## Overview of the LM317AL-TN3-R The **LM317AL-TN3-R** is a high-performance, adjustable 3-terminal positive voltage regulator. It is designed to supply more than 100mA of load current with an output voltage adjustable over a range of 1.2V to 37V. The suffix **"TN3"** typically refers to the **TO-252 (DPAK)** package, while the **"R"** denotes the tape and reel packaging for automated assembly. --- ### 1. Key Technical Specifications | Parameter | Specification | | :--- | :--- | | **Output Voltage Range** | 1.25V to 37V | | **Output Current** | 100mA (Minimum) | | **Input-Output Differential** | 40V (Maximum) | | **Line Regulation** | 0.01% / V (Typical) | | **Load Regulation** | 0.1% (Typical) | | **Operating Temperature** | -40°C to +125°C | | **Package Type** | TO-252 (Surface Mount) | --- ### 2. Pin Configuration (TO-252) In the DPAK (TN3) package, the pinout is generally as follows: 1. **ADJ (Adjust):** Used to set the output voltage via a resistor divider. 2. **Vout (Output):** The regulated output voltage (also connected to the large metal tab). 3. **Vin (Input):** The unregulated input voltage. --- ### 3. Basic Application Circuit To set the output voltage, the LM317AL requires two external resistors ($R_1$ and $R_2$). The internal reference voltage ($V_{ref}$) is 1.25V. #### Voltage Formula: $V_{out} = V_{ref} \times (1 + \frac{R_2}{R_1}) + (I_{adj} \times R_2)$ #### Typical Circuit Code Representation: ```text Vin ---- [LM317AL] ---- Vout | | | [R1] | | +-----+----- Vout | [R2] | GND ``` --- ### 4. Distinctive Features * **Internal Protection:** Includes internal short-circuit current limiting and thermal overload protection. These features make it virtually "blow-out proof." * **Floating Operation:** The regulator "floats" on the output voltage. As long as the maximum input-to-output voltage differential is not exceeded, it can regulate supplies at very high voltages. * **Elimination of Stockpiling:** Because the output is adjustable, one part can replace many fixed-voltage regulators in your inventory. --- ### 5. Common Use Cases 1. **Local On-card Regulation:** Reducing noise by regulating power close to the load. 2. **Programmable Output Regulation:** Used in lab power supplies. 3. **Constant Current Regulator:** By placing a fixed resistor between the Output and Adjust pins.