## Overview of the LM337L The **LM337L** is an adjustable 3-terminal negative voltage regulator. It is the low-power version of the standard LM337, designed to provide a regulated negative output voltage that can be adjusted from **-1.2V to -37V**. It is frequently paired with the **LM317L** (the positive counterpart) in split-rail power supply designs. --- ### 1. Key Technical Specifications | Feature | Specification | | :--- | :--- | | **Output Voltage Range** | -1.2V to -37V | | **Output Current** | Up to 100mA | | **Input-Output Differential** | Max 40V | | **Line Regulation** | 0.01% / V (Typical) | | **Load Regulation** | 0.1% (Typical) | | **Package Types** | TO-92, SOIC-8, SOT-89 | | **Operating Temperature** | 0°C to +125°C | --- ### 2. Pin Configuration (TO-92 Package) Unlike positive regulators where the center pin is often Ground, the LM337L has a specific layout that must be followed carefully to avoid damage: 1. **ADJ (Adjust):** Used to set the output voltage via a resistive divider. 2. **Output:** The regulated negative voltage. 3. **Input:** The unregulated negative supply voltage. --- ### 3. Basic Circuit and Voltage Calculation To set the output voltage, two resistors ($R_1$ and $R_2$) are required. The $R_1$ resistor is usually placed between the **Output** and **ADJ** pins. **Formula:** $$V_{out} = -1.25V \times (1 + \frac{R_2}{R_1})$$ #### Essential External Components: * **$C_{in}$ (0.1µF):** Required if the regulator is far from the power supply filter capacitor (Tantalum preferred). * **$C_{out}$ (1µF):** Improves transient response and stability. * **$R_1$:** Typically 120$\Omega$ to 240$\Omega$ to ensure the minimum load current requirement is met. --- ### 4. Comparison: LM337 vs. LM337L | Feature | LM337 (Standard) | LM337L (Low Power) | | :--- | :--- | :--- | | **Max Current** | 1.5A | 100mA | | **Package** | TO-220 / TO-3 | TO-92 / SO-8 | | **Best Use Case** | High power supplies | Signal processing / Op-amp biasing | --- ### 5. Protection Features The LM337L includes several internal safety mechanisms: * **Thermal Overload Protection:** Shuts down the device if the internal temperature exceeds limits. * **Short Circuit Current Limiting:** Limits the maximum output current to prevent burnout. * **Safe Area Protection:** Protects the internal output transistor during high voltage-to-current stress.