🔹 2PCS L7912CV – Fixed -12V Negative Voltage Regulator (TO-220)
A monolithic integrated circuit designed as a fixed-output, negative voltage regulator. The L7912CV provides a stable -12V DC output from a higher unregulated negative input voltage (down to -14.5V). It is the negative rail complement to the popular L7812 positive regulator, essential for creating symmetrical ±12V power supplies in audio, op-amp, and analog circuits.
✅ Specifications:
Part Number: L7912CV (Common TO-220 commercial grade variant)
Type: Linear Negative Voltage Regulator
Output Voltage: Fixed -12V DC (±2% typical)
Output Current: Up to 1.5A (with adequate heatsinking)
Input Voltage Range: -14.5V to -35V DC (Recommended)
Dropout Voltage: ~1.1V (Minimum required difference between |Vin| and |Vout|)
Line Regulation: 60 mV (Typ.)
Load Regulation: 120 mV (Typ.)
Ripple Rejection: 55 dB (Typ.)
Package: TO-220 (Through-Hole, with metal tab for heatsinking)
Pinout (TO-220, front view, tab facing you):
Ground (GND)
Input (Vin) – Connect to the negative unregulated DC input.
Output (Vout) – Provides regulated -12V.
The metal tab is connected to Pin 2 (Input).
Protections: Internal overcurrent, thermal shutdown, and safe-area compensation.
Operating Temperature: 0°C to +125°C
Quantity: 2 pieces
⚙️ Key Features:
Fixed Negative Output: No external components needed to set the voltage (only input/output capacitors).
Robust Protection: Built-in safeguards protect the regulator and your circuit.
Easy to Use: Classic 3-terminal design, symmetrical to the L7812.
Wide Input Range: Can regulate from common negative supplies like -15V, -18V, or -24V down to a clean -12V.
Industry Standard: A ubiquitous component for dual-rail power systems.
📦 Typical Applications:
Dual/Split Power Supplies: Creating the negative rail (±12V) for op-amps, audio equipment, and analog circuits when paired with an L7812.
Negative Voltage Rails: Powering negative-only circuitry in test equipment, communication devices, or industrial controls.
Voltage Regulation from Negative Sources: Stabilizing the output of a negative DC supply or rectifier.
DIY Audio Amplifiers: Providing the negative supply for amplifier stages.
Bench Power Supplies: As a building block for adjustable or fixed negative output modules.
🔧 Basic Connection (for a ±12V Supply):
Input Capacitor (Cin): Place a 0.33µF ceramic capacitor and a 1-10µF electrolytic capacitor (positive lead to ground, negative lead to Vin) close to the IC’s input pin (Pin 2). Note polarity for negative supply.
Output Capacitor (Cout): Place a 0.1µF ceramic capacitor and a 10-100µF electrolytic capacitor (positive lead to ground, negative lead to Vout) close to the output pin (Pin 3).
Ground: Connect Pin 1 to the system ground (0V reference).
Heatsinking: Required if power dissipation exceeds ~1-2W. Power Dissipation: Pd=(∣Vin∣−∣Vout∣)×Iload. For example, with -18V input, -12V output, and 1A load: (18−12)×1=6W → a substantial heatsink is mandatory. The TO-220 tab is live (connected to Vin), so use an insulating thermal pad if the heatsink is shared or grounded.
⚠️ Critical Design Notes & Warnings:
Negative Voltage Polarity: Pay extreme attention to polarity. The input and output are negative relative to ground. Electrolytic capacitors must be connected with their POSITIVE (+) leads to ground and negative leads to the regulator pins.
Minimum Input Voltage: Requires input to be at least -14.5V to maintain -12V regulation. For a -12V output, plan for ≥ -14.5V input.
Heatsink & Isolation: The tab is at INPUT voltage (Pin 2), which is negative. If attaching to a common or grounded heatsink, you must use an electrically insulating mica/silicon pad and shoulder washer.
Linear Regulator Inefficiency: Dissipates excess voltage as heat. For high input-output differentials or high currents, consider a switching regulator for the negative rail.
Reverse Polarity Protection: This IC does not protect against reversed input polarity. Add a series diode on the input if needed.
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