onsemi TIP122

Overview

TIP122 from ON Semiconductor is an NPN epitaxial Darlington transistor designed for medium-power linear and switching applications, featuring 100 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, lamp dimmers, and relay interface circuits.

For engineers reviewing the TIP122 datasheet, pinout, applications, or equivalent options, key selection considerations include its 100 V V_CEO(sus), 1000 minimum h_FE at I_C = 0.5 A, 2.0 V V_CE(sat) at I_C = 3 A / I_B = 12 mA, TO-220 package thermal performance, and complementary PNP pairing with TIP127.

Technical Context

The TIP122 integrates two cascaded NPN transistors with internal base-emitter resistors (R₁ ≈ 8 kΩ, R₂ ≈ 0.12 kΩ) to achieve high DC current gain (h_FE ≥ 1000) while maintaining stable saturation behavior. Its Darlington configuration enables low base drive requirements-12 mA base current suffices to saturate at 3 A collector load.

It operates within a junction temperature range of –65°C to +150°C and supports pulse currents up to 8 A (I_CP) under defined duty cycle constraints (pulse width ≤ 300 μs, duty ≤ 2%). Thermal derating begins above 25°C case temperature per the published power derating curve.

Key Specifications

Pinout & Package

Package: TO-220 3L (Single Gauge), through-hole, vertical mounting with metal tab electrically connected to collector. Standard lead assignment: Pin 1 = Base, Pin 2 = Collector (tab), Pin 3 = Emitter.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD122G and TIP127, the TIP122 offers superior thermal handling in through-hole designs, direct compatibility with legacy TO-220 heatsinks, and simplified unipolar switching implementation-making it optimal for prototyping, industrial controls, and medium-power analog systems where reliability and serviceability are prioritized.

Availability

TIP122 is available at Aetrix Electronics and suitable for DC motor control, lamp dimming, relay driver, and linear regulator pass element applications requiring stable component supply and long-term industrial availability.

Supply support for TIP122 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 (now onsemi) is a global semiconductor manufacturer specializing in energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The TIP122 belongs to the TIP12x family of medium-power Darlington transistors engineered for robust, cost-effective switching and linear regulation in industrial controls, power supplies, and electromechanical interfaces.

FAQ

What is the maximum safe collector-emitter voltage for the TIP122?

The TIP122 has a collector-emitter sustaining voltage (V_CEO(sus)) of 100 V, tested under I_C = 100 mA and I_B = 0. This is the maximum voltage the device can block in active or saturated mode without breakdown. Exceeding this rating risks permanent damage, especially during inductive load switching where voltage spikes may occur.

Can the TIP122 be driven directly from a 3.3 V microcontroller GPIO?

No-the TIP122 requires a minimum V_BE(on) of 2.5 V at I_C = 3 A, and its Darlington structure demands sufficient base current (e.g., 12 mA at I_C = 3 A). A 3.3 V GPIO typically cannot source enough current without a series base resistor or level-shifting buffer; 5 V logic or dedicated driver ICs are recommended for reliable saturation of the TIP122.

Is the metal tab on the TIP122 electrically isolated?

No-the metal tab of the TIP122 in TO-220 package is internally connected to the collector terminal (Pin 2). When mounted to a heatsink, the heatsink becomes part of the collector circuit. Electrical isolation requires insulating hardware (e.g., mica washer, silicone pad) and isolated mounting screws to prevent short circuits in grounded-chassis systems.

What is the safe operating area (SOA) limitation for the TIP122 at 100 V V_CE?

Per the SOA graph in the official datasheet, the TIP122 supports ≤100 mA continuous collector current at V_CE = 100 V in DC operation. At higher currents, voltage must be reduced to stay within the second breakdown boundary-e.g., 1 A is limited to ~10 V, and 3 A to ~3 V. Pulse operation extends these limits under strict duty-cycle constraints.

How does the TIP122 differ from the TIP120 and TIP121?

The TIP122 differs from the TIP120 and TIP121 solely in voltage ratings: TIP120 has V_CEO(sus) = 60 V, TIP121 = 80 V, and TIP122 = 100 V. All share identical package (TO-220), pinout, h_FE ≥ 1000, I_C = 5 A, and thermal characteristics. Substituting TIP122 for TIP120/TIP121 is safe if voltage margin is needed-but not vice versa in high-voltage applications.