TL431 Adjustable Voltage Regulator Pinout, Specs & Applications
The TL431 series ICs are three-terminal adjustable shunt regulators with guaranteed thermal stability over a full operation range. These ICs feature sharp turn-on characteristics, low temperature coefficient and low output impedance, which make them ideal substitutes for Zener diodes in applications such as switching power supply, charger and other adjustable regulators.
The TL431 voltage type is 40V. The output voltage can be set to any value between VREF(2.5V) and the corresponding maximum cathode voltage.
The TL431 precision reference is offered in two band gap tolerance: 0.4% and 1.0%.
PIN Configuration
Pin Assignment
The TL431 provides stable performance over a wide operating temperature range. And it can also be used when the Zener diode needs to be replaced in various applications because its working principle is almost similar to the Zener diode except that the output voltage is programmable and adjustable. It is widely used in overvoltage and undervoltage monitoring circuits, window voltage monitoring circuits, power supplies as reference voltage sources, etc.
Topdiode Selection Guide
Features
- Programmable Precise Output Voltage from 2.5V to 36V
- Very Accurate Reference Voltage: Typical 0.15%
- High Stability under Capacitive Load
- Low Temperature Deviation: Typical 4.5mV
- Low Equivalent Full-range Temperature
- Coefficient with 20PPM/°C Typical
- Low Dynamic Output Resistance: Typical 0.2Ω
- Sink Current Capacity from 1mA to 100 mA
- Low Output Noise
- Wide Operating Range of -40 to 150°C
Regulator integrated circuit
The circuit diagram using the TL431 voltage regulator integrated circuit is shown below:
In the above circuit diagram, it can be observed that the NPN transistor is biased from the op-amp with a precise reference voltage rating of 2.5 volts on the non-inverting terminal. The collector terminal of the transistor is connected to the cathode terminal of the TL4311C, and the emitter terminal of the transistor is connected to the anode terminal of the TL431 IC.
Now consider the TL431 voltage regulator used as a comparator, one side of the comparator will have an exact voltage of 2.5 volts and the other side is set with the help of the reference terminal. This feature is mainly suitable for SMPS (Switch Mode Power Supply) because the TL431 regulator can compare the obtained output voltage with the desired output voltage and control the switching frequency by providing a feedback path. To isolate the high voltage section, optical couples are often used with this circuit setup.
Test Circuit
The adjustable range of the output voltage Vo is between 2.6 volts and 36 volts, and the expression of the output voltage Vo is written as:
Vo=Vref(1+R1/R2)
Because Vref is set to 2.5 volts, the voltage the circuit can withstand is related to (Vo-Vi). If there is a large voltage difference, the power dissipated by the resistor increases.
Main application
The following is a brief list of some applications of the TL431 voltage regulator:
For SMPS (switched mode power supply)
Used in isolated power circuits
For voltage comparators with integrated reference
Used in current regulation circuits
For use in precision voltage reference circuits
For over voltage protection circuits
For voltage monitor
For constant current source circuit
For controlled shunt characteristics
Can be used when the Zener diode needs to be replaced
Used in monitor and battery charger circuits
The TL431 is a widely used adjustable precision voltage reference and linear regulator, known for its low temperature drift, high accuracy, and versatile applications. It can function as a voltage reference or be incorporated into switching power supplies, over-voltage protection circuits, battery chargers, and current sensing applications. With its low cost, stability, and broad applicability, the TL431 has become an essential component in electronic circuit design.
