onsemi MC7908CTG

Overview

MC7908CTG from onsemi is a fixed-output negative voltage regulator delivering −8.0 V at up to 1.0 A, featuring internal thermal shutdown, short-circuit current limiting, and safe-area compensation for rugged operation in industrial power supplies. It requires no external components for basic regulation and maintains stable output under load currents from 5 mA to 1.0 A with ≤80 mV load regulation.

For engineers reviewing the MC7908CTG datasheet, pinout, applications, or equivalent options, key selection factors include its −8.0 V nominal output, TO-220 package with heatsink-connected Pin 2, dropout voltage of 1.3 V at 1.0 A, ripple rejection of 62 dB at 120 Hz, and operating junction temperature range of 0°C to +125°C.

Technical Context

The MC7908CTG implements a monolithic bipolar pass transistor architecture with integrated protection circuitry. Its internal safe-area compensation dynamically reduces short-circuit current as the input-output differential increases, preventing second breakdown during fault conditions.

Thermal overload protection activates at +150°C junction temperature, and short-circuit limiting holds peak output current below 1.8 A under typical conditions. The device operates without external capacitors in low-noise, low-current applications but recommends 0.33 µF input and 1.0 µF output bypassing for stability with long trace lengths or large load capacitance.

Key Specifications

Pinout & Package

MC7908CTG uses the TO-220 package (Case 221AB), with the metal tab (heatsink surface) electrically connected to Pin 2 (Input). This configuration requires isolation hardware when mounting to grounded heat sinks.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM337T and MC7908CD2TR4G, the MC7908CTG offers lowest system cost for fixed −8.0 V needs via zero-component regulation and TO-220 through-hole compatibility, while maintaining identical core protection features and thermal robustness.

Availability

MC7908CTG is available at Aetrix Electronics and suitable for industrial control systems, test equipment power supplies, and analog signal chain designs requiring stable component supply and long-term manufacturability.

Supply support for MC7908CTG 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier focused on energy-efficient electronics, serving automotive, industrial, cloud, and IoT markets with discrete, analog, and power management solutions.

The MC7900 series was designed specifically to complement the MC7800 positive regulators, providing rugged, fixed-output negative voltage regulation for dual-rail analog systems and legacy logic families requiring −5 V to −24 V supplies.

FAQ

What is the guaranteed output voltage tolerance for MC7908CTG over temperature?

The MC7908CTG guarantees −7.6 V to −8.4 V output voltage across its full operating junction temperature range of 0°C to +125°C, corresponding to ±4% tolerance at 1.0 A load and specified input conditions. This is confirmed in the "MC7908C" electrical characteristics table on page 4 of the official datasheet, where VO min/max values are explicitly listed as −7.6 V and −8.4 V under −10.5 Vdc ≥ VI ≥ −23 Vdc, 5.0 mA ≤ IO ≤ 1.0 A, and P ≤ 15 W.

Can MC7908CTG be used without input or output capacitors?

Yes, the MC7908CTG can operate without external capacitors in low-current, low-noise applications with short interconnects. However, the datasheet recommends a 0.33 µF input capacitor when mounted remotely from the power supply filter and a 1.0 µF output capacitor to improve transient response and stability-especially with large load capacitance or long PCB traces. These values are specified in the "Standard Application" section on page 1.

What is the maximum allowable input voltage for MC7908CTG?

The absolute maximum input voltage for MC7908CTG is −40 Vdc, as stated in the "Maximum Ratings" table on page 2 of the datasheet. This applies when the output voltage is −24 V; for the −8.0 V version, the recommended maximum is −23 Vdc to maintain safe power dissipation and avoid exceeding the 15 W limit under worst-case conditions.

How does the thermal shutdown feature protect MC7908CTG?

The MC7908CTG incorporates internal thermal overload protection that disables the output stage when junction temperature reaches +150°C. This shutdown is fully automatic and self-resetting: once the die cools below the hysteresis threshold (~140°C), regulation resumes without external intervention. This mechanism prevents irreversible damage during sustained overload or inadequate heatsinking, as documented in the "Applications Information" section on page 9.

Is MC7908CTG pin-compatible with other MC7900 series regulators?

Yes, all MC7900 series regulators-including MC7905CTG, MC7912CTG, and MC7915CTG-share identical TO-220 pinout (Pin 1 = Ground, Pin 2 = Input, Pin 3 = Output) and mechanical footprint. This allows direct substitution within the same family for different output voltages, provided input voltage headroom and thermal design accommodate the new dropout and power dissipation requirements.