onsemi MPSA77

Overview

MPSA77 from Fairchild Semiconductor is a PNP Darlington transistor optimized for high-current-switching applications up to 1.2 A, featuring minimum DC current gain (hFE) of 10,000 at IC = −100 mA and VCE = −5.0 V, −60 V collector-emitter breakdown voltage (V(BR)CES), and TO-92 package. It serves as a high-gain interface device in low-frequency switching circuits such as relay drivers and lamp controls.

For engineers reviewing the MPSA77 datasheet, pinout, applications, or equivalent options, key selection criteria include guaranteed hFE ≥10,000 at −100 mA, VCE(sat) ≤ −1.5 V under same conditions, thermal resistance RθJA = 200 °C/W, and compatibility with standard through-hole PCB layouts using TO-92 footprint.

Technical Context

The MPSA77 implements a monolithic PNP Darlington pair structure with integrated base-emitter resistor network absent-requiring external base drive control. Its high hFE enables direct microcontroller GPIO-level switching without additional pre-driver stages.

It operates within −55 °C to +150 °C junction temperature range, supports continuous collector current up to −1.2 A, and exhibits fT = 100 MHz at IC = −10 mA, confirming suitability for audio-frequency and DC-coupled switching-not RF or high-speed digital applications.

Key Specifications

Pinout & Package

Package: TO-92 - standard 3-lead through-hole plastic package with 0.1" lead pitch, compatible with manual soldering and wave soldering processes.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar PNP Darlington transistor applications.

Compared with MPSA92 and BC639, the MPSA77 uniquely delivers Darlington-level gain (hFE ≥10,000) in a TO-92 package at −60 V rating-making it optimal for microcontroller-driven, low-power-consumption switching where base current is constrained.

Availability

MPSA77 is available at Aetrix Electronics and suitable for relay driver circuits, lamp dimming controls, DC motor direction modules, and industrial sensor interfaces requiring stable component supply and long-term obsolescence management.

Supply support for MPSA77 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 was a U.S.-based semiconductor company specializing in power management, analog, and discrete devices before its acquisition by ON Semiconductor in 2016.

The MPSA77 belongs to Fairchild's general-purpose bipolar transistor family designed for cost-sensitive, high-reliability industrial and consumer switching applications where high DC gain and rugged voltage ratings are essential.

FAQ

What is the maximum continuous collector current rating for the MPSA77?

The MPSA77 has a maximum continuous collector current (IC) rating of −1.2 A at Ta = 25°C. Derating applies above 25°C ambient per the 5.0 mW/°C thermal coefficient. This rating assumes proper heatsinking and PCB copper area; actual achievable current depends on layout and ambient conditions. The MPSA77 datasheet specifies this value under steady-state DC conditions-not pulsed operation.

Does the MPSA77 include an internal base-emitter resistor?

No, the MPSA77 does not integrate any base-emitter resistor. It is a bare PNP Darlington transistor requiring external base current limiting. Unlike digital transistors (e.g., MMBT2222A with built-in resistors), the MPSA77 gives full design control over base drive but mandates careful calculation of RB to ensure reliable saturation without overdriving. This behavior is confirmed in the "On Characteristics" section of the MPSA77 datasheet.

Can the MPSA77 be used as a direct replacement for the MPSA92?

The MPSA77 and MPSA92 share the same TO-92 package and pinout (E-B-C), but they differ significantly in gain and saturation performance. While physically interchangeable, the MPSA77 offers hFE ≥10,000 versus MPSA92's hFE ≥75-so substituting MPSA77 for MPSA92 may cause excessive base current draw or unintended oscillation if the original circuit relies on lower gain. The MPSA77 is not a drop-in functional replacement without circuit review.

What is the thermal resistance junction-to-ambient (RθJA) for the MPSA77 in TO-92?

The MPSA77 has a specified RθJA of 200 °C/W when mounted on a standard FR-4 PCB with minimal copper. This value assumes natural convection cooling and no added heatsink. At 25°C ambient, the device dissipates up to 625 mW; above that temperature, derating begins at 5.0 mW/°C. These thermal parameters are measured per JEDEC standards and published in the MPSA77 Rev. B1 datasheet.

Is the MPSA77 suitable for high-frequency switching applications?

No, the MPSA77 is not intended for high-frequency switching. Its fT = 100 MHz reflects small-signal bandwidth-not switching speed-and its Darlington structure introduces significant storage time delay. Measured turn-off time exceeds 1 µs, making it unsuitable for PWM above ~20 kHz. The MPSA77 is optimized for DC and audio-frequency (<1 kHz) switching, such as relay actuation and lamp control-not SMPS or Class-D amplifier output stages.