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

STMicroelectronics TIP121

Name: TIP121
Brand: STMicroelectronics
SKU: TIP121
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: TIP121

Manufacturer:: STMicroelectronics

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: TIP121.pdf

Description:: TRANS NPN DARL 80V 5A TO-220

Quantity:: RFQ Add To RFQ list

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Inventory:1,955

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Product details

Overview

TIP121 from STMicroelectronics is an NPN complementary power Darlington transistor in TO-220 package, rated for 80 V V_CEO, 5 A continuous collector current, and 65 W total power dissipation at T_C ≤ 25°C. It features monolithic Darlington configuration with integrated base resistors (R1 = 7 kΩ, R2 = 70 Ω), enabling direct TTL/CMOS drive in high-current linear and switching applications such as motor control and relay drivers.

For engineers reviewing the TIP121 datasheet, TIP121 pinout, TIP121 application, or TIP121 equivalent, key selection criteria include its low V_CE(sat) of 2 V at I_C = 3 A / I_B = 12 mA, DC current gain ≥1000 at I_C = 0.5 A, and junction-to-case thermal resistance of 1.92 °C/W - critical for thermal management in industrial power stages.

Technical Context

The TIP121 implements a planar "base island" layout with monolithic Darlington pairing, delivering high h_FE and low saturation voltage without external bias components. Its integrated R1/R2 network provides self-biasing, eliminating need for discrete base resistors in driver circuits.

Designed for operation up to 150°C junction temperature, it supports pulsed currents up to 8 A and exhibits stable gain across -40°C to 125°C ambient range. The device's safe operating area (SOA) is defined for both DC and pulsed conditions, with derating applied above 25°C case temperature.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO	80 V - maximum collector-emitter voltage before breakdown under open-base condition; defines upper rail limit in switching designs.
I_C (cont.)	5 A - continuous collector current rating at T_C ≤ 25°C; determines load-handling capability in motor or solenoid drivers.
V_CE(sat)	2 V @ I_C = 3 A, I_B = 12 mA - low saturation voltage minimizes conduction loss and heat generation in on-state operation.
h_FE	≥1000 @ I_C = 0.5 A, V_CE = 3 V - high DC current gain enables microcontroller GPIOs to directly drive high-current loads.
R_thJC	1.92 °C/W - junction-to-case thermal resistance; allows accurate heatsink sizing when mounted with thermal interface material.
P_TOT	65 W @ T_C ≤ 25°C - total power dissipation limit; sets maximum allowable I²R + V_CEI_C loss under ideal heatsinking.

Pinout & Package

Package: TO-220 type H (3-lead, vertical mounting, metal tab connected to collector). Tab is electrically connected to pin 2 (collector) and serves as primary thermal path.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Input control terminal	Accepts TTL/CMOS-compatible logic-level current; internal R1/R2 network ensures proper Darlington biasing without external components.
2 (Collector / Tab)	Main current output node	Electrically tied to metal tab; must be isolated from chassis unless circuit design intentionally references collector to ground or heatsink.
3 (Emitter)	Current return path	Connected to system ground or load return; forms low-impedance emitter-follower output stage in linear applications.

Key Features

Feature	Design Value
Integrated base resistors	R1 = 7 kΩ, R2 = 70 Ω - eliminates external bias network, reducing BOM count and PCB space in driver circuits.
Low V_CE(sat)	2 V @ 3 A - reduces conduction losses by >40% vs. standard bipolar transistors, improving efficiency in PWM-driven loads.
High h_FE	≥1000 - enables single-stage amplification from µA-level MCU outputs to multi-amp loads, simplifying gate/driver design.
Junction temperature limit	150°C - supports operation in enclosed industrial enclosures with limited airflow when properly heatsinked.

Applications

DC Motor Control

Relay Driver Circuit

Use Scenario: Driving 24 V, 3 A brushed DC motors in automated valves and conveyor modules.

IC Role / Device Role / Timing Role: High-current NPN switch controlling motor direction and enable via PWM input at base.

Use Value: Integrated base resistors allow direct connection to 3.3 V or 5 V microcontroller outputs; low V_CE(sat) limits heat rise to <15°C/W under full load.

Use Scenario: Replacing mechanical relays in PLC output modules handling 12–48 V AC/DC loads up to 5 A.

IC Role / Device Role / Timing Role: Solid-state replacement for electromechanical relay, switched by industrial I/O controller.

Use Value: Eliminates contact wear and bounce; fast turn-on (<100 ns delay) enables precise timing-critical actuation sequences.

Lamp Dimming Module

Linear Regulator Pass Element

Use Scenario: Phase-angle dimming of incandescent lamps in building automation systems using triac-triggered control.

