onsemi TIP126

Overview

TIP126 from onsemi is a PNP silicon Darlington power transistor in TO-220AB package, rated for 5.0 A continuous collector current, 80 V collector-emitter sustaining voltage (V_CEO(sus)), and 65 W power dissipation at T_C = 25°C - designed for low-speed switching and linear amplifier applications in industrial control and power regulation circuits.

For engineers reviewing the TIP126 datasheet, pinout, applications, or equivalent options, key selection criteria include its built-in base-emitter shunt resistors, high DC current gain (h_FE = 2500 typ. @ I_C = 4.0 A), low saturation voltage (V_CE(sat) ≤ 4.0 V @ I_C = 5.0 A), and thermal resistance (R_JC = 1.92 °C/W) - all critical for robust thermal management and drive-efficiency in relay drivers and motor controls.

Technical Context

The TIP126 implements a monolithic Darlington pair with integrated ~8.0 kΩ base-emitter shunt resistor and ~120 Ω base resistor, enabling simplified biasing without external components. Its PNP polarity and complementary pairing with NPN TIP121 define its role in push-pull output stages and dual-rail power switches.

It operates within –65°C to +150°C junction temperature range, supports unclamped inductive load energy up to 50 mJ, and exhibits Cob = 300 pF at V_CB = 10 V - confirming suitability for moderate-frequency switching below 100 kHz where capacitive loading and second-breakdown limits must be observed.

Key Specifications

Pinout & Package

Package: TO-220AB (Case 221A), 4-pin outline with pins 1–4 arranged vertically; pin 1 = Base, pin 2 = Collector, pin 3 = Emitter, pin 4 = Collector (dual-collector configuration for enhanced current handling and thermal path).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD127G and TIP146, the TIP126 offers optimal balance of through-hole manufacturability, integrated biasing, 80 V capability, and 65 W thermal performance - making it preferred for cost-sensitive, medium-power industrial controls where design simplicity and proven reliability are prioritized.

Availability

TIP126 is available at Aetrix Electronics and suitable for industrial relay drivers, DC motor speed control, linear power regulators, and overcurrent-protected power supplies requiring stable component supply and long-term production continuity.

Supply support for TIP126 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

onsemi is a global semiconductor manufacturer specializing in energy-efficient power, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The TIP126 belongs to onsemi's legacy plastic medium-power complementary transistor family, engineered for rugged, cost-effective linear amplification and low-speed switching in industrial automation and power management systems.

FAQ

What is the maximum continuous collector current rating for the TIP126?

The TIP126 has a maximum continuous collector current (I_C) rating of 5.0 A at case temperature T_C = 25°C. This rating decreases with rising case temperature due to its 0.52 W/°C power derating slope - meaning at T_C = 75°C, usable power drops to 39 W and corresponding I_C falls to approximately 3.5 A under typical V_CE conditions. Always verify thermal design using R_JC = 1.92 °C/W and ambient constraints.

Does the TIP126 include built-in base resistors?

Yes, the TIP126 features monolithic construction with built-in base-emitter shunt resistors (~8.0 kΩ) and base resistors (~120 Ω), as confirmed in Figure 1 of the onsemi datasheet. These integrated resistors eliminate the need for external bias components in most switching applications, simplifying drive circuitry and improving consistency across production units.

What is the collector-emitter sustaining voltage (V_CEO(sus)) specification for the TIP126?

The TIP126 has a minimum collector-emitter sustaining voltage V_CEO(sus) of 80 Vdc at I_C = 100 mAdc and I_B = 0, per the Electrical Characteristics table on page 2 of the onsemi datasheet. This parameter reflects its ability to block voltage under active switching conditions - distinct from static breakdown voltage - and confirms suitability for 24 V and 48 V industrial systems with transient margin.

Can the TIP126 be used as a direct replacement for the TIP125?

No, the TIP126 is not a direct replacement for the TIP125. While both are PNP Darlington transistors in TO-220AB packages, the TIP125 is rated for V_CEO(sus) = 60 V and P_D = 65 W, whereas the TIP126 is rated for V_CEO(sus) = 80 V and identical power dissipation. Substituting TIP126 for TIP125 is safe in higher-voltage designs, but replacing TIP126 with TIP125 risks overvoltage failure in 80 V-rated circuits.

What is the thermal resistance from junction to case (R_JC) for the TIP126?

The TIP126 has a maximum junction-to-case thermal resistance (R_JC) of 1.92 °C/W, as specified in the Thermal Characteristics table on page 2 of the onsemi datasheet. This value enables accurate heatsink sizing: for example, to maintain T_J ≤ 125°C at 40 W dissipation with T_C = 75°C, the required heatsink-to-ambient resistance must be ≤ 10.5 °C/W (calculated as (125 − 75)/40 − 1.92).