onsemi MC7908ACTG

Overview

MC7908ACTG from onsemi is a fixed-output negative linear 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 output stability with input ripple up to −10.5 V to −23 V.

For engineers reviewing the MC7908ACTG datasheet, pinout, applications, or equivalent options, key selection criteria include dropout voltage (1.3 V at 1.0 A), load regulation (26 mV over 5–1.5 A), ripple rejection (62 dB at 120 Hz), and TO−220 package thermal resistance (θ_JA = 65 °C/W).

Technical Context

The MC7908ACTG implements a monolithic bipolar pass transistor with integrated protection circuitry, including current-limiting sense networks and thermal foldback that reduces output current as junction temperature approaches +150 °C. Its internal safe-area compensation dynamically adjusts base drive to prevent secondary breakdown under high V_CE stress.

Designed as a complement to the MC7800 series, it shares identical pinout and thermal design rules with positive counterparts but operates with reversed polarity-ground referenced at Pin 1, input at Pin 2, and regulated negative output at Pin 3. Input bias current remains stable at 4.3 mA typical across its operating range.

Key Specifications

Pinout & Package

MC7908ACTG uses the TO−220 package (Case 221AB), with heatsink surface electrically connected to Pin 2 (Input). The device has three terminals: Pin 1 (Ground), Pin 2 (Input), Pin 3 (Output).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM7908CT and MC7908CTG, the MC7908ACTG offers superior output accuracy (±2% vs ±4%), lower quiescent current, and guaranteed operation up to +125°C-making it optimal for industrial-grade analog power rails where long-term drift and thermal margin are critical.

Availability

MC7908ACTG is available at Aetrix Electronics and suitable for industrial sensor interfaces, dual-rail op-amp supplies, and legacy MECL logic systems requiring stable component supply and long-lifecycle support.

Supply support for MC7908ACTG 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 manufacturer specializing in energy-efficient power management, analog, and sensor solutions for automotive, industrial, and cloud infrastructure markets.

The MC7900 Series was designed specifically to provide robust, drop-in complementary negative regulators for legacy and new designs using the widely adopted MC7800 positive regulator family-enabling dual-rail systems with matched thermal and electrical behavior.

FAQ

What is the maximum input voltage rating for the MC7908ACTG?

The MC7908ACTG supports a maximum input voltage of −35 Vdc for output voltages between −5.0 V and −18 V. Since the MC7908ACTG delivers −8.0 V, its absolute maximum input is −35 V. Exceeding this risks permanent damage, even briefly. Always maintain at least 2.0 V differential between input and output under worst-case ripple conditions.

Does the MC7908ACTG require input and output capacitors for stable operation?

Yes-the MC7908ACTG requires a 0.33 µF input bypass capacitor (tantalum or low-ESR film) placed directly across Pins 1 and 2, and a 1.0 µF output capacitor (electrolytic or tantalum) across Pins 1 and 3. These stabilize transient response and prevent oscillation, especially when traces exceed 2 inches or load capacitance exceeds 10 µF. Omission may cause regulation failure or thermal shutdown.

Can the MC7908ACTG be used in parallel to increase output current?

No-MC7908ACTG devices must not be paralleled. Unlike some regulators with current-sharing features, the MC7908ACTG lacks built-in balancing circuitry. Minor output voltage mismatches (±0.3 V) will cause one unit to carry disproportionate current, leading to thermal runaway and premature failure. For higher current, use a single MC7908ACTG with external pass transistor per Figure 9 in the datasheet.

What is the thermal resistance and power dissipation limit of the MC7908ACTG in TO−220 package?

The MC7908ACTG in TO−220 (Case 221AB) has θ_JA = 65 °C/W and θ_JC = 5.0 °C/W. With no heatsink, its maximum power dissipation is ~1.5 W at +25°C ambient. With a 5°C/W heatsink, PD(max) rises to 15 W. Derate linearly above +25°C ambient: at +70°C, max dissipation drops to ~8.3 W before reaching T_J = +150°C.

Is the MC7908ACTG pin-compatible with other MC7900-series regulators?

Yes-MC7908ACTG is fully pin-compatible with all MC7900-series variants (e.g., MC7905ACTG, MC7912ACTG) in the same TO−220 package. Pin 1 is Ground, Pin 2 is Input, Pin 3 is Output across the entire family. This allows direct substitution in existing layouts when changing output voltage, provided input voltage and thermal design accommodate the new dropout and power requirements.