Send an Inquiry

To receive a quote for your project, please fill in the following information, and we’ll get back to you promptly.

Submit Inventory List

Please fill in the following information, and we’ll get back to you promptly.

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

onsemi TIP121

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

Compare

Part No.:: TIP121

Manufacturer:: onsemi

Category:: Single Bipolar Transistors

Package:: TO-220-3

Datasheet:: TIP121.pdf

Description:: TRANS NPN DARL 80V 5A TO-220-3

Quantity:: RFQ Add To RFQ list

Payment:

Shipping:

Inventory:9,186

Please send an inquiry. Send us your inquiry, and we will respond immediately.

Product details

Overview

TIP121 from ON Semiconductor is an NPN epitaxial Darlington transistor designed for medium-power linear and switching applications, with 80 V collector-emitter sustaining voltage (V_CEO(sus)), 5 A DC collector current (I_C), and 65 W collector dissipation at T_C = 25°C; it serves as a high-gain power switch in motor drivers, relay interfaces, and lamp controls.

For engineers reviewing the TIP121 datasheet, pinout, applications, or equivalent options, key selection considerations include its 80 V V_CEO(sus), 1000 minimum h_FE at I_C = 0.5 A and 3 A, 2.0 V V_CE(sat) at I_C = 3 A / I_B = 12 mA, TO-220 package thermal performance, and complementary pairing with TIP126.

Technical Context

The TIP121 integrates two cascaded NPN transistors in a monolithic Darlington configuration with internal base-emitter resistors (R₁ ≈ 8 kΩ, R₂ ≈ 0.12 kΩ), enabling high DC current gain (h_FE ≥ 1000) and simplified drive requirements. It operates with a 5 V emitter-base voltage limit (V_EBO) and supports pulse currents up to 8 A (I_CP).

Its safe operating area (SOA) is defined for DC, 10 ms, 1 ms, and 100 μs conditions, and thermal derating begins at T_C > 25°C, with maximum junction temperature rated at 150°C and storage range from −65°C to +150°C.

Key Specifications

Parameter	Value and Actual Design Meaning
V_CEO(sus)	80 V - Sustaining voltage under switching conditions with I_C = 100 mA, defining maximum off-state collector-emitter blocking capability
I_C (DC)	5 A - Continuous collector current rating, determining steady-state load-handling capacity in linear or saturated operation
h_FE	≥1000 - Minimum DC current gain at both I_C = 0.5 A and I_C = 3 A, enabling low-base-drive design for high-current loads
V_CE(sat)	2.0 V @ I_C = 3 A / I_B = 12 mA - Saturation voltage defining conduction loss and heat generation in switch-mode use
P_C (T_C = 25°C)	65 W - Maximum power dissipation with case heatsink at 25°C, setting thermal design baseline for TO-220 mounting
C_ob	200 pF @ V_CB = 10 V - Output capacitance affecting switching speed and high-frequency response in PWM or AC-coupled circuits

Pinout & Package

Package: TO-220 3L (Single Gauge), through-hole, vertical mounting with metal tab electrically connected to collector; requires insulated mounting hardware when collector is not at chassis ground.

Pin/Terminal	Circuit Role	Design Meaning
1 (Base)	Control input terminal	Receives low-current drive signal; internal 8 kΩ resistor to first transistor base enables single-resistor biasing
2 (Collector)	High-current output node	Connected to metal tab; carries full load current and must be thermally coupled to heatsink
3 (Emitter)	Current return path	Common reference for load; internal 0.12 kΩ resistor between emitter and second transistor emitter improves turn-off behavior

Key Features

Feature	Design Value
Monolithic Darlington structure	Two NPN transistors integrated on one die with built-in base-emitter resistors, eliminating external bias components
High DC current gain	h_FE ≥ 1000 across 0.5–3 A collector current range, reducing required base drive current by >99% vs. single transistor
Internal emitter resistor	0.12 kΩ resistor between emitter terminals accelerates turn-off and improves switching consistency
TO-220 thermal performance	65 W power dissipation at T_C = 25°C enables direct heatsink mounting without auxiliary thermal interface layers in many 5 A applications

