C (TL431) / −40°C to +85°C (TL431A) |
| Quantity | 20 pieces |
Output Voltage Setting Formula
VOUT = VREF × (1 + R1/R2) = 2.495 × (1 + R1/R2)
| Target VOUT | R1 (kohm) | R2 (kohm) |
|---|---|---|
| 2.5V | 0 (short) | Any |
| 5.0V | 10k | 10k |
| 12.0V | 38k | 10k |
| 15.0V | 50k | 10k |
Why Choose TL431?
- 0.5% Accuracy (TL431A) — Precise reference for SMPS feedback and ADC reference applications
- Adjustable 2.5V–36V — Two resistors set any output voltage in range
- Low Dynamic Impedance — 0.22Ω provides stable reference under varying load current
- SOT-23 Package — Minimal PCB footprint for compact SMPS and charger designs
- Industry Standard — Used in virtually every SMPS feedback loop; extensive reference designs available
Typical Applications
- SMPS optocoupler feedback loop (flyback, forward converter output regulation)
- Precision voltage reference for ADC and DAC circuits
- Overvoltage protection threshold detector
- Battery voltage monitor and low-battery alarm
- Linear regulator replacement (shunt regulator)
- LED constant-current driver reference
SMPS Feedback Circuit
TL431 REF pin connects to R1/R2 voltage divider from VOUT. Cathode connects to optocoupler LED anode via series resistor. Anode to GND. When VOUT rises above setpoint, TL431 conducts more current through optocoupler, reducing PWM duty cycle to regulate output.
FAQ
Q: What is the difference between TL431 and TL431A?
A: TL431A has tighter initial accuracy (±0.5% vs ±2% for standard TL431) and lower temperature coefficient. Use TL431A for precision applications; standard TL431 for general SMPS feedback.
Q: Can TL431 replace a zener diode?
A: Yes — TL431 is a programmable zener with much tighter tolerance and lower dynamic impedance than standard zener diodes. It is the preferred choice for precision voltage clamping.
Package Contents
- 20× TL431 SOT-23 Adjustable Shunt Voltage Reference IC
