onsemi TIP125TU

Overview

TIP125TU from ON Semiconductor is a PNP epitaxial Darlington transistor in TO-220 package, rated for -60 V V_CEO, -5 A I_C (DC), and 65 W power dissipation at T_C = 25°C; it delivers high DC current gain (h_FE ≥ 1000 at I_C = -0.5 A) and low saturation voltage (-2 V at I_C = -3 A, I_B = -12 mA), used in medium-power linear and switching applications such as motor drivers and relay interfaces.

For engineers reviewing the TIP125TU datasheet, pinout, applications, or equivalent options, key selection considerations include its PNP Darlington architecture, -60 V/–5 A rating, TO-220 thermal performance, complementary pairing with TIP120 series, and suitability for industrial load switching where high β and robust SOA are required.

Technical Context

The TIP125TU integrates two PNP transistors in Darlington configuration with internal base-emitter resistors (R₁ ≈ 8 kΩ, R₂ ≈ 0.12 kΩ), enabling high input impedance and simplified drive requirements. It operates with V_EB(on) ≈ -2.5 V at I_C = -3 A and exhibits Cob = 300 pF at V_CB = -10 V, f = 0.1 MHz.

Its safe operating area supports pulsed operation up to I_CP = -8 A (pulse width ≤ 300 μs, duty cycle ≤ 2%), and thermal derating begins above T_C = 25°C, maintaining 65 W dissipation only at case temperature ≤ 25°C.

Key Specifications

Pinout & Package

Package: TO-220 3L (Single Gauge), through-hole, thermally enhanced plastic housing with metal tab electrically connected to collector. Mounting requires insulating washer unless collector is at system ground potential.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD127G and TIP145, the TIP125TU offers optimal balance of through-hole manufacturability, -60 V rating matched to common 24–48 V industrial rails, and lowest V_CE(sat) among TO-220 PNP Darlingtons at mid-load currents, making it preferred for cost-sensitive, thermally managed linear and switching loads.

Availability

TIP125TU is available at Aetrix Electronics and suitable for DC motor control, relay driving, and linear regulator pass element applications requiring stable component supply, long-term industrial lifecycle support, and consistent TO-220 mechanical compatibility.

Supply support for TIP125TU 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, sensors, and discrete devices for automotive, industrial, and cloud power applications.

The TIP125TU belongs to ON Semiconductor's legacy high-voltage bipolar transistor product line, originally developed by Fairchild Semiconductor to serve industrial linear and switching applications demanding ruggedness, high gain, and proven thermal reliability in TO-220 format.

FAQ

What is the maximum continuous collector current rating for the TIP125TU?

The TIP125TU has a maximum continuous collector current (I_C) rating of -5 A at T_C = 25°C. This rating assumes adequate heatsinking to maintain case temperature at or below 25°C. Derating is required above this temperature per the published thermal curve, and pulsed operation up to -8 A is permitted under strict conditions (pulse width ≤ 300 μs, duty cycle ≤ 2%). The TIP125TU must not be operated beyond these limits to ensure reliability and prevent thermal failure.

Is the TIP125TU pin-compatible with the TIP120 series?

Yes, the TIP125TU is complementary-not pin-compatible-to the TIP120 series. Both share identical TO-220 3L package and pinout (Base–Collector–Emitter), but the TIP125TU is PNP while the TIP120 is NPN. This allows direct pairing in push-pull or H-bridge topologies without layout changes, provided polarity and biasing are correctly implemented. The TIP125TU matches TIP120's electrical envelope in gain, voltage, and current ratings, enabling symmetrical design.

What is the typical DC current gain (h_FE) of the TIP125TU and at what conditions is it specified?

The TIP125TU guarantees a minimum DC current gain (h_FE) of 1000 at V_CE = -3 V and I_C = -0.5 A, and also maintains h_FE ≥ 1000 at V_CE = -3 V and I_C = -3 A. This high, stable gain across a wide current range reduces required base drive current and improves control precision in both linear and saturated switching modes. The TIP125TU's Darlington architecture inherently delivers this gain without external components.

Does the TIP125TU have built-in protection features such as base-emitter shunt resistors?

Yes, the TIP125TU includes internal base-emitter resistors: R₁ ≈ 8 kΩ between base and emitter, and R₂ ≈ 0.12 kΩ between base and collector. These resistors provide inherent turn-off biasing, suppress leakage-induced false triggering, and improve switching consistency-especially important in noisy industrial environments. Unlike bare transistors, the TIP125TU does not require external pull-down resistors for reliable off-state behavior.

Can the TIP125TU be used in linear regulator applications, and what thermal considerations apply?

Yes, the TIP125TU is commonly used as a pass transistor in negative linear regulators. Its 65 W power dissipation at T_C = 25°C supports substantial voltage drops, but thermal design is critical: junction temperature must remain ≤ 150°C. With R_θJC ≈ 1.9°C/W (derived from P_C/ΔT), a heatsink with R_θSA ≤ 5°C/W is recommended for 3 A loads at 10 V drop. The TIP125TU's high h_FE ensures stable regulation even under light loads.