The Original 78L33 (L78L33ACZ / MC78L33ACP) Positive Fixed Linear Voltage Regulator is an industry-standard three-terminal monolithic voltage regulator integrated circuit manufactured by STMicroelectronics / ON Semiconductor / Texas Instruments. Encapsulated in a classic TO-92 through-hole package, it is designed to provide a stable, low-noise regulated +3.3V DC power rail with output currents up to 100mA from unregulated DC inputs up to 30V. Built with internal thermal overload protection, internal short-circuit current limiting, and tight ±5% output voltage tolerance, the 78L33 serves as an essential point-of-load regulator. It is widely used in 3.3V microcontroller circuits, analog sensor nodes, DIY breadboard prototypes, audio preamplifiers, and battery-powered electronics.

Specifications

• Part Number / Model: 78L33 / L78L33ACZ / MC78L33ACP (Commercial Temperature Range)
• Device Function: 3-Terminal Fixed Positive Linear Voltage Regulator
• Package Type: TO-92 
• Nominal Output Voltage (Vout): +3.3V DC (Tolerance: ±5% / 3.135V to 3.465V over temperature)
• Maximum Output Current (Iout): 100 mA (Continuous)
• Input Voltage Range (Vin): 5.3V to 30V DC (Absolute Maximum: 30V DC)
• Dropout Voltage (Vd): Typ. 1.7V to 2.0V (at Iout = 40mA to 100mA, Ta = 25°C)
• Quiescent / Bias Current (Iq): Typ. 3.0 mA / Max. 5.5 mA (at Vin = 8.3V, Iout = 40mA)
• Line Regulation: Typ. 20 mV / Max. 150 mV (at Vin = 5.3V to 20V, Iout = 40mA)
• Load Regulation: Typ. 15 mV / Max. 60 mV (at Iout = 1mA to 100mA, Vin = 8.3V)
• Ripple Rejection Ratio (PSRR / SVR): Typ. 49 dB to 54 dB (at f = 120Hz, Vin = 6.3V to 16.3V)
• Output Noise Voltage (eN): Typ. 40 µV (f = 10Hz to 100kHz)
• Short-Circuit Current Limit (Isc): Typ. 140 mA (at Vin = 8.3V)
• Total Power Dissipation (Pd): Up to 625 mW (at Ta = 25°C in free air, internally limited)
• Operating Junction Temperature (Tj): 0°C to +125°C
• Storage Temperature Range (Tstg): -65°C to +150°C
• Thermal Resistance, Junction to Ambient (Rth(j-a)): ~160°C/W to 200°C/W
• Pinout Configuration (Standard TO-92 - Front Flat Face Facing You, Leads Pointing Down):
  • Pin 1 (Left): Output Voltage (VOUT - +3.3V)
  • Pin 2 (Center): Ground (GND)
  • Pin 3 (Right): Input Voltage (VIN)

Features

• Stable +3.3V Point-of-Load Regulation: Supplies clean, low-ripple +3.3V DC power directly at the circuit board level, preventing ground loops and voltage drop issues caused by long supply wires.
• Wide 5.3V to 30V Input Voltage Range: Easily steps down multi-cell batteries, 9V alkaline cells, 12V DC adapters, and 24V industrial rails to logic-level 3.3V.
• Internal Thermal Shutdown: Automatically clamps and shuts off output current if internal silicon junction temperature reaches dangerous levels (~150°C).
• Internal Short-Circuit Current Limiting: Protects the regulator and upstream power supply from permanent damage during accidental output shorts to ground.
• Breadboard & Prototyping Friendly: Classic 0.1-inch (2.54mm) lead spacing in a compact TO-92 package makes it easy to use on breadboards, perfboards, and through-hole PCBs.
• Low Output Noise: Generates an ultra-clean DC supply without high-frequency switching hash, ideal for sensitive analog-to-digital converters (ADCs), DACs, and RF receivers.

Common Applications

• 3.3V Microcontroller Rails: Powering 3.3V microcontrollers (e.g., STM32, ESP8266/ESP32 sensor modules, CH32V, PIC) from 5V, 9V, or 12V power sources.
• Analog & Digital Sensor Nodes: Clean point-of-load power supply for I2C/SPI environmental sensors, accelerometers, and optical modules.
• Precision Voltage References: Low-power +3.3V reference for operational amplifier comparator networks and measurement circuits.
• Battery-Operated Handheld Meters: Stepping down 9V batteries or multi-cell Li-ion packs in portable instruments.
• Audio Preamplifiers & DAC Filters: Ultra-quiet DC bias rails for low-noise operational amplifier stages.

Usage Tips

• Input & Output Bypass Capacitors: Connect a **0.33µF (or 1µF) ceramic/tantalum capacitor** directly between Pin 3 (VIN) and Pin 2 (GND) to suppress input inductive ringing, and a **0.1µF to 1µF capacitor** between Pin 1 (VOUT) and Pin 2 (GND) to guarantee loop stability and improve transient response.
• Check TO-92 Pinout Orientation: Standard 78Lxx pinout in TO-92 is **VOUT (Pin 1), GND (Pin 2), VIN (Pin 3)** from left to right with the flat printed face toward you. Note that this is different from standard 78xx TO-220 regulators (which are VIN, GND, VOUT).
• Ensure Adequate Voltage Headroom: The 78L33 requires a minimum dropout headroom of ~1.7V to 2.0V. Maintain an input voltage of at least **5.3V DC** under full load to ensure proper +3.3V regulation.
• Power Dissipation & Thermal Limits: Calculate package dissipation using Pd = (Vin - Vout) × Iout. In a TO-92 package without a heatsink, keep total power dissipation under **300mW to 400mW** to prevent the IC from overheating. For higher input voltages (e.g., 24V), limit current output accordingly.
• Reverse Diode Protection: If using large capacitive loads on the output where Vout might remain higher than Vin during sudden power-off, place a 1N4148 or 1N4007 diode in reverse across VOUT (Anode) and VIN (Cathode) to protect the internal pass transistor.

Datasheet