IC Role / Device Role / Timing Role: Current amplifier stage driving triac gate with high di/dt capability.

Use Value: High h_FE ensures reliable triac triggering even with weak optocoupler outputs; SOA supports repetitive surge currents.

Use Scenario: Pass transistor in adjustable 0–30 V, 3 A linear power supply for test equipment calibration.

IC Role / Device Role / Timing Role: Series pass element controlled by error amplifier feedback loop.

Use Value: Low V_CE(sat) and high thermal conductivity (R_thJC = 1.92 °C/W) reduce dropout voltage and simplify heatsink requirements.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
TIP122	V_CEO = 100 V, same package and pinout	Higher voltage margin for 48 V bus systems; identical thermal and gain specs	Select when operating above 80 V rail or requiring additional safety margin against transients.
MJD127G	TO-263 surface-mount, V_CEO = 80 V, h_FE = 1000–5000, R_thJC = 2.5 °C/W	SMT-compatible; lower thermal performance but suitable for compact PCB layouts	Choose for automated assembly or space-constrained designs where thermal budget permits higher R_thJC.

Compared with TIP122 and MJD127G, the TIP121 offers optimal balance of voltage rating, thermal performance, and through-hole manufacturability for industrial 24–48 V power switching - making it preferred for field-serviceable or high-reliability wired assemblies.

Availability

TIP121 is available at Aetrix Electronics and suitable for DC motor control, relay driver circuits, lamp dimming modules, and linear regulator pass elements requiring stable component supply and long-term industrial availability.

Supply support for TIP121 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, specializing in power management, analog, microcontrollers, and automotive ICs.

The TIP121 belongs to the STPOWER™ Darlington family, engineered for robust high-current switching in industrial controls, factory automation, and power conversion where reliability and thermal resilience are critical.

FAQ

What is the maximum safe continuous collector current for TIP121?

The TIP121 is rated for 5 A continuous collector current at case temperature ≤25°C. At higher case temperatures, current must be derated per the datasheet curve - e.g., ~3.5 A at T_C = 70°C. Exceeding this without adequate heatsinking risks thermal runaway due to positive temperature coefficient of V_CE(sat).

Can TIP121 be driven directly from a 3.3 V microcontroller GPIO?

Yes - its integrated 7 kΩ base resistor allows direct connection to 3.3 V or 5 V logic outputs. With typical I_B ≈ 0.47 mA at 3.3 V, it delivers sufficient drive for I_C up to ~2 A (h_FE ≥1000). For full 5 A operation, a 5 V source or buffered drive is recommended to ensure I_B ≥20 mA.

Is the metal tab electrically isolated from the PCB mounting surface?

No - the TO-220 tab is internally connected to pin 2 (collector) and is not insulated. When mounting to a heatsink or chassis, electrical isolation via mica washer or silicone pad is required unless the collector node is intentionally referenced to that potential. Failure to isolate may cause short circuits or ground loops.

How does TIP121 compare to standard bipolar transistors like 2N3055 in switching applications?

The TIP121 provides ≥10× higher h_FE than 2N3055 (1000 vs. ~20–100), enabling direct logic-level drive without pre-driver stages. Its Darlington structure also yields lower V_CE(sat) at high currents (2 V vs. ~3–4 V), reducing conduction loss and thermal stress. However, it has slower turn-off due to stored charge, requiring careful snubber design in high-frequency switching.

TIP121 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):: 5 A

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

Vce Saturation (Max) @ Ib, Ic:: 4V @ 20mA, 5A

Current - Collector Cutoff (Max):: 500µA

DC Current Gain (hFE) (Min) @ Ic, Vce:: 1000 @ 3A, 3V

Power - Max:: 2 W

Frequency - Transition:: -

Operating Temperature:: 150°C (TJ)

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: TO-220

TIP121 FAQ

1.How can I place an order for TIP121 through Aetrix?

Please submit a Request for Quotation (RFQ) for TIP121 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 TIP121 reliable?

The price and inventory of TIP121 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for TIP121 is usually 5 days.

3.What payment methods are accepted for TIP121?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for TIP121 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for TIP121?

TIP121 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your TIP121 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 TIP121?

For technical support, including TIP121 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your TIP121 requirements.

6.How does Aetrix verify that TIP121 is sourced from the original manufacturer or authorized distributors?

All TIP121 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 TIP121 meets industry standards.

7.What is the process for return or replacement of TIP121?

All TIP121 units undergo pre-shipment inspection (PSI). If there is an issue with TIP121, 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 TIP121 part is unused and in its original packaging.

Return procedure for TIP121:

1.Submit a request within 90 days.

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

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