onsemi TIP125

Overview

TIP125 from ON Semiconductor is a PNP epitaxial Darlington transistor designed for medium-power linear and switching applications, featuring -60 V collector-emitter sustaining voltage, -5 A DC collector current, and 65 W collector dissipation at TC = 25°C. It operates as a high-gain power switch in industrial motor controls, relay drivers, and lamp dimmers where robust current amplification and thermal stability are required.

For engineers reviewing the TIP125 datasheet, pinout, applications, or equivalent options, key selection criteria include its TO-220 package mechanical compatibility, guaranteed hFE ≥ 1000 at IC = -3 A, VCE(sat) ≤ -2 V at IC = -3 A/IB = -12 mA, and safe operating area validated up to 5 ms pulse width.

Technical Context

The TIP125 integrates two PNP transistors in Darlington configuration with internal base-emitter resistors (R1 ≈ 8 kΩ, R2 ≈ 0.12 kΩ), enabling high DC current gain without external bias components. Its complementary pairing with TIP120 series allows matched design of push-pull output stages.

It operates under junction temperatures up to 150°C and supports pulsed collector currents up to -8 A, with thermal derating beginning at TC > 25°C per the published power derating curve. The device exhibits Cob = 300 pF at VCB = -10 V, f = 0.1 MHz, influencing high-frequency switching behavior.

Key Specifications

Pinout & Package

Package: TO-220 3L (Single Gauge), through-hole, thermally enhanced plastic case with metal tab electrically connected to collector.

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 TIP125 offers optimal balance of through-hole manufacturability, 60 V blocking capability, and 5 A continuous current handling-making it preferred for cost-sensitive industrial controls where board real estate and legacy assembly processes constrain alternatives.

Availability

TIP125 is available at Aetrix Electronics and suitable for industrial motor control, relay/solenoid driving, and linear regulator pass applications requiring stable component supply and long-term production continuity.

Supply support for TIP125 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 energy-efficient power, analog, sensor, and connectivity solutions for automotive, industrial, cloud, consumer, and medical markets.

The TIP125 belongs to ON Semiconductor's legacy power bipolar transistor product line, originally developed by Fairchild Semiconductor to deliver rugged, high-gain switching performance in cost-sensitive industrial and appliance applications.

FAQ

What is the maximum continuous collector current rating for the TIP125?

The TIP125 has a maximum DC collector current rating of -5 A when operated with case temperature maintained at 25°C and proper heatsinking. This rating decreases with rising case temperature per the published thermal derating curve, reaching zero at TC = 150°C. For reliable long-term operation, design margins should account for ambient temperature, airflow, and heatsink thermal resistance to ensure TJ remains within the 150°C limit.

Does the TIP125 require an external base resistor?

Yes, the TIP125 requires an external base resistor to limit base current and prevent damage during turn-on. Although it contains internal base-emitter resistors (R1 ≈ 8 kΩ, R2 ≈ 0.12 kΩ), these do not replace the need for a series resistor between the driving source and the base terminal. Typical values range from 220 Ω to 1 kΩ depending on drive voltage and desired collector current, ensuring IB stays within the -120 mA absolute maximum rating.

Is the TIP125 pin-compatible with the TIP120 series?

No, the TIP125 is not pin-compatible with the TIP120 series because they are complementary devices: TIP125 is PNP while TIP120 is NPN. Their pinouts are mirror-inverted-TIP125 pin 1 is Base, pin 2 is Collector, pin 3 is Emitter; TIP120 uses the same physical TO-220 pinout numbering but functions as a high-side switch versus TIP120's low-side configuration. Interchanging them without circuit redesign will result in non-functional or damaged operation.

What is the typical VCE(sat) of the TIP125 at full rated current?

The TIP125 exhibits a maximum VCE(sat) of -2 V at IC = -3 A and IB = -12 mA, and -4 V at IC = -5 A and IB = -20 mA. These values represent worst-case saturation voltages under specified test conditions; typical units perform better, but design must use the maximum values for thermal and efficiency calculations. At -5 A, the resulting conduction loss exceeds 20 W, necessitating substantial heatsinking for continuous operation.

Can the TIP125 be used in linear regulator applications?

Yes, the TIP125 is suitable for linear regulator pass element applications due to its high hFE (≥1000), low VBE(on) (-2.5 V at IC = -3 A), and ability to sustain continuous collector current up to -5 A with appropriate thermal management. Its Darlington configuration provides excellent current amplification for error amplifier feedback loops, though designers must account for the higher VBE drop compared to single transistors and ensure adequate SOA compliance during dropout and transient conditions.