onsemi MPSA12

Overview

MPSA12 from ON Semiconductor (formerly Fairchild) is an NPN Darlington transistor optimized for high-current-switching applications requiring extreme DC current gain (h_FE = 20,000 at I_C = 10 mA, V_CE = 5 V), with V_CEO = 20 V, I_C = 1.2 A continuous, and TO-92 package-commonly used in relay drivers, lamp drivers, and low-frequency power switching circuits.

For engineers reviewing the MPSA12 datasheet, pinout, applications, or equivalent options, key selection considerations include its Darlington architecture enabling microamp-level base drive, saturation voltage of 1.0 V at I_C/I_B = 10 mA/0.01 mA, thermal resistance R_θJA = 200 °C/W, and compatibility with legacy through-hole logic interface designs.

Technical Context

The MPSA12 integrates two cascaded NPN transistors in a monolithic Darlington configuration, delivering ultra-high h_FE while maintaining V_CEO = 20 V and V_CE(sat) = 1.0 V under specified test conditions. Its design targets low-base-drive digital control of moderate-power loads without external gain staging.

Thermal performance is defined by R_θJA = 200 °C/W and R_θJC = 83.3 °C/W, with maximum junction temperature limited to +150 °C. Absolute ratings include V_CBO = V_CEO = 20 V, V_EBO = 10 V, and P_D = 625 mW at T_A = 25 °C, derating linearly above that temperature.

Key Specifications

Pinout & Package

Package: TO-92 - Standard 3-lead through-hole plastic package with 1.27 mm lead pitch, rated for manual assembly and wave soldering. Dimensions conform to JEDEC TO-92 outline.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA13 and MPSA14, the MPSA12 offers the highest gain-to-voltage ratio among TO-92 Darlington transistors, making it optimal for 12–20 V systems where minimal base current is critical-but not suitable where >20 V collector swing is required.

Availability

MPSA12 is available at Aetrix Electronics and suitable for relay driver circuits, lamp control modules, solenoid actuation systems, and legacy logic interface adapters requiring stable component supply and long-term obsolescence support.

Supply support for MPSA12 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

ON Semiconductor is a global semiconductor supplier delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The MPSA12 belongs to ON Semiconductor's legacy general-purpose bipolar transistor product line, designed specifically for cost-sensitive, high-reliability through-hole switching applications in industrial controls and consumer electronics.

FAQ

What is the maximum collector-emitter voltage rating for the MPSA12?

The MPSA12 has a maximum collector-emitter voltage (V_CEO) rating of 20 V, verified per its Absolute Maximum Ratings table at T_A = 25 °C. This value reflects the upper limit before avalanche breakdown occurs with the base open. Exceeding 20 V risks permanent device failure, and the MPSA12 must not be used in circuits where transient or steady-state V_CE exceeds this rating without clamping or derating.

Does the MPSA12 have a built-in base-emitter resistor?

No, the MPSA12 does not include any internal base-emitter resistor. It is a bare Darlington transistor requiring an external base resistor to limit drive current from the controlling source. Unlike digital transistors (e.g., NSM1012MR), the MPSA12 relies on external biasing for proper saturation and thermal stability-confirming its classification as a discrete general-purpose switching transistor.

What is the typical DC current gain (h_FE) of the MPSA12 at 10 mA collector current?

The typical DC current gain (h_FE) of the MPSA12 is 20,000 when measured at V_CE = 5.0 V and I_C = 10 mA, as specified in its Electrical Characteristics table. This value is representative of its Darlington architecture and enables microampere-level base currents to fully saturate the device-making the MPSA12 especially effective in low-drive digital interface applications.

Can the MPSA12 replace the MPSA14 in a circuit?

The MPSA12 cannot directly replace the MPSA14 in all circuits because the MPSA14 has a higher V_CEO rating of 30 V versus 20 V for the MPSA12. In a 24 V system, the MPSA12 would exceed its absolute maximum rating and risk failure. However, in 12 V or lower supply applications where gain and saturation behavior are prioritized, the MPSA12 may serve as a functional substitute-but only after verifying voltage margins and thermal performance in the target design.

What is the thermal resistance junction-to-ambient (R_θJA) for the MPSA12 in TO-92 package?

The thermal resistance junction-to-ambient (R_θJA) for the MPSA12 in its standard TO-92 package is 200 °C/W, as published in the Thermal Characteristics section of its datasheet. This value assumes standard PCB mounting with no heatsink; actual thermal performance will improve with copper pour, airflow, or thermal vias, but sustained power dissipation above ~300 mW requires careful thermal design to avoid exceeding the +150 °C maximum junction temperature.