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TL431AILPR

Shunt Ref, 2.495V, 1% Acc, Adj to 36V, TO-92

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Manufacturer Part：

TL431AILPR

Package：

TO-92 (4.5 x 4.1 mm, 2.54mm pitch, through-hole)

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Description

Product Overview

The TL431AILPR from Texas Instruments is a precision programmable shunt voltage reference with 1% initial accuracy, adjustable output from Vref to 36V, and TO-92 through-hole package.

Key Specifications

Type Precision Programmable Shunt Regulator / Reference
Reference Voltage (Vref) 2.495V (typical), 1% tolerance (A grade)
Adjustable Output Vref (2.495V) to 36V
Cathode Current Range 1 mA to 100 mA
Output Impedance 0.2 Ohm (typical)
Reference Input Current 2 uA (typical)
Temperature Drift 14 mV (typical, I temp range)
Dynamic Impedance 0.2 Ohm @ IKA=1-100mA, f<=1kHz
Package TO-92 (LP, 3-pin through-hole)
Operating Temperature -40C to +85C (I grade)

Features

  • 1% initial voltage tolerance (A grade) at 25C
  • Adjustable output voltage from 2.495V to 36V with two resistors
  • 0.2 Ohm typical dynamic output impedance
  • 1mA to 100mA sink current capability
  • Low reference input current: 2uA typical
  • Sharp turn-on characteristic for Zener replacement
  • -40C to +85C operation (I grade)

Applications

  • Switching power supply error amplifier
  • Adjustable voltage reference
  • Zener diode replacement
  • Voltage monitoring / comparator with reference
  • Secondary-side regulation in flyback SMPS

The TL431AILPR from Texas Instruments is the industry-standard precision programmable shunt voltage reference in a TO-92 through-hole package. The A grade provides 1% initial reference voltage tolerance at 25C, making it suitable for precision power supply regulation. The I suffix indicates the industrial temperature range of -40C to +85C. The LP suffix denotes the TO-92 3-pin package, and R indicates tape and reel packaging (ammo pack). The TL431 functions as a three-terminal adjustable shunt regulator: the output voltage can be set to any value between Vref (approximately 2.495V) and 36V using two external resistors. The internal 2.495V bandgap reference and error amplifier compare the REF pin voltage with the internal reference and drive the open-collector output to sink current, regulating the cathode voltage. The 0.2 Ohm typical dynamic output impedance provides excellent load regulation. The 1mA minimum cathode current ensures the internal reference and error amplifier are active, while the 100mA maximum allows direct drive of optocoupler LEDs in isolated power supply feedback loops.

The TL431AILPR contains an internal 2.495V bandgap reference voltage source and a high-gain error amplifier with an open-collector NPN output transistor. The REF pin connects to the non-inverting input of the error amplifier, while the internal 2.495V reference connects to the inverting input. When the voltage at the REF pin exceeds the internal 2.495V reference, the error amplifier drives the output NPN transistor to sink more cathode current, pulling the cathode voltage lower. When the REF pin voltage is below the reference, the error amplifier reduces the cathode current, allowing the cathode voltage to rise. In the typical shunt regulator configuration, two resistors R1 and R2 form a voltage divider from the cathode to ground, with the midpoint connected to the REF pin. The output voltage is VOUT = Vref x (1 + R1/R2) + Iref x R1, where Iref is typically 2uA and can be neglected for R1 values below 10kOhm. For example, R1 = R2 = 10kOhm gives VOUT = 2 x 2.495V = 4.99V. In switching power supply applications, the TL431 is typically used with an optocoupler (e.g., PC817) on the secondary side: the TL431 compares a fraction of the output voltage with its internal reference and drives the optocoupler LED, providing isolated feedback to the primary-side PWM controller.

Pin Name Type Function
1 REF Input Reference input (compared with internal 2.495V)
2 Anode Power Ground / common (normally connected to GND)
3 Cathode I/O Shunt current output / voltage input
  • 5V flyback SMPS secondary-side error amplifier with TL431 and PC817 optocoupler providing 1% output voltage regulation
  • Adjustable 2.5V to 30V precision voltage reference with two external resistors and 0.2 Ohm output impedance
  • Over-voltage comparator with 2.495V threshold and 100mA cathode sink current for crowbar protection
Manufacturer Part Number Package Notes
TI TL431BLPR TO-92 0.5% tolerance (B grade)
TI TL431AIDBZR SOT-23-3 SMD version, same function
onsemi TL431AILPRAG TO-92 Direct equivalent
ST TL431AILPRM TO-92 Direct equivalent
TI TLA431AIDBZR SOT-23-3 All-capacitor stable version
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