STMicroelectronics L78L33CD

Overview

L78L33CD from STMicroelectronics is a three-terminal positive linear voltage regulator delivering a fixed 3.3 V output at up to 100 mA, featuring internal current limiting, thermal overload protection, and short-circuit protection. It requires no external components and is specified for ±4% output tolerance (C-grade), with 1.7 V dropout voltage and 40 µV RMS output noise (10 Hz–100 kHz). It serves as a low-noise local power supply for microcontroller I/O rails and sensor biasing in industrial control modules.

For engineers reviewing the L78L33CD datasheet, L78L33CD pinout, L78L33CD application, or L78L33CD equivalent, this page provides verified technical context, package-specific thermal data, real-world load/line regulation behavior, and validated alternative options for 3.3 V low-current regulation in space-constrained designs.

Technical Context

The L78L33CD implements a monolithic silicon-based series pass regulator architecture with built-in foldback current limiting and thermal shutdown circuitry. Its internal reference and error amplifier maintain output regulation across input voltages from 5.3 V to 20 V and junction temperatures from 0 °C to 125 °C.

It operates without external capacitors for basic functionality but specifies 0.33 µF input and 0.1 µF output ceramic capacitors for stability and transient response optimization. The device's 1.7 V dropout enables operation from 5 V rail inputs while sustaining full 100 mA load under worst-case conditions.

Key Specifications

Pinout & Package

Supplied in TO-92 package (JEDEC TO-226AA), with molded plastic case, axial leads, and standard through-hole mounting. Pin 1 = V_OUT, Pin 2 = GND, Pin 3 = V_IN (top view).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM78L33ACZ, L78L33CD offers 30× lower output noise and 30% lower I_Q; compared with MCP1700-3302E/TO, it trades ultra-low I_Q for proven ruggedness in industrial environments and TO-92 compatibility.

Availability

L78L33CD is available at Aetrix Electronics and suitable for industrial sensor interfaces, microcontroller I/O power, IoT node subsystems, and legacy system voltage translation requiring stable component supply and long-term manufacturability.

Supply support for L78L33CD 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 as a robust, low-cost family of fixed-voltage linear regulators targeting cost-sensitive, space-constrained applications requiring high reliability and minimal external components - especially in industrial control, instrumentation, and legacy system upgrades.

FAQ

What is the minimum input voltage required for L78L33CD to regulate at full 100 mA?

The L78L33CD requires a minimum input voltage of 5.3 V to sustain 3.3 V output at 100 mA load, based on its 1.7 V dropout specification and guaranteed performance across temperature. At 25 °C, regulation holds down to 5.0 V, but 5.3 V ensures compliance across the full 0–125 °C operating range per datasheet Table 12.

Can L78L33CD be used with ceramic output capacitors?

Yes - the L78L33CD is stable with 0.1 µF ceramic output capacitors, as confirmed in ST's test circuits (Figure 3) and electrical characteristics tables. Unlike older 78xx regulators, it does not require ESR-based damping and benefits from low-ESR ceramics for improved transient response and reduced board area.

How does thermal performance differ between TO-92 and SO-8 packages for L78L33CD?

The TO-92 package has R_thJA = 200 °C/W (no heatsink), limiting continuous 100 mA operation to ambient ≤50 °C. The SO-8 variant (not this part number) achieves R_thJA = 55 °C/W with 6 cm² copper pour, enabling full-rated current up to 85 °C ambient - a critical distinction for enclosed industrial enclosures.

Is L78L33CD pin-compatible with other L78Lxx variants?

Yes - all L78Lxx devices (e.g., L78L05, L78L12) share identical TO-92 pinout: Pin 1 = V_OUT, Pin 2 = GND, Pin 3 = V_IN. This enables direct substitution across output voltages in existing layouts, provided input voltage headroom and thermal design accommodate the specific variant's dropout and power dissipation.