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

STMicroelectronics ST901T

Name: ST901T
Brand: STMicroelectronics
SKU: ST901T
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: ST901T

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: ST901T.pdf

Description:: TRANS NPN DARL 350V 4A TO-220

Quantity:: RFQ Add To RFQ list

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Inventory:1,986

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Product details

Overview

ST901T from STMicroelectronics is a high-voltage NPN Darlington transistor in TO-220 package, designed for electronic ignition in small internal combustion engines. It delivers 500 V V_CES, 4 A continuous collector current, and DC current gain of 1800–3800 at 2 A, enabling robust coil driver operation in scooters, lawnmowers, and chainsaws.

For engineers reviewing the ST901T datasheet, ST901T pinout, ST901T application, or ST901T equivalent, key selection criteria include V_CEO(sus) = 350 V, t_s = 15 μs storage time, R_thJC = 1.25 °C/W, and rugged bipolar Darlington structure optimized for high-energy ignition pulse handling.

Technical Context

The ST901T implements a monolithic high-voltage Darlington configuration with integrated base-emitter shunt resistor network to ensure reliable turn-off under inductive load conditions. Its 350 V V_CEO(sus) rating and 2 V V_CE(sat) at 2 A/20 mA support fast, low-loss switching in ignition coil primary drive circuits.

Thermal performance is defined by R_thJC = 1.25 °C/W and T_J range from –65 °C to +150 °C, enabling operation in harsh ambient environments typical of outdoor power equipment. The device uses rugged bipolar technology-not MOSFET or IGBT-optimized for high dV/dt immunity and avalanche energy tolerance.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CES	500 V - Withstands full coil flyback voltage without breakdown during open-circuit ignition events
V_CEO(sus)	350 V - Sustains rated collector-emitter voltage under pulsed 10 mA test condition, critical for clamp-limited ignition cycles
I_C	4 A - Continuous collector current capability sufficient for driving 4–6 mH ignition coils at 12–24 V supply
h_FE	1800–3800 @ 2 A - High DC gain reduces required base drive current, easing microcontroller GPIO or driver IC interface
t_s	15 μs - Storage time directly impacts minimum spark repetition rate and maximum engine RPM support
R_thJC	1.25 °C/W - Enables 100 W dissipation at T_C = 25 °C, supporting high-duty-cycle ignition in air-cooled applications

Pinout & Package

ST901T is housed in a TO-220 type A package with insulated tab (electrically connected to collector). The case serves as thermal path and mechanical mounting surface.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Control input	Receives base current to initiate conduction; requires ≥20 mA for full saturation at 2 A I_C
2 (Collector / TAB)	Main power output	Connected internally to metal tab; must be electrically isolated from heatsink unless circuit design permits common-collector reference
3 (Emitter)	Power return path	Serves as low-side switch emitter; referenced to ground in standard ignition coil driver topology

Key Features

Feature	Design Value
High-voltage Darlington structure	Monolithic integration eliminates external base resistor dependency and improves thermal coupling between stages
Rugged bipolar technology	Withstands repetitive 350 V sustaining voltage and 500 V peak collector-emitter stress without degradation
High DC current gain	h_FE ≥1800 at 2 A enables direct drive from low-current MCU outputs or logic-level gate drivers
Fast storage time	t_s = 15 μs supports spark frequencies up to ~30 kHz, covering full RPM range of small engines up to 18,000 RPM

Applications

Small Engine Ignition

Capacitive Discharge Ignition (CDI)

Use Scenario: Electronic spark timing control in 50 cc scooter engines operating at 0–12,000 RPM.

IC Role / Device Role / Timing Role: Low-side switch for primary winding of ignition coil; triggered by microcontroller PWM or dedicated ignition controller.

Use Value: 350 V V_CEO(sus) ensures reliable operation during capacitor discharge transients; 15 μs t_s enables precise spark timing at high RPM.

Use Scenario: Primary-side switching in solid-state CDI modules for handheld power tools.

IC Role / Device Role / Timing Role: High-speed, high-voltage switch controlling energy transfer from storage capacitor to ignition coil.

Use Value: 500 V V_CES withstands capacitor recharge overshoot; 2 V V_CE(sat) minimizes conduction loss during short on-pulse durations.

Lawnmower Ignition Module

Chainsaw Electronic Ignition

Use Scenario: Replacement for mechanical breaker points in walk-behind rotary lawnmowers.

IC Role / Device Role / Timing Role: Solid-state replacement for contact-based switching; driven by flywheel-mounted magnet sensor signal.

