## Technical Overview: TL431-AE3-R The **TL431-AE3-R** is a precision programmable shunt regulator diode. It is widely used in power management circuits as a voltage reference because its output voltage can be set to any value between $V_{ref}$ (2.5V) and 36V using two external resistors. ### 1. Key Specifications The following table summarizes the primary electrical characteristics of the TL431-AE3-R: | Parameter | Symbol | Typical Value | Unit | | :--- | :--- | :--- | :--- | | **Reference Voltage** | $V_{ref}$ | 2.495 (±0.5% or 1%) | V | | **Cathode Voltage Range** | $V_{KA}$ | $V_{ref}$ to 36 | V | | **Cathode Current Range** | $I_K$ | 1.0 to 100 | mA | | **Reference Input Current** | $I_{ref}$ | 2.0 to 4.0 | µA | | **Dynamic Impedance** | $Z_{KA}$ | 0.22 | $\Omega$ | | **Operating Temperature** | $T_{opr}$ | -40 to +85 | °C | | **Package Type** | - | SOT-23 | - | --- ### 2. Part Number Breakdown (UTC Coding) The suffix **AE3-R** provides specific details regarding the packaging and physical form: * **TL431**: Device Base Number (Programmable Precision Reference). * **AE3**: Package code for **SOT-23**. * **R**: Tape & Reel packaging. --- ### 3. Pin Configuration (SOT-23) In the SOT-23 package, the pins are typically assigned as follows: 1. **Reference (R)**: The input pin that monitors the output voltage. 2. **Cathode (K)**: The "output" pin connected to the positive side. 3. **Anode (A)**: The ground/negative pin. --- ### 4. Basic Application Circuit To set the output voltage ($V_{out}$), a voltage divider is connected to the Reference pin. The formula to calculate the output voltage is: $$V_{out} = V_{ref} \times \left(1 + \frac{R1}{R2}\right) + I_{ref} \times R1$$ *(Note: Since $I_{ref}$ is very small, it is often ignored for general calculations.)* ```text (Input Voltage) | [Resistor R_bias] | +---------- Output (Cathode) | | | [R1] | | [TL431] <-----+ (Reference Pin) | | | [R2] | | (GND) (GND) ``` ### 5. Common Use Cases * **Shunt Regulator:** Providing a stable voltage reference in power supplies. * **Isolated Feedback:** Used alongside an **Optocoupler** in Switch Mode Power Supplies (SMPS) to provide feedback from the secondary to the primary side. * **Voltage Monitoring:** Acting as a comparator to trigger an alarm or shut down a system when voltage thresholds are exceeded. * **Current Limiting:** Used in constant current source circuits.