TL431, Programmable Reference Voltage, 2.495V

The TL431 is a programmable shunt regulator which can provide both positive and negative reference voltages. It is a Zener diode whose voltage rating can be adjusted based on the value of resistors connected to the reference pin. It is commonly used as a low cost reference voltage provider in isolated power supply circuits.

From the internal circuit diagram of the IC shown above we can notice that it consists of a NPN transistor with an op-amp that has a precise voltage of 2.5V on the non-inverting terminal.  The collector and emitter pin of the transistor forms the cathode and the anode terminal of the IC respectively.  Now you can think of the IC as a comparator with one side of the comparator having a precise 2.5V and the other side can be set using the reference pin.

This property comes in very handy for switching power supplies where the TL431 can used to compare the output voltage with desired voltage and provide a feedback to control switching frequency. Normally an Optocoupler is used along with this set-up to isolate the high voltage side. Apart from this the IC finds applications in many circuits where a Zener diode can be used few of them are listed below.

Applications

• Switch mode Power supplies
• Isolated Power supply circuits
• Voltage comparators
• Current Regulation circuits

2D model (TO-92)

The IC is also available in 8-pin package. The dimensions of TO-92 package is shown below