onsemi MC7905CT

Overview

MC7905CT from Fairchild Semiconductor is a three-terminal fixed negative voltage regulator delivering −5.0 V ±4% output at up to 1 A, featuring internal thermal overload protection, short-circuit protection, and safe operating area compensation. It operates with input voltages down to −35 V and supports industrial temperature range (0°C to +125°C), commonly used in dual-rail power supplies for op-amp circuits and analog signal conditioning.

For engineers reviewing the MC7905CT datasheet, pinout, applications, or equivalent options, key selection criteria include guaranteed −5 V regulation tolerance, TO-220 package thermal performance (R_θJC = 5°C/W), dropout voltage ≤2 V at 1 A, ripple rejection ≥54 dB at 120 Hz, and load regulation ≤100 mV across 5 mA–1.5 A.

Technical Context

The MC7905CT implements a monolithic PNP pass transistor architecture with built-in current limiting, thermal shutdown, and SOA compensation-enabling robust operation without external protection circuitry. Its feedback loop uses an internal voltage reference and resistive divider to maintain stable −5 V output under varying line (−7 V to −20 V) and load (5 mA to 1 A) conditions.

Designed for fixed-output negative regulation, it requires only two external capacitors: 2.2 µF input (solid tantalum) and 1 µF output for stability. Ripple rejection of 54–60 dB at 120 Hz and low output noise (40 µV RMS, 10 Hz–100 kHz) make it suitable for noise-sensitive analog subsystems.

Key Specifications

Pinout & Package

MC7905CT is housed in a through-hole TO-220 package with standard 3-pin configuration and integrated heat slug. The case is electrically connected to Pin 1 (GND), requiring isolation when mounted to a heatsink.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar negative voltage regulation applications.

Compared with LM7905CT, MC7905CT offers identical functionality and performance but originates from Fairchild (now ON Semiconductor); versus MC7905ACT, it trades ±2% tolerance for broader availability and lower cost in non-critical regulation roles.

Availability

MC7905CT is available at Aetrix Electronics and suitable for industrial control systems, analog sensor interfaces, and dual-rail op-amp power supplies requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for MC7905CT 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

Fairchild Semiconductor (now part of ON Semiconductor) is a global leader in power management and analog ICs, known for rugged, industry-standard linear regulators and discrete power devices.

The MC79XX series was designed specifically for reliable fixed negative voltage regulation in industrial, automotive, and legacy equipment-emphasizing fault resilience, thermal robustness, and drop-in compatibility with LM79XX parts.

FAQ

What is the maximum input voltage rating for the MC7905CT?

The MC7905CT has an absolute maximum input voltage rating of −35 V. Operation beyond this value risks permanent damage. For reliable regulation, the recommended input range is −7 V to −20 V-ensuring sufficient headroom above the 2 V dropout voltage while maintaining thermal safety at 1 A load. Always verify input ripple and transient spikes remain within this limit in final PCB layout.

Does the MC7905CT require external capacitors, and what values are specified?

Yes, the MC7905CT requires two external capacitors: a 2.2 µF solid tantalum capacitor on the input (Pin 2) and a 1 µF solid tantalum capacitor on the output (Pin 3). These are mandatory for stability per the datasheet. If aluminum electrolytic capacitors are substituted, their values must be increased tenfold (e.g., 10 µF output) to compensate for higher ESR, and a 1N4001 diode should be added from input to output to prevent reverse-current damage during input shorts.

How does thermal protection work in the MC7905CT?

The MC7905CT integrates thermal shutdown circuitry that disables the output pass transistor when junction temperature exceeds approximately 175°C. This protects the device during sustained overload, inadequate heatsinking, or ambient temperature extremes. Once the die cools by ~20°C, regulation automatically resumes-no manual reset is needed. R_θJC = 5°C/W means a properly mounted heatsink can dissipate >15 W before triggering shutdown at 1 A load.

Can the MC7905CT be used in parallel for higher current output?

No, the MC7905CT is not designed for parallel operation. Its output voltage tolerance (±4%) and load regulation (≤100 mV) cause unequal current sharing between units, risking thermal runaway in one device. For >1 A requirements, use a single higher-current regulator (e.g., MC7912CT with external pass transistor) or switch to a switching solution-never parallel MC7905CT units without active current-balancing circuitry.

What is the significance of the 'CT' suffix in MC7905CT?

The 'CT' suffix in MC7905CT denotes the TO-220 package variant with standard lead finish and industrial temperature range (0°C to +125°C). It distinguishes this version from surface-mount (e.g., MC7905CD2TR) or extended-temperature variants. All MC7905CT units share identical electrical specifications, pinout, and thermal characteristics-ensuring direct mechanical and functional interchangeability across authorized distributors and manufacturing lots.