STMicroelectronics L78L33ABD

Overview

L78L33ABD from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 3.3 V output at up to 100 mA, featuring thermal overload and short-circuit protection, no external components required, ±4% output voltage tolerance, and a 1.7 V dropout voltage. It serves as a local on-card regulator for noise-sensitive microcontroller I/O rails in industrial control modules.

For engineers reviewing the L78L33ABD datasheet, L78L33ABD pinout, L78L33ABD application, or L78L33ABD equivalent, this page provides verified electrical characteristics, TO-92 package details, thermal resistance data (R_thJA = 200 °C/W), quiescent current (6 mA typ. at 25 °C), and real-world use cases in embedded power domains requiring stable low-current biasing.

Technical Context

The L78L33ABD employs internal current limiting and thermal shutdown circuitry, enabling robust operation without external protection components. Its architecture supports direct replacement of Zener diode–resistor networks with lower quiescent current (6 mA) and reduced output noise (40 µV RMS, 10 Hz–100 kHz).

It operates across an input voltage range of 5.3 V to 20 V, maintains regulation over –40 °C to +125 °C junction temperature, and delivers 3.3 V ±4% output under load currents from 1 mA to 100 mA - with line regulation ≤100 mV and load regulation ≤30 mV under specified conditions.

Key Specifications

Pinout & Package

Supplied in TO-92 package (JEDEC TO-226AA), with 3.3 mm pitch, axial lead configuration, and through-hole mounting. Thermal resistance is R_thJA = 200 °C/W (no heatsink) and R_thJC = 15 °C/W.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fixed-output linear regulator applications.

Compared with LM78L33ACZ, L78L33ABD offers wider operating temperature (–40 to 125 °C vs. 0–70 °C) and tighter output tolerance (±4% vs. ±5%). Versus TLV73333PDBVR, it trades lower quiescent current for integrated protection and zero-external-component simplicity - critical for reliability-focused industrial designs.

Availability

L78L33ABD is available at Aetrix Electronics and suitable for industrial sensor nodes, MCU I/O rail regulation, legacy system upgrades, and low-power IoT edge nodes requiring stable component supply with long-term manufacturability assurance.

Supply support for L78L33ABD includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The L78L series was developed specifically for cost-sensitive, space-constrained embedded applications requiring rugged, drop-in fixed-voltage regulation - emphasizing reliability, ease of use, and compatibility with legacy through-hole assembly processes.

FAQ

What is the minimum input voltage required for L78L33ABD to maintain regulation?

The L78L33ABD requires a minimum input voltage of 5.3 V to sustain 3.3 V output under full 100 mA load, based on its 1.7 V dropout voltage specification. At lighter loads (e.g., 10 mA), regulation holds down to ~5.0 V input, but design margin should retain ≥5.3 V to ensure stability across temperature and line variations.

Can L78L33ABD be used in parallel to increase output current?

No - the L78L33ABD lacks current-sharing capability and has no output current balancing mechanism. Parallel connection risks thermal runaway due to mismatched output voltages and unequal current division. For >100 mA, use a single higher-current regulator (e.g., L78M33) or external pass transistor configuration per datasheet Figure 12.

Is a heat sink required for continuous 100 mA operation?

A heat sink is not required for 100 mA operation at ambient temperatures ≤50 °C with standard TO-92 PCB layout (≥1 cm² copper pour). At 100 mA with 12 V input, power dissipation is ~870 mW; junction temperature rise is ~174 °C above ambient (R_thJA = 200 °C/W), exceeding 125 °C max. Derating or added copper is mandatory above 40 °C ambient.

Does L78L33ABD support reverse-polarity input protection?

No - the L78L33ABD has no internal reverse-voltage protection. Applying negative voltage to VIN relative to GND can damage the IC. External protection (e.g., series Schottky diode or PMOS FET) is required in systems prone to incorrect battery insertion or field wiring errors.