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Home > Products > Discrete Semiconductor Products > Transistors > Bipolar (BJT) > Single Bipolar Transistors

STMicroelectronics MJE172

Name: MJE172
Brand: STMicroelectronics
SKU: MJE172
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: MJE172

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-225AA, TO-126-3

Datasheet:: MJE172.pdf

Description:: TRANS PNP 80V 3A SOT-32-3

Quantity:: RFQ Add To RFQ list

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Inventory:3,159

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Product details

Overview

MJE172 from STMicroelectronics is an NPN low-voltage, high-speed switching transistor in SOT-32 (TO-126) package, rated for V_CEO = 80 V, I_C = 3 A, and f_T = 50 MHz, with V_CE(sat) = 0.3 V at I_C = 0.5 A / I_B = 50 mA - used in low-power audio amplifiers and pulse-width modulation switch stages.

For engineers reviewing the MJE172 datasheet, MJE172 pinout, MJE172 application, or MJE172 equivalent, key selection considerations include its 12.5 W total dissipation at T_c ≤ 25 °C, R_thJC = 10 °C/W thermal resistance, and suitability for linear amplification and saturated switching below 100 kHz.

Technical Context

The MJE172 is a silicon epitaxial-planar NPN transistor optimized for low-voltage (<80 V), medium-current (≤3 A) operation with fast turn-on/turn-off characteristics. Its h_FE ranges from 12 to 250 across I_C = 0.1–1.5 A, supporting both linear gain control and hard saturation switching.

Designed for thermal reliability in through-hole PCB mounting, it features a TO-126-compatible SOT-32 package with metal tab for heatsinking, and exhibits C_CBO = 60 pF at V_CB = 10 V, enabling stable performance in audio-frequency and low-MHz switching circuits.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	80 V - maximum collector-emitter voltage before breakdown under open-base condition; defines safe operating voltage ceiling in switching applications
I_C	3 A - continuous DC collector current rating; supports medium-power driver and amplifier stages
f_T	50 MHz - transition frequency at I_C = 0.1 A, V_CE = 10 V; enables reliable operation up to ~5–10 MHz small-signal amplification
V_CE(sat)	0.3 V @ I_C = 0.5 A / I_B = 50 mA - low saturation voltage minimizes conduction loss in switching regulators and logic-level drivers
R_thJC	10 °C/W - junction-to-case thermal resistance; allows direct heatsink mounting for sustained 12.5 W dissipation at case temperature ≤25 °C
h_FE	50–250 - DC current gain range across I_C = 0.1–0.5 A; supports bias stability in Class-A audio preamps and base-driven switches

Pinout & Package

The MJE172 is housed in a SOT-32 package - identical in outline and mounting to TO-126 - with emitter (E), base (B), and collector (C) leads arranged in linear order; collector connected internally to the metal tab for thermal and electrical grounding.

Pin/Terminal	Circuit Role	Design Meaning
Emitter (E)	Current sink terminal	Low-impedance return path; typically grounded or tied to negative rail in common-emitter configurations
Base (B)	Control input	Receives forward-biased drive current (≤1 A peak); requires series resistor to limit I_B per h_FE target
Collector (C)	Current source terminal	Connected to load and supply; metal tab is electrically tied to collector for heatsinking and simplified layout

Key Features

Feature	Design Value
High-speed switching capability	50 MHz f_T and low C_CBO (60 pF) enable clean edge response in PWM and pulse generator circuits up to 10 MHz
Low V_CE(sat)	0.3 V at moderate drive ensures <150 mW conduction loss at 0.5 A, improving efficiency in battery-powered switches
SOT-32 (TO-126) package	Through-hole metal-tab package supports >12 W power dissipation with minimal PCB area and direct heatsink interface
Wide h_FE range	12–250 gain spread accommodates production variance while maintaining functional margin in amplifier bias networks

Applications

Audio Amplifier Stage

DC Motor Driver

Use Scenario: Low-voltage Class-A preamplifier stage in portable audio equipment with ±12 V rails.

IC Role / Device Role / Timing Role: NPN transconductance amplifier providing voltage gain and impedance buffering between op-amp output and speaker load.

Use Value: h_FE ≥50 at I_C = 0.1 A ensures stable quiescent bias; low V_CE(sat) prevents clipping near rail limits.

Use Scenario: Single-ended H-bridge half-bridge switch controlling 24 V, 1.5 A brushed DC motor in industrial actuators.

IC Role / Device Role / Timing Role: Saturated NPN switch turning motor winding on/off via microcontroller GPIO with base resistor network.

Use Value: I_C = 3 A rating and 6 A peak current support handle motor stall surges; R_thJC = 10 °C/W enables passive heatsinking.

LED Constant-Current Driver

Pulse Generator Output Stage

Use Scenario: Linear constant-current sink for high-brightness LED strings in signage systems operating from 5–24 V supplies.

