onsemi 2N6426

Overview

2N6426 from Fairchild Semiconductor is an NPN Darlington transistor optimized for high-current-switching applications requiring extremely high DC current gain (h_FE up to 300,000) at collector currents up to 1.0 A, with V_CEO = 40 V, I_C = 1.2 A continuous, and TO-92 package. It serves as a low-input-drive power switch in relay drivers, lamp controllers, and small-motor interfaces.

For engineers reviewing the 2N6426 datasheet, pinout, applications, or equivalent options, key selection criteria include verified h_FE performance at 500 mA, V_CE(sat) ≤ 1.5 V under 0.5 mA base drive, thermal resistance R_θJA = 200 °C/W, and TO-92 mechanical compatibility for through-hole PCB layouts.

Technical Context

The 2N6426 implements a monolithic NPN Darlington pair architecture-two cascaded NPN transistors on a single die-to achieve ultra-high DC current gain while maintaining manageable base drive requirements. Its design targets linear and saturated switching modes with defined saturation voltages at multiple operating points.

It operates across –55°C to +150°C junction temperature range and is characterized with strict OFF-state leakage limits (e.g., I_CEO ≤ 1.0 µA at V_CE = 25 V), enabling reliable operation in industrial control environments where ambient temperatures and leakage sensitivity are critical.

Key Specifications

Pinout & Package

2N6426 is housed in a standard TO-92 plastic package with straight leads and no lead clip. Pin identification follows JEDEC TO-92 configuration: viewed from flat side with leads down, left-to-right pin order is Emitter (E), Base (B), Collector (C).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA14 and ULN2003A, the 2N6426 offers higher continuous current capability and verified h_FE performance at 500 mA, making it optimal for single-load, high-gain, through-hole switching where discrete layout and thermal management are prioritized over integration.

Availability

2N6426 is available at Aetrix Electronics and suitable for relay driver circuits, lamp control systems, and small DC motor interfaces requiring stable component supply, long-lifecycle support, and consistent TO-92 mechanical form factor.

Supply support for 2N6426 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 2N6426 belongs to Fairchild's legacy discrete power transistor family designed specifically for cost-sensitive, high-reliability industrial switching applications demanding high DC gain and robust thermal performance in TO-92 packaging.

FAQ

What is the maximum continuous collector current rating for the 2N6426?

The 2N6426 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 5.0 mW/°C thermal derating curve. Actual usable current depends on PCB copper area, ambient temperature, and duty cycle - sustained operation near 1.0 A requires attention to R_θJA = 200 °C/W and thermal layout. The 2N6426 datasheet confirms this rating under steady-state conditions.

Does the 2N6426 have built-in base-emitter resistor networks?

No, the 2N6426 is a bare NPN Darlington transistor without integrated base resistors. It requires an external current-limiting resistor between the driving source and the base terminal to set appropriate I_B. This distinguishes it from "digital transistors" like the NSV12201 or MMDT3904, which embed resistors. The 2N6426 provides full design flexibility for base biasing but mandates explicit external resistor selection - confirmed by its electrical characteristics table and schematic symbol in the Fairchild datasheet.

What is the typical V_CE(sat) of the 2N6426 at 500 mA collector current?

The typical V_CE(sat) of the 2N6426 is 1.5 V at I_C = 500 mA and I_B = 0.5 mA, with a maximum guaranteed value of 1.5 V under those test conditions. This saturation voltage is measured with the device fully driven into hard saturation and directly impacts conduction losses - for example, 0.75 W dissipation at 500 mA. The 2N6426 datasheet specifies this parameter in the ON CHARACTERISTICS section with pulse-test conditions (≤300 µs, ≤2% duty cycle).

Can the 2N6426 replace the MPSA14 in existing designs?

The 2N6426 can replace the MPSA14 only if the application requires higher current handling (up to 1.2 A vs. 500 mA) and higher h_FE at elevated I_C; however, pinout is identical (TO-92, E-B-C), and both share Process 05. Voltage ratings match (V_CEO = 40 V), but the 2N6426's higher power dissipation (625 mW vs. 625 mW) and thermal resistance require verification of board-level heatsinking. The 2N6426 datasheet explicitly references MPSA14 for characteristics, confirming functional alignment within shared process constraints.

Is the 2N6426 suitable for PWM motor speed control?

The 2N6426 is not recommended for high-frequency PWM motor control due to its relatively slow switching speeds - small-signal h_fe is specified only at 1 kHz, and no f_T, t_on, or t_off data is provided. It is optimized for DC or low-frequency (<100 Hz) on/off switching. For PWM, consider faster alternatives like the FZT651 or ZTX653. The 2N6426 datasheet emphasizes DC gain and saturation behavior, not dynamic performance - confirming its role as a linear/saturated switch, not a switching regulator element.