The Amazing TL431 A Precise Programmable Reference So switch mode power supplies are amazing, right? I mean you simply plug them into mains voltage and then magically get granted access to a lower DC voltage on the output which you can use to charge your phone, your laptop or power pretty much anything in your modern households. And they do this voltage conversion with a pretty good efficiency. This article will delve into the world of switch mode power supplies and explore how they work, specifically focusing on the TL431 component and its role in feedback systems. Before diving into the details, it's essential to understand that this article is a simplified explanation of complex topics. For those interested in learning more about switch mode power supplies and feedback systems, there are many resources available online. So let's get started! The TL431 component is a precision voltage regulator that can be used to monitor voltages and switch at certain thresholds. This makes it perfect for monitoring circuits and providing feedback in power supplies. One of the most common applications of the TL431 is in adjustable Zener diodes. By adding a voltage divider between the cathode, ref pin, and anode, you can create an adjustable Zener diode with a stable output voltage. For example, using two 10kΩ resistors, you can create a 5V Zener diode. This technique allows you to make your own super-stable adjustable Zener diode, which is quite useful since not every Zener voltage exists with ordinary diodes. The TL431 can also be used in feedback circuits, such as the one shown below. This circuit will cut the current to a load when a certain adjustable under-voltage value is reached. Another example of a handy circuit that utilizes the TL431 is a precision constant current sink. By using a potentiometer, you can fine-tune the current output. Now, let's take a closer look at switch mode power supplies and how they use the TL431 in their feedback systems. Before we dive into the circuit, it's essential to understand that this explanation will be simplified and won't cover advanced topics like Laplace transformations. Let's imagine a basic flyback converter schematic whose output voltage we want to keep at 5V. In a normal feedback loop system, you would need to decrease the voltage with a voltage divider and then compare it to a stable reference voltage. The error amplifier amplifies the error voltage between the two inputs and sends it over to our PWM circuit through an optocoupler. The system works with negative feedback, so if the output voltage increases, the analog error voltage at the PWM circuit decreases, and thus the output PWM duty cycle decreases as well. However, in many power supplies, you won't see pure error amplifiers because the TL431 can do this job without a problem by adding a couple of passive components around it. Let's try to figure out their values. The voltage divider needs two 500Ω resistors since we once again need to reach 2.5V at the ref pin, and the output voltage should be 5V. The other resistor needs to pass 1mA for the TL431 and 1mA for the optocoupler LED. Since we know that the voltage drop across the LED is 1.2V, and across the TL431 is 2.5V, we can calculate a resistance of around 650Ω. Finally, there's the capacitor whose purpose and selection goes back to a whole lot of feedback control oscillation theory, but a 100nF one is a good start for tinkering. According to this final schematic, I built up my test power supply partly on a perf board and partly in the air, which was not really pretty to look at. I also had to do some teensy programming to create the required sawtooth signal with a frequency of 54kHz. And as you can see after doing a couple of tests, the feedback system seems to be acceptably stable and works pretty much as expected. So feel free to build such a low voltage switch mode converter by yourself and be amazed what this small TL431 component can all do. If you're interested in learning more about switch mode power supplies and feedback systems, there are many resources available online. This article has provided a simplified explanation of the TL431 component and its role in these systems. Happy building! Power Supplies A power supply is an electrical device that supplies electric power to a load or group of loads, such as a computer, electronic device, or machine. The primary function of a power supply is to convert the alternating current (AC) from the mains electricity supply into direct current (DC) that can be used by the load. Background The concept of power supplies dates back to the late 19th century, when the first electrical power distribution systems were developed. Initially, power supplies were simple devices that converted AC to DC using mechanical switches and electromagnets. With the advent of vacuum tubes and transistors in the mid-20th century, power supply design evolved to include more sophisticated components and circuitry. Types of Power Supplies There are several types of power supplies, including:   Linear Power Supplies Use a linear regulator to convert AC to DC.   Switch-Mode Power Supplies (SMPS) Use high-frequency switching to convert AC to DC, providing higher efficiency and smaller size.   Uninterruptible Power Supplies (UPS) Provide backup power during outages or failures, typically using batteries and inverters. The Amazing TL431: A Precise Programmable Reference The TL431 is a highly versatile and precise programmable reference voltage source that has been widely used in various electronic circuits. Its unique characteristics, high accuracy, and flexibility make it an ideal choice for many applications. Key Features of the TL431 Programmable reference voltage from 2.5V to 36V Tight tolerance: ±0.5% at room temperature, ±1% over the full operating range Low drift: 10μV/°C typical High output current capability: up to 100mA Wide operating temperature range: -40°C to +125°C How the TL431 Works The TL431 is a type of shunt regulator, which means it regulates the output voltage by sinking excess current to ground. The device consists of a precision reference amplifier, a feedback resistor network, and an NPN power transistor. Applications of the TL431 Voltage regulators for high-performance power supplies Reference voltage sources for analog-to-digital converters (ADCs) Power management circuits in battery-powered devices High-precision measurement instruments, such as multimeters and oscilloscopes Advantages of the TL431 High accuracy and stability over a wide temperature range Low noise and low drift characteristics Wide output voltage range and high output current capability Small size and low power consumption Conclusion The TL431 is an exceptional programmable reference voltage source that offers high accuracy, stability, and