Applications

DC Motor Control	Relay Driver
Use Scenario: Driving 12–24 V brushed DC motors in industrial actuators or automotive accessories requiring 3–5 A continuous current. IC Role / Device Role / Timing Role: High-gain power switch controlling motor direction and enable via base signal; handles back-EMF during commutation. Use Value: 80 V V_CEO(sus) safely clamps inductive kickback; 2.0 V V_CE(sat) limits conduction loss to ≤6 W at 3 A, easing thermal management.	Use Scenario: Replacing mechanical switches in programmable logic controllers (PLCs) to energize 24 VDC relays with coil currents up to 4 A. IC Role / Device Role / Timing Role: Solid-state load switch interfacing microcontroller GPIO to relay coil; provides galvanic isolation from control side. Use Value: 1000 h_FE allows direct drive from 3.3 V/5 V MCU pins with only a series current-limiting resistor; TO-220 package supports repeated switching cycles.
Lamp Dimming Circuit	Power Supply Pass Element
Use Scenario: Phase-angle or PWM dimming of incandescent or halogen lamps (up to 500 W at 120 VAC) using zero-crossing triac driver stage. IC Role / Device Role / Timing Role: Current amplifier stage driving triac gate; handles peak surge currents during lamp cold-start. Use Value: 8 A pulse current rating (I_CP) accommodates inrush surges; 200 pF C_ob minimizes false triggering from dv/dt noise in AC line environments.	Use Scenario: Linear pass transistor in adjustable bench power supplies delivering 0–30 V / 0–3 A with analog voltage control. IC Role / Device Role / Timing Role: Regulating element dissipating excess voltage as heat; operated in active region with feedback loop compensation. Use Value: 65 W T_C-referenced dissipation supports stable 3 A output at 10 V drop (30 W); SOA curves validate safe operation under transient overload.

DC Motor Control

Relay Driver

Use Scenario: Driving 12–24 V brushed DC motors in industrial actuators or automotive accessories requiring 3–5 A continuous current.

IC Role / Device Role / Timing Role: High-gain power switch controlling motor direction and enable via base signal; handles back-EMF during commutation.

Use Value: 80 V V_CEO(sus) safely clamps inductive kickback; 2.0 V V_CE(sat) limits conduction loss to ≤6 W at 3 A, easing thermal management.

Use Scenario: Replacing mechanical switches in programmable logic controllers (PLCs) to energize 24 VDC relays with coil currents up to 4 A.

IC Role / Device Role / Timing Role: Solid-state load switch interfacing microcontroller GPIO to relay coil; provides galvanic isolation from control side.

Use Value: 1000 h_FE allows direct drive from 3.3 V/5 V MCU pins with only a series current-limiting resistor; TO-220 package supports repeated switching cycles.

Lamp Dimming Circuit

Power Supply Pass Element

Use Scenario: Phase-angle or PWM dimming of incandescent or halogen lamps (up to 500 W at 120 VAC) using zero-crossing triac driver stage.

IC Role / Device Role / Timing Role: Current amplifier stage driving triac gate; handles peak surge currents during lamp cold-start.

Use Value: 8 A pulse current rating (I_CP) accommodates inrush surges; 200 pF C_ob minimizes false triggering from dv/dt noise in AC line environments.

Use Scenario: Linear pass transistor in adjustable bench power supplies delivering 0–30 V / 0–3 A with analog voltage control.

IC Role / Device Role / Timing Role: Regulating element dissipating excess voltage as heat; operated in active region with feedback loop compensation.

Use Value: 65 W T_C-referenced dissipation supports stable 3 A output at 10 V drop (30 W); SOA curves validate safe operation under transient overload.

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	100 V V_CEO(sus), same I_C/h_FE/package; higher voltage rating increases margin in 48 V or rectified AC systems	Preferred where bus voltage exceeds 80 V, e.g., 48 V telecom power distribution or 100 VAC-derived supplies	Select TIP122 when V_CE stress approaches 70 V in worst-case transients; otherwise TIP121 offers optimal cost/performance balance at ≤80 V
MJD127G	TO-263 surface-mount package; 80 V V_CEO, 5 A I_C, but h_FE min = 750 (lower gain), no internal emitter resistor	Suitable for automated PCB assembly; requires external turn-off assist circuitry for fast switching	Choose MJD127G only for space-constrained SMT designs accepting reduced gain and added layout complexity; TIP121 remains preferred for through-hole reliability and ease of prototyping

Compared with TIP122 and MJD127G, the TIP121 delivers the best combination of 80 V blocking, 1000 h_FE, internal turn-off resistor, and TO-220 thermal robustness for general-purpose medium-power switching-making it the default choice unless higher voltage or SMT is mandatory.

