Overview

The LM7815 (and TO-220 packaged L7815CV / LM7815CT) is a 3-terminal fixed positive linear voltage regulator IC manufactured by STMicroelectronics, Texas Instruments, and ON Semiconductor. It delivers a stable, low-noise $+15.0\text{V}$ DC power supply rail from unregulated DC input voltages ranging from $17.5\text{V}$ to $35.0\text{V}$.

Commonly paired with its negative counterpart, the LM7915 ($-15\text{V}$), the LM7815 forms the classic $\pm 15\text{V}$ split power supply rail essential for high-fidelity audio preamplifiers, analog synthesizer modules, instrumentation op-amps, and active filters. It features internal thermal overload protection, short-circuit current limiting, and output transistor safe operating area (SOA) protection.

Quick reference

Pinout (TO-220 Package)

Looking at the front labeled face of the TO-220 package with metal tab at top and leads pointing down:

        ┌──────────────┐
        │ [LM7815 Tab] │  (Metal Tab connected internally to Pin 2 GND)
        ├──────────────┤
        │    LM7815    │  (Front Face)
        └─┬────┬────┬──┘
          1    2    3
         IN   GND  OUT

Specifications

Standard Circuit & Capacitors

       +V_IN Unregulated Input (17.5V - 35V DC)
          │
       [Pin 1: IN]
        LM7815
       [Pin 3: OUT] ──────────────┬─────────────── +15.0V Regulated DC Output
          │                       │
       [Pin 2: GND]          [ C2 = 0.1µF Ceramic ]
          │                       │
   [ C1 = 0.33µF Ceramic ]       GND
          │
         GND

• Input Capacitor ($C_1 = 0.33\ \mu\text{F}$): Essential when the regulator is located more than a few inches from the bridge rectifier / bulk filter capacitor to prevent inductive oscillations.
• Output Capacitor ($C_2 = 0.1\ \mu\text{F}$): Ceramic or tantalum capacitor to improve transient response and ensure high-frequency stability.

Common mistakes

• Insufficient input headroom: Supplying less than $17.5\text{V}$ input causes the regulator to drop out of regulation. Under heavy load ($1\text{A}$), input ripple valleys must not drop below $17.5\text{V}$.
• Excessive thermal dissipation: In a 24V-to-15V step-down at 1A, the power dissipated is $(24\text{V} - 15\text{V}) \times 1\text{A} = 9\text{ Watts}$. A TO-220 package without a heatsink will thermal throttle within seconds.
• Confusing LM7815 and LM7915 pinouts: The negative voltage complementary part (LM7915) has a completely different pinout (Pin 1: GND, Pin 2: IN, Pin 3: OUT, Tab: IN). Never assume 78xx and 79xx share the same pin assignments.

Notes

• Split Supply Pair: Often deployed alongside the LM7915 ($-15\text{V}$) to provide balanced $\pm 15\text{V}$ rails for operational amplifiers (such as TL072, NE5532, and OPA2134).