The TL431A is a programmable precision shunt voltage regulator. It works like an adjustable Zener diode but with much better accuracy and stability.
It is widely used in:
Switched Mode Power Supplies (SMPS)
Battery chargers
Power adapters
Voltage regulation and feedback circuits
 
What It Does
The TL431A maintains a stable reference voltage of 2.5V between its Reference (REF) pin and Cathode (K). By using two external resistors, you can set any output voltage between 2.5V and 36V.
It is commonly used in feedback control with an optocoupler in power supplies.
 
Key Features
Adjustable output voltage: 2.5V – 36V
Internal reference voltage: 2.495V (very accurate)
Output current: Up to 100mA
High stability
Low temperature drift
 
Pin Configuration (TO-92 package)
If flat side faces you and pins downward:
REF (Reference)
Anode (A)
Cathode (K)
⚠️ Always verify with datasheet because some manufacturers may change pin order.
 
How It Works (Simple Explanation)
When voltage at REF reaches 2.5V, the device starts conducting.
It shunts current from Cathode to Anode to regulate voltage.
By adjusting resistor values, you control when it turns on.
 
Common Applications
SMPS feedback control
Adjustable voltage regulator
Over-voltage protection
Battery charging circuits
Precision reference circuits
 
TL431 vs Zener Diode
TL431A
Zener Diode
Adjustable
Fixed voltage
High accuracy
Less accurate
Stable
Less stable
Better for power supply feedback
Basic regulation