onsemi MMBT6427

Overview

MMBT6427 from Fairchild Semiconductor is an NPN Darlington transistor optimized for high-current-gain switching applications up to 1.2 A continuous collector current, with V_CEO = 40 V and h_FE ≥ 10,000 at I_C = 10 mA. It is commonly used in relay drivers, lamp drivers, and low-frequency power switching circuits where minimal base drive is required.

For engineers reviewing the MMBT6427 datasheet, pinout, applications, or equivalent options, key selection criteria include guaranteed h_FE > 10 k at low I_C, V_CE(sat) ≤ 1.5 V at I_C = 500 mA, thermal resistance R_θJA = 357 °C/W in SOT-23, and compatibility with TO-92 and SOT-23 footprints.

Technical Context

The MMBT6427 implements a monolithic NPN Darlington pair architecture, delivering ultra-high DC current gain (h_FE up to 200,000) while maintaining V_CE(sat) ≤ 1.5 V at I_C = 500 mA and I_B = 0.5 mA. Its structure supports low-base-drive operation in saturated-switching configurations.

It features breakdown voltages of V_CEO = V_CBO = 40 V and V_EBO = 12 V, with leakage currents ICEO ≤ 1.0 µA and ICBO ≤ 50 nA at rated conditions. Thermal performance is specified for both TO-92 (R_θJA = 200 °C/W) and SOT-23 (R_θJA = 357 °C/W) packages under defined PCB mounting conditions.

Key Specifications

Pinout & Package

MMBT6427 is available in both TO-92 and SOT-23 packages. The SOT-23 variant uses standard 3-pin configuration with emitter, base, and collector assigned to pins 1, 2, and 3 respectively, marked "1V" on the top surface. TO-92 version follows conventional C-B-E lead order (collector–base–emitter) when viewed with flat side facing user and leads down.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MMBT6428 and BC817-40, the MMBT6427 uniquely balances ultra-high h_FE (>10 k), 40 V breakdown, and 1.2 A current capability in a compact SOT-23 package-making it the preferred choice for low-power-control-to-high-power-load interfacing where base drive current is severely constrained.

Availability

MMBT6427 is available at Aetrix Electronics and suitable for relay drivers, lamp controllers, DC motor starters, and industrial sensor interfaces requiring stable component supply across production lifecycles.

Supply support for MMBT6427 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 leading designer and manufacturer of power management, analog, and discrete semiconductors, acquired by ON Semiconductor in 2016; its legacy product lines remain widely deployed and supported.

The MMBT6427 belongs to Fairchild's general-purpose Darlington transistor family, engineered specifically for high-gain, low-base-drive switching in industrial control, appliance, and automotive subsystems.

FAQ

What is the maximum continuous collector current rating for the MMBT6427?

The MMBT6427 has a maximum continuous collector current (I_C) rating of 1.2 A at T_A = 25°C. Derating applies above 25°C per the specified thermal resistance (R_θJA = 357 °C/W for SOT-23). Actual usable current depends on PCB layout, ambient temperature, and heatsinking. The MMBT6427 must be operated within its Safe Operating Area (SOA) limits to avoid secondary breakdown.

Does the MMBT6427 have a documented pinout for the SOT-23 package?

Yes-the MMBT6427 in SOT-23 uses standard pin assignment: Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector, with marking "1V" on the top surface. This matches JEDEC MO-178 and Fairchild's official SOT-23 tape-and-reel documentation. The TO-92 variant uses C-B-E order (lead 1 = collector) when viewed with flat side facing forward and leads pointing downward.

What is the typical V_CE(sat) of the MMBT6427 at I_C = 500 mA?

The MMBT6427 exhibits a typical V_CE(sat) of 1.5 V at I_C = 500 mA and I_B = 0.5 mA, with a maximum of 1.8 V under those conditions. This saturation voltage reflects the two-V_BE drop inherent to Darlington topology and directly impacts conduction loss and thermal performance in high-current switching applications using the MMBT6427.

Can the MMBT6427 replace the MPSA14 in existing designs?

The MMBT6427 shares identical electrical characteristics with the MPSA14 per Fairchild's datasheet cross-reference, including V_CEO = 40 V, h_FE ≥ 10,000, and pin-compatible SOT-23/TO-92 packaging. However, the MMBT6427 is explicitly qualified for Process 05 and may exhibit tighter parameter distributions; system validation is recommended before drop-in replacement in safety-critical MMBT6427 deployments.

Is the MMBT6427 suitable for PWM motor control applications?

The MMBT6427 is not optimized for high-frequency PWM motor control due to its Darlington structure, which introduces slower turn-off times and no specified f_T or switching parameters. It is best suited for DC or low-frequency (<1 kHz) switching. For PWM applications above 5 kHz, a single NPN like BC817-40 or MOSFET-based solution is more appropriate than the MMBT6427.