TL431A – Adjustable Precision Shunt Regulator

Description

🔋 TL431A – Adjustable Precision Shunt Regulator

(Programmable Zener Diode Replacement)

📌 General Description

The TL431A is a three-terminal adjustable shunt regulator that can be programmed to regulate voltages from 2.495V to 36V with high accuracy. It behaves like an adjustable Zener diode with a reference input, allowing precise control in linear and switching power supplies, battery chargers, and control loops.

The “A” version has higher accuracy compared to the standard TL431.

⚙️ Key Specifications

🔌 Pinout (TO-92 / SOT-23)

TO-92 Package:

        _______
       |       |
REF  --|  1   |-- 3  Cathode (K)
ANODE --|__2__|-- 

🧪 Key Features

• Programmable voltage reference (2.5–36V)
• Precise internal reference (2.495V)
• Replaces Zener diodes in many applications
• Low dynamic impedance
• High temperature stability
• Works in open-loop or closed-loop systems

🛠️ Typical Applications

• Switching and linear power supplies
• Adjustable voltage regulators
• Battery chargers
• Overvoltage / undervoltage protection
• Feedback control for optocoupler isolation
• Precision current limiters

🔄 How It Works

The TL431 behaves like a Zener diode with a reference input:

• When the voltage at REF reaches 2.495V, the device starts to conduct between cathode and anode (like a Zener).
• You can set an adjustable output voltage with a voltage divider:

VOUT=VREF(1+R1R2)V_{OUT} = V_{REF} \left(1 + \frac{R1}{R2} \right)

(Where R1 is connected from VOUT to REF, and R2 from REF to ground.)

🧯 Advantages

• More accurate than regular Zener diodes
• Easy to configure for different output voltages
• High thermal and electrical stability
• Works as precision shunt regulator

⚠️ Limitations

• Requires external resistors for voltage adjustment
• Needs minimum 1 mA cathode current to regulate
• Not ideal for ultra-low power applications