## Technical Overview: TL431L-AF5-R The **TL431L-AF5-R** is a precision shunt regulator diode, often referred to as an "adjustable Zener diode." It is widely used in power supply circuits for voltage regulation and monitoring due to its high stability and low temperature coefficient. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Output Voltage ($V_{ref}$)** | 2.495V (Adjustable up to 36V) | | **Voltage Tolerance** | ±0.5% (High Precision) | | **Package Type** | SOT-25 / SOT-23-5 | | **Operating Current Range** | 1.0mA to 100mA | | **Dynamic Impedance** | 0.22 $\Omega$ (Typical) | | **Operating Temperature** | -40°C to +125°C | --- ### 2. Pin Configuration (SOT-25/AF5) The "AF5" suffix typically denotes the SOT-25 (SOT-23-5) package. Note that pinouts can vary slightly by manufacturer, but the standard UTC (Unisonic Technologies) layout is as follows: 1. **Cathode (K):** The positive terminal of the regulator. 2. **Anode (A):** The negative terminal (usually connected to ground). 3. **Reference (Ref):** The input pin used to set the output voltage via a divider. 4. **NC/VCC:** Often No Connection or internal bias depending on specific sub-variants. 5. **NC:** No Connection. --- ### 3. Functional Description The device functions as an error amplifier with a built-in 2.495V reference. When the voltage at the **REF** pin exceeds the internal threshold, the device begins to conduct current from the **Cathode** to the **Anode**. #### Voltage Calculation Formula To set an output voltage higher than 2.495V, two external resistors ($R_1$ and $R_2$) are used: ```math V_{out} = V_{ref} \times (1 + \frac{R_1}{R_2}) ``` --- ### 4. Common Applications * **Switch Mode Power Supplies (SMPS):** Used in the feedback loop (often paired with an optocoupler) to provide isolated voltage regulation. * **Voltage Monitoring:** Acts as a comparator for over-voltage or under-voltage detection. * **Precision Current Limiter:** Used with a pass transistor to create a constant current source. * **Zener Diode Replacement:** Offers a much sharper "knee" and better temperature stability than standard Zener diodes. --- ### 5. Part Number Breakdown * **TL431:** Base model number (Programmable Shunt Regulator). * **L:** Low voltage/Low current optimized or specific tolerance grade (Manufacturer dependent). * **AF5:** Package code for SOT-25. * **R:** Tape & Reel packaging.