### Overview of the TL431LG-AE3-R The **TL431LG-AE3-R** is a precision programmable shunt voltage reference. It is widely used in power supply circuits to provide a stable reference voltage or to act as an error amplifier in feedback loops. --- ### Part Number Breakdown Understanding the specific suffix of this part helps identify its package and manufacturer (UTC - Unisonic Technologies): | Component Segment | Meaning | | :--- | :--- | | **TL431** | Base Part Number (Adjustable Precision Shunt Regulator) | | **L** | Lead-Free / Halogen-Free (Green product) | | **G** | Grade / Specific Accuracy (usually ±0.5% or ±1% depending on datasheet) | | **AE3** | Package Type: **SOT-23** | | **R** | Tape and Reel (Packaging method) | --- ### Technical Specifications The device acts like a Zener diode, but with a programmable breakdown voltage determined by two external resistors. | Parameter | Value (Typical) | | :--- | :--- | | **Reference Voltage ($V_{ref}$)** | 2.495 V | | **Output Voltage Range** | $V_{ref}$ to 36 V | | **Cathode Current ($I_k$)** | 1.0 mA to 100 mA | | **Dynamic Impedance** | 0.2 $\Omega$ (Typical) | | **Temperature Stability** | 50 ppm/°C | | **Operating Temperature** | -40°C to +85°C | --- ### Pin Configuration (SOT-23) The SOT-23 package is a 3-pin surface mount device. | Pin Number | Name | Function | | :--- | :--- | :--- | | 1 | **Reference (REF)** | The input to the internal comparator; used to set output voltage. | | 2 | **Cathode (K)** | The "output" or positive terminal (similar to Zener cathode). | | 3 | **Anode (A)** | The ground or negative terminal. | --- ### Internal Functional Block Diagram The TL431 contains: 1. An **Internal Reference** (2.495V). 2. An **Error Amplifier**. 3. An **Output Transistor** (Open-collector/shunt). --- ### Common Applications * **Linear Regulators:** To provide a stable control voltage. * **Switching Power Supplies (SMPS):** Used on the secondary side of an optocoupler to provide feedback to the PWM controller. * **Voltage Monitoring:** To trigger an alarm or shut down a system when a specific voltage threshold is reached. * **Current Limiting:** Can be configured to sense current across a shunt resistor. --- ### Basic Design Formula To set the output voltage ($V_{out}$), you use two resistors ($R_1$ and $R_2$) in a voltage divider configuration: ```text Vout = Vref * (1 + R1 / R2) + Iref * R1 ``` *(Note: Since Iref is very small (~2µA), it is often ignored for standard calculations.)*