STMicroelectronics LM323K

Overview

LM323K from STMicroelectronics is a three-terminal positive voltage regulator delivering a fixed 5 V output with 3 A continuous load current capability, internal current and thermal limiting, typical output impedance of 0.01 Ω, and minimum input voltage of 7.5 V. It is used in high-current power supplies for industrial control systems requiring stable 5 V rail generation under varying load and temperature conditions.

For engineers reviewing the LM323K datasheet, LM323K pinout, LM323K application, or LM323K equivalent, key selection considerations include guaranteed 5 V output tolerance (±5% over full temperature and load range), internal short-circuit current limit (4–5 A at 7.5 V input), thermal shutdown activation at 125 °C junction temperature, and TO-3 package thermal resistance (2 °C/W junction-to-case).

Technical Context

The LM323K implements a monolithic bipolar linear regulator architecture with built-in foldback current limiting and thermal shutdown circuitry. Its regulation loop maintains output stability across 0–3 A load and 7.5–15 V input while sustaining ≤100 mV load regulation and ≤25 mV line regulation at 25 °C.

It operates without external compensation into resistive loads and achieves 40 µV_RMS output noise (10 Hz–100 kHz) and ≥50 dB ripple rejection at 120 Hz. Junction temperature is monitored continuously, triggering shutdown before exceeding 125 °C.

Key Specifications

Pinout & Package

The LM323K is housed in a hermetically sealed TO-3 metal can package with three terminals: Input, Output, and Ground. The case is electrically connected to the output terminal, requiring insulated mounting hardware when output is not at chassis ground.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM323K, LM338K offers voltage adjustability at the cost of initial 5 V accuracy and added external components, while LT1083CP trades TO-3 ruggedness and ultra-low noise for SMT manufacturability and wider input range - neither matches LM323K's combination of fixed 5 V precision, 3 A capability, and hermetic metal-can reliability in harsh environments.

Availability

LM323K is available at Aetrix Electronics and suitable for industrial PLC power supplies, test equipment main rails, motor drive logic supplies, and legacy embedded system rails requiring stable component supply with long-term obsolescence mitigation.

Supply support for LM323K 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 LM323 series belongs to ST's legacy linear regulator product line, engineered specifically for high-reliability, high-current industrial power conversion where simplicity, ruggedness, and thermal resilience outweigh switching efficiency requirements.

FAQ

What is the maximum allowable power dissipation for LM323K under continuous operation?

The LM323K is rated for 30 W maximum power dissipation under specified thermal conditions. This limit applies only when junction temperature remains within 0–125 °C, and requires use of a heatsink capable of maintaining junction-to-ambient thermal resistance ≤35 °C/W (per TO-3 R_thJA spec). Exceeding 30 W triggers internal thermal shutdown.

Can LM323K operate without an output capacitor?

Yes, the LM323K is internally compensated and stable with no output capacitor when driving purely resistive loads, as confirmed in ST's datasheet Figure 13 and Section 6. However, adding a 10–100 µF electrolytic capacitor improves transient response and reduces output impedance at high frequencies - recommended for dynamic loads like microcontrollers or digital I/O banks.

Is the LM323K pin-compatible with standard TO-3 voltage regulators like the 7805?

No. While both use TO-3 packages, LM323K has Input–Output–Ground pinout (Pin 1–2–3), whereas 7805 variants use Input–Ground–Output. Mounting the LM323K in a 7805 footprint will cause immediate short-circuit failure. Physical pin alignment and terminal assignment must be verified using ST's mechanical drawing P003C/C.

Does LM323K support adjustable output voltage configurations?

No - the LM323K is a fixed 5 V output device with factory-trimmed internal feedback. ST does not specify or characterize it for adjustable operation. For adjustable 3 A regulation, ST recommends the LM338K (5 A, adjustable), which shares the TO-3 package and thermal design approach but uses external resistors to set output voltage.