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The MJE3055T is a widely used NPN silicon power transistor known for its strength, reliability, and versatility across many power electronic applications. This article will discuss MJE3055T technical specifications, practical working examples, advantages, limitations, and more.
The MJE3055T is a robust NPN silicon power transistor designed for medium-power switching and amplification. Featuring a TO-220 package, it delivers up to 10 A of collector current and supports voltages up to 60 V, making it ideal for motor drivers, power regulators, and general-purpose power stages. Its epitaxial-base structure provides stable gain (typically hFE ≥ 20 at high currents) and reliable thermal performance when properly heatsinked, allowing it to operate effectively in demanding environments.
Engineered by STMicroelectronics, the MJE3055T offers a balance of durability and versatility, with a 75 W power dissipation rating, 2 MHz transition frequency, and a complementary PNP pair (MJE2955T ) for push-pull designs.
If you are interested in purchasing the MJE3055T, feel free to contact us for pricing and availability.
| Pin Number | Pin Name | Description |
| 1 | Base (B) | Controls the transistor’s operation; receives the input signal to turn the device on or off. |
| 2 | Collector (C) | Main current-carrying terminal; connects to the load in most switching applications. |
| 3 | Emitter (E) | Current exits through this terminal; typically connected to ground in NPN configurations. |
| Equivalent Part | Type | Package | Compatibility |
| TIP3055 | NPN Power Transistor | TO-218 / TO-247 | Best and closest equivalent; very similar electrical specs. |
| 2N3055 | NPN Power Transistor | TO-3 | Electrically similar; higher current, but different package (not drop-in). |
| MJE15015 | NPN Power Transistor | TO-247 | Higher voltage rating; good replacement in power circuits. |
| BD249C | NPN Power Transistor | TO-3P | Higher power handling; suitable as an upgraded substitute. |
| TIP35C | NPN Power Transistor | TO-247 | Higher current capability; works in many MJE3055T applications. |
| Parameter | Value |
| Manufacturer | STMicroelectronics |
| Transistor Type | NPN Power Transistor |
| Polarity | NPN |
| Part Status | Active |
| Package / Case | TO-220 / TO-220-3 |
| Mounting Type | Through Hole |
| Collector-Emitter Voltage (VCEO) | 60 V |
| Collector-Base Voltage (VCBO) | 70 V |
| Emitter-Base Voltage (VEBO) | 5 V |
| Collector Current (IC max) | 10 A |
| Collector Cutoff Current (ICBO) | 700 µA |
| DC Current Gain (hFE) @ 4 A, 4 V | 20 (min) |
| VCE Saturation @ 3.3 A / 10 A | 8 V max |
| Power Dissipation (Ptot) | 75 W |
| Transition Frequency (fT) | 2 MHz |
| Thermal Resistance (Junction–Case) | ~1.67 °C/W |
| Thermal Resistance (Junction–Ambient) | ~62.5 °C/W |
| Operating Junction Temperature (Tj) | 150°C |
| Storage Temperature Range | –65°C to +150°C |
| Pin Configuration | Pin 1 = Base, Pin 2 = Collector, Pin 3 = Emitter |
-NPN silicon power transistor in TO-220 package
-Designed for power switching and general-purpose amplifiers
-Complementary to PNP type MJE2955T
-High collector current up to 10 A
-High power dissipation up to 75 W (with proper heatsink)
-60 V collector-emitter voltage rating
-Moderate transition frequency (fT ≈ 2 MHz)
-Rugged construction and good thermal performance
In the audio amplifier circuit, the MJE3055T works as the main power transistor responsible for driving the lower half of the output waveform. It forms a complementary pair with the PNP transistor MJE2955, together creating a push–pull stage that delivers power to the speaker. When the input signal swings negative, the MJE3055T conducts and supplies current from the −35 V rail to the load. The smaller driver transistors (BD139/BD140) feed the necessary base current to the MJE3055T, allowing it to handle high output power while maintaining linear operation. Its emitter resistor helps stabilize the current and reduce distortion, ensuring clean audio reproduction.
In the second circuit, the MJE3055T acts as a series pass transistor in a simple voltage regulator. A 5.6 V Zener diode provides a stable reference at the base, and because the emitter follows this voltage minus about 0.6 V, the output becomes a regulated supply of roughly 5 V. The resistor feeds current into the Zener diode to keep it in regulation, while the capacitors smooth the voltage and reduce ripple. Here, the MJE3055T increases the current-handling capability of the regulator, allowing the circuit to deliver a stable, low-noise supply to whatever load is connected.
-Audio power amplifiers (output stage or driver stage)
-DC power supply regulators (series pass transistor)
-Motor drivers and small DC motor control
-Relay and solenoid switching for medium-to-high current loads
-Inverters and power conversion circuits
-Battery chargers and power distribution modules
-LED driving for high-current lighting systems
-General-purpose high-current switching in hobby and industrial electronics
| Specification | MJE3055T | MJE3055TG |
| Type | NPN Power Transistor | NPN Power Transistor |
| Package | TO-220 | TO-220 |
| Lead Finish | Standard (may include older leaded versions) | Pb-free / RoHS-compliant (TG suffix) |
| Collector-Emitter Voltage (VCEO) | 60 V | 60 V |
| Collector-Base Voltage (VCBO) | 70 V | 70 V |
| Emitter-Base Voltage (VEBO) | 5 V | 5 V |
| Continuous Collector Current (IC) | 10 A | 10 A |
| Power Dissipation (Ptot) | 75 W | 75 W |
| DC Current Gain (hFE) | 20 (min at 4 A) | 20 (min at 4 A) |
| Transition Frequency (fT) | ~2 MHz | ~2 MHz |
| Thermal Resistance (Junction-Case) | Same typical value | Same typical value |
| Safe Operating Area | Same curve profile | Same curve profile |
| Main Difference | Standard version | Environmentally-compliant version (Pb-free/halogen-free) |
-Handles relatively high current (up to 10 A) suitable for power applications
-High power dissipation capability (around 75 W with proper heatsinking)
-Widely available and cost-effective
-Easy to mount due to TO-220 package
-Suitable for audio amplifiers, motor drivers, and power regulators
-Good reliability for linear and switching applications
-Compatible with many standard circuit designs
-Works well as a series pass transistor in regulated power supplies
-Maximum voltage rating is moderate (60 V), not suitable for high-voltage circuits
-Requires proper heatsinking or it can overheat quickly
-Slower switching speed compared to modern power transistors
-Limited gain (hFE), often needing a driver stage
-Not ideal for high-frequency switching power supplies
-Junction temperature limits performance under heavy loads
-Older transistor design compared to newer MOSFET alternatives
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