The **LL431G-AE3-R** is a specific part number for a programmable precision shunt regulator diode. It is widely used in power management circuits to provide a stable reference voltage. Below is a detailed breakdown of its electronic characteristics and specifications. ### 1. General Overview The LL431G is a three-terminal adjustable shunt regulator with guaranteed thermal stability over the applicable temperature range. It acts like a Zener diode but with a programmable output voltage. | Attribute | Specification | | :--- | :--- | | **Type** | Programmable Shunt Regulator | | **Package** | SOT-23 (indicated by the "AE3" code) | | **Reference Voltage ($V_{ref}$)** | 2.495V (Typical) | | **Output Voltage Range** | $V_{ref}$ to 36V | | **Accuracy** | Generally 0.5% or 1% (Suffix dependent) | --- ### 2. Pin Configuration (SOT-23) The device typically features three pins. In a standard SOT-23 package for this part: 1. **Reference (REF):** Input to the internal comparator; used to set the output voltage via a resistor divider. 2. **Cathode (K):** The positive terminal (equivalent to the cathode of a Zener). 3. **Anode (A):** The common/ground terminal. --- ### 3. Key Technical Specifications | Parameter | Value / Limit | | :--- | :--- | | **Cathode Voltage ($V_{KA}$)** | Max 37V | | **Continuous Cathode Current ($I_K$)** | -100mA to +150mA | | **Minimum Current for Regulation** | 1.0mA (Typical) | | **Dynamic Impedance** | 0.2 $\Omega$ (Typical) | | **Temperature Range** | -40°C to +125°C | --- ### 4. Circuit Functionality The device functions by comparing the voltage at the **REF** pin to its internal bandgap reference. * If $V_{REF}$ exceeds 2.495V, the device increases current flow through the **Cathode** to pull the voltage down. * The output voltage ($V_{OUT}$) is calculated using the following formula: `Vout = Vref * (1 + R1/R2)` ### 5. Part Number Decoding The suffix **LL431G-AE3-R** usually breaks down as follows: * **431:** The industry-standard series (TL431 compatible). * **G:** Green / Halogen Free. * **AE3:** Package code for **SOT-23**. * **R:** Tape and Reel packaging. --- ### 6. Common Applications * **Switching Power Supplies (SMPS):** Used in the feedback loop (with an optocoupler) to regulate output voltage. * **Voltage Monitoring:** Acting as a comparator with a precise threshold. * **Constant Current Source:** Maintaining a fixed current across a load. * **Zener Diode Replacement:** For higher precision and lower temperature drift.