IC Role / Device Role / Timing Role: Emitter-follower configured transistor regulating LED current via feedback resistor and reference voltage.

Use Value: V_CEO = 80 V headroom accommodates transient spikes; low V_BE(sat) = 1.5 V minimizes dropout across sense resistor.

Use Scenario: Final-stage pulse shaper in function generator delivering 0–5 V, 100 ns rise-time square waves into 50 Ω loads.

IC Role / Device Role / Timing Role: Common-emitter switch biased for fast edge transitions, driven by TTL/CMOS logic with active base pull-down.

Use Value: f_T = 50 MHz and C_CBO = 60 pF ensure <15 ns propagation delay and minimal overshoot at 5 MHz repetition rates.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
2N3055	Higher V_CEO (100 V), lower f_T (~0.8 MHz), TO-3 metal package	Better for high-voltage linear regulation; unsuitable for >100 kHz switching due to slow recovery	Choose when >60 V operation or >15 A surge handling is required; avoid for high-frequency PWM
BC548	Lower I_C (0.1 A), smaller SOT-23 package, f_T = 300 MHz	Optimized for signal amplification and logic interfacing, not power switching	Use only for sub-100 mA loads; insufficient for motor or audio output stages requiring >500 mA

Compared with 2N3055 and BC548, the MJE172 uniquely balances medium current (3 A), medium voltage (80 V), and RF-grade speed (50 MHz) in a thermally robust through-hole package - making it optimal for cost-sensitive, board-mounted switching where TO-3 is oversized and SOT-23 lacks power handling.

Availability

MJE172 is available at Aetrix Electronics and suitable for audio amplifier design, DC motor control, LED driver development, and pulse generator prototyping requiring stable component supply and legacy part continuity.

Supply support for MJE172 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing analog, digital, and mixed-signal ICs and discrete devices for industrial, automotive, and consumer markets.

The MJE172 belongs to ST's legacy bipolar power transistor family, developed specifically for cost-effective, thermally reliable linear and switching applications in industrial controls and audio systems.

FAQ

Is MJE172 RoHS-compliant and lead-free?

Yes, the MJE172 is manufactured in ST's ECOPACK®-compliant SOT-32 package, meeting RoHS Directive 2011/65/EU requirements. Lead-free soldering profiles are validated per J-STD-020, and the device carries the "ECOPACK2" marking per ST's environmental compliance documentation.

Can MJE172 be used in complementary pair configurations with PNP transistors?

Yes - the MJE172 is commonly paired with the PNP MJE182 (V_CEO = −80 V, I_C = −3 A) for push-pull audio output stages. Both share matched h_FE ranges, thermal characteristics, and SOT-32 packaging, enabling symmetrical drive and thermal tracking.

What is the maximum safe operating frequency for MJE172 in switching mode?

While f_T = 50 MHz indicates small-signal gain bandwidth, practical hard-switching operation is limited to ≤5 MHz due to stored charge and minority carrier lifetime. For 100 kHz–1 MHz PWM, it delivers reliable saturation with <100 ns turn-off delay when base is actively pulled low.

Does MJE172 require a heatsink in continuous 3 A operation?

Yes - at I_C = 3 A and V_CE = 1 V (3 W dissipation), ambient temperatures above 40 °C exceed safe junction limits without heatsinking. With R_thJC = 10 °C/W and R_thCA ≈ 83 °C/W, a 25 cm² aluminum heatsink reduces junction rise to <65 °C at 25 °C ambient.

MJE172 Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-225AA, TO-126-3

Packaging:: Tube

Product Status:: Obsolete

Transistor Type:: PNP

Current - Collector (Ic) (Max):: 3 A

Voltage - Collector Emitter Breakdown (Max):: 80 V

Vce Saturation (Max) @ Ib, Ic:: 1.7V @ 600mA, 3A

Current - Collector Cutoff (Max):: 100nA (ICBO)

DC Current Gain (hFE) (Min) @ Ic, Vce:: 50 @ 100mA, 1V

Power - Max:: 12.5 W

Frequency - Transition:: 50MHz

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: SOT-32-3

MJE172 FAQ

1.How can I place an order for MJE172 through Aetrix?

Please submit a Request for Quotation (RFQ) for MJE172 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for MJE172 reliable?

The price and inventory of MJE172 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for MJE172 is usually 5 days.

3.What payment methods are accepted for MJE172?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for MJE172 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for MJE172?

MJE172 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your MJE172 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for MJE172?

For technical support, including MJE172 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your MJE172 requirements.

6.How does Aetrix verify that MJE172 is sourced from the original manufacturer or authorized distributors?

All MJE172 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that MJE172 meets industry standards.

7.What is the process for return or replacement of MJE172?

All MJE172 units undergo pre-shipment inspection (PSI). If there is an issue with MJE172, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The MJE172 part is unused and in its original packaging.

Return procedure for MJE172:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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