flexibility. Its unique characteristics make it an ideal choice for a wide range of applications, from power management circuits to high-precision measurement instruments. Q1: What is the TL431? The TL431 is a high-precision, programmable shunt voltage reference designed for use in a wide range of applications, including power supplies, instrumentation, and data acquisition systems. Q2: What makes the TL431 "amazing"? The TL431 is considered amazing due to its high accuracy (±0.5%), low drift over temperature (±10 ppm/°C), and ability to be programmed to provide a specific reference voltage. Q3: How does the TL431 work? The TL431 works by using an internal bandgap reference and a precision amplifier to regulate the output voltage. The output voltage is proportional to the input current, allowing it to be programmed using external resistors. Q4: What are some common applications of the TL431? The TL431 is commonly used in power supplies, instrumentation, data acquisition systems, and other applications where a precise reference voltage is required. Q5: Can the TL431 be used as a precision voltage regulator? Q6: How do I program the output voltage of the TL431? The output voltage of the TL431 can be programmed using external resistors. The ratio of the resistors sets the desired output voltage. Q7: What is the temperature range of the TL431? The TL431 operates over a temperature range of -40°C to +125°C, making it suitable for use in a wide range of applications. Q8: Is the TL431 available in different packages? Q9: Can I use the TL431 as a replacement for other voltage references? The TL431 can be used as a replacement for other voltage references in many applications, but it is recommended to consult the datasheet and application notes to ensure compatibility. Q10: Where can I find more information about the TL431? More information about the TL431 can be found in the datasheet, application notes, and technical documentation available from the manufacturer's website. No. Pioneers/Companies Contribution 1 Linear Technology (Now part of Analog Devices) Introduced the first programmable shunt regulator, the LT431 in 1986 2 Fairchild Semiconductor Developed the μA431, one of the first widely used programmable references in 1974 3 Bob Pease (Engineer at National Semiconductor) Designed the LM431, a highly popular and influential programmable reference in 1981 4 National Semiconductor Produced the LM431 and its variants, which became industry standards 5 Analog Devices Acquired Linear Technology and continues to produce advanced versions of the TL431 6 Texas Instruments Produces a range of programmable references, including the TLV431 and TLVH431 7 ON Semiconductor Offers a variety of programmable references, including the NCP431 and NCP432 8 STMicroelectronics Produces advanced programmable references, such as the TL431 and its variants 9 Diodes Incorporated Offers a range of programmable references, including the AP431 and AZ431 10 Micrel (Now part of Microchip Technology) Produced innovative programmable references, such as the MIC431 and its variants Parameter Value Unit Description Reference Voltage 2.495V (typ) V The nominal reference voltage of the TL431. Maximum Reference Voltage Drift ±10mV mV The maximum allowed drift in reference voltage over temperature and time. Input Offset Voltage 2.0mV (typ) mV The difference between the actual input voltage and the ideal input voltage. Input Bias Current 100nA (typ) nA The current drawn by the TL431's input stage. Output Voltage Range 2.495V to 36V V The range of output voltages that can be programmed using the TL431. Output Current Range 1mA to 100mA mA The range of output currents that can be sourced or sunk by the TL431. Cathode Voltage Range -0.3V to 36V V The range of voltages that can be applied to the cathode pin of the TL431. Anode-to-Cathode Voltage Drop 2.0V (typ) V The voltage drop between the anode and cathode pins when the device is conducting. Operating Temperature Range -40°C to +125°C °C The range of temperatures over which the TL431 can operate. Storage Temperature Range -65°C to +150°C °C The range of temperatures over which the TL431 can be stored without damage. Pin Description Function Anode (A) The anode pin is connected to the positive side of the reference voltage. Cathode (K) The cathode pin is connected to the negative side of the reference voltage and is also used as a current sink or source. Reference (R) The reference pin is used to set the output voltage of the TL431 using an external resistor divider network. Package Options Description DIP-8 A through-hole package with eight leads. SOIC-8 A surface-mount package with eight leads. TSSOP-8 A thin shrink small outline package with eight leads. Ordering Information Description TL431ACD A fixed-voltage version of the TL431 with a reference voltage of 2.495V. TL431BID A variable-voltage version of the TL431 that can be programmed using an external resistor divider network. TL431CD A high-precision version of the TL431 with a maximum reference voltage drift of ±5mV. Applications Description Voltage Regulation The TL431 can be used as a voltage regulator to provide a stable output voltage from a variable input voltage. Current Limiting The TL431 can be used as a current limiter to limit the maximum current drawn by a load. Power Supplies The TL431 is commonly used in power supplies, such as switching regulators and linear regulators. Key Features Description Precision Reference Voltage The TL431 provides a precision reference voltage with a maximum drift of ±10mV. Programmable Output Voltage The TL431's output voltage can be programmed using an external resistor divider network. High Output Current Capability The TL431 is capable of sourcing or sinking up to 100mA of current. Cautions and Warnings Description Handling Precautions The TL431 is sensitive to electrostatic discharge (ESD) and should be handled using anti-static precautions. Thermal Considerations The TL431's junction temperature should not exceed 150°C to prevent damage to the device. Reverse Polarity Protection The TL431 does not have built-in reverse polarity protection and may be damaged if subjected to reverse polarity voltages. Terminology Description Anode (A) The positive side of the reference voltage. Cathode (K) The negative side of the reference voltage and current sink/source pin. Reference Voltage The output voltage of the TL431, typically 2.495V. Revision History Description Rev A (Initial Release) The initial release of the TL431 datasheet. Rev B (Updated Electrical Characteristics) An update to the electrical characteristics section of the datasheet. Trademarks and Copyrights Description Texas Instruments A registered trademark of Texas Instruments Incorporated. TL431 A trademark of Texas Instruments Incorporated.