Use Value: 100 μA I_CEO ensures minimal leakage current during dwell period; –65 °C to +150 °C T_J range covers outdoor temperature extremes.

Use Scenario: Compact ignition driver in battery-powered or recoil-start chainsaws with integrated timing control.

IC Role / Device Role / Timing Role: High-reliability switch interfacing with Hall-effect or variable reluctance crank position sensors.

Use Value: R_thJC = 1.25 °C/W allows direct mounting to aluminum housing for passive cooling; TO-220 mechanical robustness resists vibration-induced failure.

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-voltage Darlington ignition switch applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
BU508AF	V_CEO = 700 V, h_FE = 10–40 (lower gain), TO-220FP package with non-insulated tab	Higher voltage margin but requires external base resistor and higher drive current; less suitable for direct MCU drive	Prefer when >500 V flyback margin is mandatory and board space allows discrete base bias network
TIP122	V_CEO = 100 V, h_FE = 1000 min, TO-220 package with insulated tab	Insufficient V_CEO for ignition coil flyback; limited to low-voltage (<120 V) inductive loads	Only acceptable in pre-regulated 12 V systems with active clamping; not drop-in for ST901T ignition use cases

Compared with BU508AF and TIP122, ST901T uniquely combines 350 V sustaining voltage, 1800+ h_FE, and insulated TO-220 packaging-enabling compact, low-component-count ignition designs without external base biasing or clamping.

Availability

ST901T is available at Aetrix Electronics and suitable for small engine ignition systems, capacitive discharge ignition modules, and lawnmower/chainsaw electronic control units requiring stable component supply and long-term industrial availability.

Supply support for ST901T 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, Switzerland, designing and manufacturing analog, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

ST901T belongs to ST's high-voltage power transistor product line, engineered specifically for rugged, high-energy switching in ignition, ballast, and industrial solenoid control applications.

FAQ

What is the maximum safe operating junction temperature for ST901T?

The ST901T has a specified junction temperature range of –65 °C to +150 °C. Operation above +150 °C risks permanent parametric shift or thermal runaway. Derating is required above T_C = 25 °C per R_thJC = 1.25 °C/W; full 100 W dissipation is only valid at case temperature ≤25 °C.

Can ST901T replace TIP122 in an existing ignition circuit?

No-TIP122 has only 100 V V_CEO, while ST901T is rated for 350 V sustaining voltage. Substituting ST901T into a TIP122 design may cause overvoltage failure if flyback clamping is inadequate. Conversely, replacing ST901T with TIP122 will result in immediate breakdown during normal ignition coil flyback.

Is the TO-220 tab electrically isolated on ST901T?

Yes-the TO-220 package used for ST901T is type A with insulated tab. The metal tab is internally connected to the collector but electrically isolated from the mounting surface by a dielectric coating, allowing direct heatsink mounting without additional insulator washers.

What is the recommended base drive for reliable saturation at 4 A collector current?

Per datasheet Figure 3 and Table 3, h_FE drops to ≥500 at I_C = 4 A. To ensure saturation, apply ≥8 mA base current (4 A ÷ 500). For safety margin and temperature stability, 20 mA base drive is recommended-achievable via 220 Ω resistor from 5 V MCU output or dedicated driver stage.

ST901T Specifications

Product attributes: Attribute value

Manufacturer:: STMicroelectronics

Series:: -

Package/Case:: TO-220-3

Packaging:: Tube

Product Status:: Active

Transistor Type:: NPN - Darlington

Current - Collector (Ic) (Max):: 4 A

Voltage - Collector Emitter Breakdown (Max):: 350 V

Vce Saturation (Max) @ Ib, Ic:: 2V @ 20mA, 2A

Current - Collector Cutoff (Max):: 100µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 1800 @ 2A, 2V

Power - Max:: 100 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

ST901T FAQ

1.How can I place an order for ST901T through Aetrix?

Please submit a Request for Quotation (RFQ) for ST901T 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 ST901T reliable?

The price and inventory of ST901T are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for ST901T is usually 5 days.

3.What payment methods are accepted for ST901T?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for ST901T transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for ST901T?

ST901T orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your ST901T 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 ST901T?

For technical support, including ST901T datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your ST901T requirements.

6.How does Aetrix verify that ST901T is sourced from the original manufacturer or authorized distributors?

All ST901T 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 ST901T meets industry standards.

7.What is the process for return or replacement of ST901T?

All ST901T units undergo pre-shipment inspection (PSI). If there is an issue with ST901T, 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 ST901T part is unused and in its original packaging.

Return procedure for ST901T:

1.Submit a request within 90 days.

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

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