onsemi 2N5308

Overview

2N5308 from Fairchild Semiconductor is an NPN Darlington transistor in TO-92 package, designed for high-current-switching applications with DC current gain (hFE) of 7,000–70,000 at IC = 2.0mA–100mA, VCE = 5.0V, and maximum continuous collector current of 1.2A. It operates across –55°C to +150°C and supports low-saturation switching in relay drivers and power regulators.

For engineers reviewing the 2N5308 datasheet, pinout, applications, or equivalent options, key selection criteria include verified Darlington gain structure, TO-92 thermal resistance (RθJA = 200°C/W), breakdown voltage ratings (VCEO = VCB0 = 40V), and saturation performance (VCE(sat) = 1.4V @ IC = 200mA, IB = 0.2mA).

Technical Context

The 2N5308 implements a monolithic NPN Darlington pair optimized for high DC current gain at collector currents up to 1.0A, with internal base-emitter resistor network omitted-requiring external base drive control. Its off-state leakage (ICBO ≤ 0.1µA @ 40V, 25°C) and junction temperature range (–55°C to +150°C) support industrial switching environments.

Small-signal parameters confirm bandwidth limitation: hfe drops from 7,000 at 1kHz to 6.0 at 10MHz, and Ccb = 10pF @ VCB = 10V, f = 1MHz-indicating suitability for DC/low-frequency switching rather than RF or high-speed digital use.

Key Specifications

Pinout & Package

2N5308 is housed in a standard TO-92 plastic package with lead spacing matching JEDEC TO-92 outline. The device uses a straight-lead configuration with Emitter (pin 1), Collector (pin 2), and Base (pin 3) as defined in the official Fairchild package drawing.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MPSA14 and ULN2003A, the 2N5308 offers higher VCEO (40V vs. 30V) and broader hFE range (7k–70k), making it preferable for 24V industrial switching where transient margin and gain stability at 100mA are critical-while ULN2003A serves parallel digital I/O needs, not discrete analog switching.

Availability

2N5308 is available at Aetrix Electronics and suitable for relay drivers, DC motor controls, solid-state lamp dimmers, and industrial sensor interfaces requiring stable component supply and long-lifecycle support.

Supply support for 2N5308 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 designer and manufacturer of analog and discrete semiconductors, acquired by ON Semiconductor in 2016. Its legacy products remain widely deployed in industrial and automotive systems.

The 2N5308 belongs to Fairchild's general-purpose bipolar transistor family, developed specifically for high-gain, medium-power linear and switching applications in industrial control, power management, and electromechanical interface circuits.

FAQ

What is the maximum collector current rating for the 2N5308?

The 2N5308 has a maximum continuous collector current (IC) rating of 1.2 A at TA = 25°C. This rating assumes proper heat sinking and derating per the thermal resistance specification (5.0 mW/°C above 25°C). At elevated ambient temperatures or without airflow, actual usable current must be reduced to maintain junction temperature ≤150°C. The 2N5308 datasheet confirms this value under Absolute Maximum Ratings.

Does the 2N5308 include an internal base resistor?

No, the 2N5308 does not incorporate an internal base resistor. It is a bare Darlington transistor requiring external base current limiting-typically a series resistor sized to deliver sufficient IB for target IC while respecting VBE(on) ≈ 1.5 V and power dissipation limits. This distinguishes it from integrated driver types like ULN2003A. Always calculate IB based on hFE min at operating IC when designing with the 2N5308.

What is the typical VCE(sat) of the 2N5308 and under what conditions is it specified?

The 2N5308 specifies VCE(sat) = 1.4 V under test conditions of IC = 200 mA and IB = 0.2 mA at TA = 25°C. This saturation voltage reflects the combined drop across both Darlington emitter-base junctions and the output transistor's channel. It remains stable across the recommended operating range and directly impacts conduction loss in switching applications-making it critical for efficiency calculations in relay or lamp driver designs using the 2N5308.

Can the 2N5308 replace the MPSA14 in existing designs?

The 2N5308 can replace the MPSA14 in many high-voltage applications due to its higher VCEO (40 V vs. 30 V) and broader hFE range (7,000–70,000 vs. 10,000–50,000), but pinout compatibility must be verified: both use TO-92 with E-C-B order (pin 1 = emitter). However, the 2N5308's higher gain may require base resistor adjustment to avoid overdrive. Always revalidate thermal performance and switching speed in the target circuit before substituting the 2N5308.

What is the junction-to-ambient thermal resistance (RθJA) of the 2N5308?

The 2N5308 has a junction-to-ambient thermal resistance (RθJA) of 200°C/W under standard PCB mounting conditions (single-layer board, no copper pour). This value determines how much the junction temperature rises above ambient per milliwatt of dissipated power. For example, at 500 mW dissipation, TJ rises by 100°C above TA. To stay within the 150°C max junction limit, ambient temperature must be kept ≤50°C with no additional heatsinking-confirming the 2N5308's suitability for moderate-duty industrial use.