## Overview of LM317AL-TQ3-R The **LM317AL-TQ3-R** is a high-performance, adjustable 3-terminal positive voltage regulator. It is designed to supply more than 1.5A of load current with an output voltage adjustable over a range of 1.2V to 37V. The "AL" suffix typically denotes a higher precision version (tighter reference voltage tolerance), while "TQ3" refers to the package type (TO-263), and "R" indicates Tape & Reel packaging. --- ### 1. Key Technical Specifications | Parameter | Value / Range | | :--- | :--- | | **Output Voltage Range** | 1.25V to 37V | | **Output Current** | > 1.5A | | **Input-Output Differential** | 40V (Maximum) | | **Reference Voltage Tolerance** | ±1% (for 'A' version) | | **Line Regulation** | 0.01% / V (Typical) | | **Load Regulation** | 0.1% (Typical) | | **Operating Temperature** | -40°C to +125°C | --- ### 2. Pin Configuration (TO-263 Package) In the TQ3 (TO-263/D2PAK) surface-mount 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. Functional Features * **Internal Protection:** Includes internal short-circuit current limiting and thermal overload protection. These features make the device virtually "blow-out" proof. * **Floating Operation:** The regulator "floats" on the output voltage. Only the differential between input and output is relevant to the device's internal circuitry, allowing it to regulate high voltages as long as the $V_{in} - V_{out}$ limit is not exceeded. * **Elimination of Stocking:** Since it is adjustable, one part can replace many fixed-voltage regulators, reducing inventory costs. --- ### 4. Basic Application Circuit To set the output voltage, two external resistors are required. The formula for the output voltage is: $$V_{out} = 1.25V \times \left(1 + \frac{R_2}{R_1}\right) + I_{adj} \times R_2$$ ```c Vin ---- [ LM317AL ] ---- Vout | +-------+---- R1 ----+ | | | ADJ +------------+ | R2 | GND ``` --- ### 5. Package Information: TO-263 (TQ3) The **TQ3** package is a surface-mount version of the classic TO-220. It provides: * **Better Thermal Dissipation:** The large back tab is soldered directly to the PCB copper, acting as a heatsink. * **Space Efficiency:** Lower profile than through-hole components. * **Automated Assembly:** Suitable for high-speed pick-and-place machines.