2pcs L7912CV Voltage regulator

🔹 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):

  1. Ground (GND)

  2. Input (Vin) – Connect to the negative unregulated DC input.

  3. 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):

1. 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.

2. 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).

3. Ground: Connect Pin 1 to the system ground (0V reference).

4. Heatsinking: Required if power dissipation exceeds ~1-2W. Power Dissipation: Pd=(∣Vin∣−∣Vout∣)×IloadPd​=(∣Vin​∣−∣Vout​∣)×Iload​. For example, with -18V input, -12V output, and 1A load: $(18-12)\times 1=6W$ → 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.