onsemi MJD122T4

Overview

MJD122T4 from onsemi is an NPN complementary Darlington power transistor in DPAK surface-mount package, rated for 8 A continuous collector current, 100 V collector-emitter voltage, and 20 W power dissipation at T_C = 25 °C. It features monolithic construction with built-in base-emitter shunt resistors, typical DC current gain (h_FE) of 2500 at I_C = 4 A, and AEC-Q101 qualification for automotive applications such as motor driver stages and relay drivers.

For engineers reviewing the MJD122T4 datasheet, pinout, applications, or equivalent options, this device serves as a surface-mount replacement for legacy through-hole Darlington transistors including the TIP120–TIP122 series and 2N6040–2N6045 family - with verified thermal performance, Pb-free RoHS compliance, and validated switching behavior under low-speed switching and linear amplifier conditions.

Technical Context

The MJD122T4 implements a monolithic NPN Darlington pair with integrated base-emitter shunt resistors to ensure reliable turn-off and reduce external component count. Its architecture supports high-current, low-frequency amplification and switching, with guaranteed V_CE(sat) ≤ 2 V at I_C = 4 A / I_B = 16 mA and V_BE(sat) ≤ 4.5 V at I_C = 8 A / I_B = 80 mA.

Thermal design is enabled by a low junction-to-case thermal resistance of 6.25 °C/W and defined derating curves for both case- and ambient-mounted configurations. The device operates across −65 °C to +150 °C junction temperature range and meets UL 94 V-0 flammability rating at 0.125 in thickness.

Key Specifications

Pinout & Package

DPAK-3 (Case 369C, Style 1) surface-mount package with exposed collector tab (pins 2 and 4 electrically common), 6.10 mm × 6.54 mm footprint, and 2.28 mm height. Thermal pad on underside requires soldered copper area for optimal R_θJA performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BD679A, MJD122T4 delivers higher current, higher voltage, and automotive qualification in the same DPAK footprint; compared with MJD122G, it offers identical performance with optimized logistics for high-volume SMT production via 2500-unit tape-and-reel delivery.

Availability

MJD122T4 is available at Aetrix Electronics and suitable for automotive seat control, industrial relay replacement, DC fan speed regulation, and linear regulator pass-element applications requiring stable component supply, long-term lifecycle support, and AEC-Q101-compliant sourcing.

Supply support for MJD122T4 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier focused on energy-efficient electronics, delivering silicon solutions for automotive, industrial, cloud, and IoT markets.

The MJD122T4 belongs to onsemi's complementary Darlington power transistor product line, engineered for robust, high-current switching and amplification in harsh environments - especially where reliability, thermal resilience, and automotive-grade validation are mandatory.

FAQ

What is the maximum continuous collector current rating for the MJD122T4?

The MJD122T4 is rated for 8 A continuous collector current (I_C) at case temperature T_C = 25 °C. This rating assumes proper PCB copper area per the DPAK thermal pad layout guidelines in the datasheet. Derating applies above 25 °C at 0.16 W/°C, and actual usable current depends on heatsinking and ambient conditions. The MJD122T4 maintains safe operation up to its second-breakdown limit, validated in Figure 12 of the official onsemi datasheet.

Is the MJD122T4 pin-compatible with the TIP122?

No - the MJD122T4 uses a DPAK-3 surface-mount package (pins: 1=Base, 2&4=Collector, 3=Emiter), whereas the TIP122 uses TO-220 through-hole packaging (pins: 1=Base, 2=Collector, 3=Emiter). Though functionally similar as NPN Darlington transistors, their footprints, thermal paths, and mechanical mounting differ fundamentally. The MJD122T4 replaces the TIP122 in new SMT designs but requires PCB layout revision, not drop-in substitution.

Does the MJD122T4 include internal base-emitter resistors?

Yes - the MJD122T4 features monolithic construction with built-in base-emitter shunt resistors, as confirmed in the "Features" section of the onsemi datasheet. These resistors ensure reliable turn-off by preventing charge accumulation at the base node, eliminating the need for external pull-down resistors in most switching applications and improving noise immunity in automotive and industrial settings.

What is the thermal resistance junction-to-case (R_θJC) for the MJD122T4?

The MJD122T4 has a specified thermal resistance of R_θJC = 6.25 °C/W, measured from junction to the collector tab (pins 2 and 4). This value assumes proper soldering of the exposed thermal pad to a minimum copper area as defined in the DPAK footprint recommendations. It enables accurate junction temperature estimation using T_J = T_C + (P_D × R_θJC), critical for reliability validation in high-power linear or switching operation of the MJD122T4.

Is the MJD122T4 suitable for PWM motor control applications?

Yes - the MJD122T4 is designed for low-speed switching and general-purpose amplifier applications, with verified switching times (t_d, t_r, t_s, t_f) documented in Figure 10 of the datasheet. While not optimized for high-frequency PWM (>20 kHz), it performs reliably in 1–5 kHz motor control loops for DC brushed motors, fans, and solenoids. Its V_CE(sat) ≤ 2 V and h_FE ≥ 1000 simplify gate/base drive design, making the MJD122T4 well-suited for cost-sensitive, thermally constrained PWM implementations.