The TL431 is a widely used adjustable shunt regulator, commonly manufactured by semiconductor companies like Texas Instruments, ON Semiconductor, STMicroelectronics, and others.
Let’s dive into the detailed explanation of the TL431's pin function, specifications, and circuit principle.
1. TL431 Pin Function and Specifications:
The TL431 has a 3-pin configuration and is usually housed in TO-92, TO-220, or SOT-23 packages. Below are the pin details:
Pin Number Pin Name Pin Function Description 1 Anode (A) The Anode pin is connected to the cathode of the Zener diode in the circuit and is typically connected to ground in voltage regulation configurations. 2 Cathode (K) The Cathode pin connects to the output of the circuit and is the output of the shunt regulator. This pin must be at a higher voltage than the Anode pin. 3 Reference (Ref) The Reference pin receives the external voltage reference and is used to set the shunt regulator’s reference voltage. It typically connects to a resistor network. Pin Configuration Overview:Pin 1 (Anode, A): It is connected to the cathode of the Zener diode (the low-voltage part of the voltage reference system). This pin is usually connected to ground in the circuit.
Pin 2 (Cathode, K): This is the output pin and must be at a higher potential than the Anode to function as a shunt regulator.
Pin 3 (Reference, Ref): This pin is responsible for setting the reference voltage. When the voltage at this pin exceeds the reference threshold, the TL431 will regulate the output voltage at the Cathode pin to a stable value.
2. TL431 Package Types:
The TL431 comes in several packages, the most common being:
TO-92 (Plastic Package) TO-220 (Through-hole) SOT-23 (Surface-mount)3. TL431 Detailed Pin Function in Different Packages:
Let’s take a detailed look at the functions of each pin:
Pin Number Pin Name Pin Function Description 1 Anode (A) Connect to the low side of the load or ground. In some configurations, this pin may have an external resistor to set voltage reference. 2 Cathode (K) This is the output, typically connected to a load or feedback loop for regulation. In voltage regulation applications, this is where the regulated voltage is output. 3 Reference (Ref) Used to apply an external reference voltage. The TL431 turns on (shunts current) when the voltage at this pin exceeds the internal reference threshold (~2.495V).4. Circuit Principle of TL431:
The TL431 is often used in voltage regulation circuits. When the voltage at the reference pin exceeds the internal reference value (typically 2.495V), the device turns on, creating a low-resistance path from the Cathode to the Anode. This allows the regulator to adjust the output voltage accordingly to maintain a constant value.
The TL431 is often used in precision voltage references, switch-mode power supplies (SMPS), and feedback loops for voltage regulation. It can regulate voltages in a variety of configurations, including buck, boost, and linear regulators.5. Frequently Asked Questions (FAQ) for TL431:
Q1: What is the reference voltage of the TL431? A1: The reference voltage of the TL431 is typically 2.495V.
Q2: How do I use the TL431 in a voltage regulator circuit? A2: You connect the reference pin to a resistor divider network and use the Cathode pin to regulate the output voltage.
Q3: What is the maximum output current of the TL431? A3: The maximum output current of the TL431 is typically 100mA.
Q4: How does the TL431 maintain voltage regulation? A4: When the voltage at the Reference pin exceeds the 2.495V threshold, the TL431 turns on and adjusts the Cathode voltage accordingly.
Q5: Can the TL431 be used in a feedback loop of a switching power supply? A5: Yes, it is commonly used in feedback loops of switching power supplies to maintain a regulated output voltage.
Q6: What is the temperature coefficient of the TL431? A6: The temperature coefficient is typically 30 ppm/°C, indicating very little change in the reference voltage with temperature.
Q7: What is the typical dropout voltage of the TL431? A7: The typical dropout voltage is 1.2V at 10mA output current.
Q8: Can I use the TL431 with higher voltages? A8: Yes, the TL431 can handle voltages up to 36V, but the voltage difference between the Anode and Cathode must always be within the specified limits.
Q9: What package options are available for the TL431? A9: The TL431 is available in TO-92, TO-220, and SOT-23 packages.
Q10: How do I select the appropriate resistor values for the feedback loop? A10: The resistor values can be selected based on the desired output voltage and the reference voltage of 2.495V.
Q11: Can I use the TL431 as a precision voltage reference? A11: Yes, the TL431 can be used as a precision voltage reference in applications requiring accurate voltage regulation.
Q12: What is the quiescent current of the TL431? A12: The typical quiescent current is about 1mA, making it efficient for low-power applications.
Q13: Is the TL431 suitable for high-speed switching applications? A13: The TL431 is not intended for high-speed switching but works well in low-frequency regulation applications.
Q14: Can the TL431 be used for over-voltage protection circuits? A14: Yes, the TL431 can be used for over-voltage protection by setting a threshold voltage for when the shunt regulator turns on.
Q15: What is the typical response time of the TL431 in regulation circuits? A15: The response time is typically in the range of microseconds, depending on the external components.
Q16: What is the output voltage range of the TL431? A16: The output voltage is typically regulated around 2.495V but can be adjusted with an external resistor network.
Q17: Can I use the TL431 in a non-inverting configuration? A17: Yes, the TL431 can be used in both inverting and non-inverting configurations, depending on how it is wired in the circuit.
Q18: What are the failure modes of the TL431? A18: Common failure modes include overheating, excessive voltage, or current beyond the specified limits, leading to malfunction.
Q19: How do I connect the TL431 in a buck converter circuit? A19: In a buck converter, the TL431 is typically used to regulate the output voltage by providing feedback to the PWM controller.
Q20: Can the TL431 be used for current regulation circuits? A20: While primarily used for voltage regulation, the TL431 can also be adapted for use in current regulation circuits by modifying the feedback network.
6. TL431 Pin Function and Application Summary:
The TL431 is a versatile and highly accurate shunt voltage regulator that is widely used in various electronics, especially for precision regulation. It provides reliable voltage regulation in systems like power supplies and feedback circuits.