Availability

TIP121 is available at Aetrix Electronics and suitable for DC motor control, relay driving, lamp dimming, and linear power supply applications requiring stable component supply, long-term obsolescence planning, and traceable sourcing.

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

ON Semiconductor is a global semiconductor manufacturer specializing in power management, analog, sensor, and discrete devices for automotive, industrial, and cloud power applications.

The TIP121 belongs to the TIP12x family of high-gain Darlington transistors engineered for robust medium-power switching in cost-sensitive industrial controls and legacy equipment replacement.

FAQ

What is the maximum collector-emitter sustaining voltage for the TIP121?

The TIP121 has a collector-emitter sustaining voltage (V_CEO(sus)) of 80 V under test conditions of I_C = 100 mA and I_B = 0. This rating defines its safe off-state blocking capability in switching applications and must be derated per SOA curves during transient events. The TIP121 datasheet confirms this value on page 2 under Electrical Characteristics.

Does the TIP121 have built-in base-emitter resistors?

Yes, the TIP121 integrates two internal resistors: R₁ ≈ 8 kΩ between base and the first transistor's base, and R₂ ≈ 0.12 kΩ between emitter terminals. These eliminate need for external bias resistors and improve turn-off behavior. The equivalent circuit diagram on page 2 of the TIP121 datasheet explicitly shows these components.

What is the saturation voltage of the TIP121 at 3 A collector current?

The TIP121 exhibits a collector-emitter saturation voltage (V_CE(sat)) of 2.0 V when operated at I_C = 3 A and I_B = 12 mA, as specified in the Electrical Characteristics table on page 2 of the official datasheet. This value determines conduction loss and corresponding thermal load in switched-mode operation.

Can the TIP121 replace the TIP120 in an existing design?

Yes, the TIP121 can directly replace the TIP120 in most designs because both share identical pinout, package (TO-220), gain (h_FE ≥ 1000), and saturation characteristics-but the TIP121 offers higher 80 V V_CEO(sus) versus 60 V for the TIP120. Review SOA and thermal margins if operating near 60 V to ensure headroom remains sufficient.

What is the maximum power dissipation of the TIP121 at case temperature 25°C?

The TIP121 has a maximum collector power dissipation (P_C) of 65 W when the case temperature (T_C) is maintained at 25°C, as stated in the Thermal Characteristics table on page 2 of the datasheet. This rating assumes proper heatsinking and declines linearly above 25°C per the derating curve in Figure 5.

TIP121 Specifications

Product attributes: Attribute value

Manufacturer:: onsemi

Series:: -

Package/Case:: TO-220-3

Packaging:: Bulk

Product Status:: Obsolete

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-220-3

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.

Tech Hub

2026-09-09 Counterfeit Electronic Components: How to Detect, Authenticate, and Test Suspect Parts

Counterfeit components can hide behind convincing markings and passing basic function tests. This engineering reference covers source traceability, external inspection, X-ray, XRF, electrical testing, …

2026-09-08 Obsolete Electronic Components: How to Source and Evaluate Replacements

A practical engineering and sourcing framework covering lifecycle verification, lifetime-buy calculations, replacement qualification, supplier checks and counterfeit-risk controls.

2026-09-07 TTL vs CMOS Logic Levels: 74HC and 74HCT Compatibility Explained

TTL and CMOS logic families differ in thresholds, loading, output drive, power and timing. This engineering guide compares 74HC and 74HCT, calculates noise margins and checks 3.3 V/5 V compatibility.

2026-09-04 Logic Level Shifter: How to Connect 3.3V and 5V Logic Safely

A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.

2026-09-03 74HC595 vs TPIC6B595: Output Drive, Pinout, Current, and Load Selection

The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…

2026-09-02 74HC595 Pinout, Timing, Output Current, and Applications

The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…

2026-09-01 Latch vs Flip-Flop: Timing, Differences and Design Choices

A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…

2026-08-30 D Latch Circuit: Truth Table, Timing, ICs and Applications

A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …

2026-08-28 SR Latch Explained: NOR and NAND Circuits, Truth Tables, and Applications

An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…

2026-08-27 Latch Circuit: SR and D Latches, Truth Tables, Timing, and Applications

Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…