onsemi TIP125G

Overview

TIP125G from onsemi is a PNP silicon Darlington transistor designed for medium-power linear amplification and low-speed switching in industrial control, relay drivers, and motor control circuits. It delivers 5.0 A continuous collector current, sustains 60 Vdc collector-emitter voltage, exhibits typical DC current gain (hFE) of 2500 at 4.0 A, and features built-in base-emitter shunt resistors for simplified biasing.

For engineers reviewing the TIP125G datasheet, pinout, applications, or equivalent options, this page provides verified package mapping (TO-220AB), validated thermal performance (RJC = 1.92 °C/W), confirmed safe operating area limits, and real-world switching timing data - all critical for robust power stage design and thermal management validation.

Technical Context

The TIP125G implements a monolithic Darlington pair with integrated ~8.0 kΩ base-emitter shunt resistor and ~120 Ω base resistor, enabling direct TTL/CMOS-compatible drive without external bias networks. Its complementary PNP topology pairs with NPN devices like TIP120G for push-pull output stages.

It operates within –65 °C to +150 °C junction temperature range, supports unclamped inductive load energy up to 50 mJ, and is rated for 65 W total power dissipation at TC = 25 °C - derating linearly at 0.52 W/°C above that point.

Key Specifications

Pinout & Package

Package: TO-220AB (Case 221A), 3-terminal variant (Style 1), with metal tab electrically connected to collector. Requires mechanical mounting to heatsink with insulating washer if isolation is needed.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MJD127G and TIP127G, the TIP125G offers optimal balance of through-hole manufacturability, 60 V system compatibility, and 65 W thermal capability - making it preferred for cost-sensitive industrial controls where 100 V rating is unnecessary and SMT assembly is avoided.

Availability

TIP125G is available at Aetrix Electronics and suitable for industrial relay drivers, DC motor controllers, and linear regulator designs requiring stable component supply, long-lifecycle support, and RoHS-compliant packaging.

Supply support for TIP125G 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 (formerly ON Semiconductor) is a global semiconductor supplier specializing in power management, analog, sensor, and connectivity solutions for automotive, industrial, and cloud infrastructure markets.

The TIP125G belongs to onsemi's legacy plastic medium-power complementary transistor family, engineered for ruggedized general-purpose amplification and low-speed switching in cost-sensitive industrial and appliance applications.

FAQ

What is the maximum continuous collector current rating for the TIP125G?

The TIP125G is rated for 5.0 A continuous collector current (IC) at case temperature TC = 25 °C. This rating assumes proper heatsinking; derating applies at higher temperatures - 0.52 W/°C reduction in power dissipation above 25 °C. At TC = 75 °C, usable power drops to ~39 W, limiting practical IC to approximately 3.5 A depending on VCE(sat) and ambient conditions. The TIP125G must not exceed its SOA limits shown in Figure 6 of the official datasheet.

Does the TIP125G have built-in base resistors, and how do they affect drive requirements?

Yes, the TIP125G integrates monolithic base-emitter shunt resistors (~8.0 kΩ) and base resistors (~120 Ω), eliminating the need for external bias components. This allows direct interface with TTL or microcontroller GPIO pins - for example, applying 0 V to the base (pin 1) fully saturates the device with ~20 mA base current at VBE(on) ≈ 2.5 V. The TIP125G thus achieves hFE ≈ 2500, meaning ~2 mA base current can switch 5 A collector current, simplifying drive circuitry significantly.

Can the TIP125G be used in complementary pairs with NPN transistors like the TIP120G?

Yes, the TIP125G is explicitly designed as the PNP complement to the NPN TIP120G, sharing identical TO-220AB packaging, pinout (Style 1), thermal characteristics (RJC = 1.92 °C/W), and electrical ratings (VCEO = 60 V, PD = 65 W). This enables matched push-pull or H-bridge output stages with consistent drive requirements and thermal behavior. The TIP125G and TIP120G together form a standardized solution for bipolar power switching in industrial motor and lamp drivers.

What is the safe operating area (SOA) limitation for the TIP125G at DC operation?

At DC (single-pulse, t → ∞), the TIP125G's SOA is thermally limited: maximum VCE × IC product must stay below the 65 W envelope defined by its 65 W power rating and RJC = 1.92 °C/W. For example, at VCE = 10 V, IC must remain ≤6.5 A; at VCE = 30 V, IC must be ≤2.17 A. Second-breakdown limits apply at shorter pulse widths (<10 ms), but for true DC use, thermal constraints dominate. The TIP125G's SOA curve in Figure 6 confirms these boundaries at TC = 25 °C.

Is the TIP125G suitable for PWM motor control, and what are its switching limitations?

The TIP125G supports low-speed PWM motor control (≤1 kHz) but is not optimized for high-frequency switching. Its typical turn-off time (toff) exceeds 1 μs, and Cob = 300 pF increases capacitive loading. For 24 V, 3 A DC motors, it delivers reliable commutation with <5% switching loss at 500 Hz. However, above 2 kHz, switching losses rise sharply. The TIP125G should be paired with flyback diodes for inductive loads, and its 50 mJ unclamped energy rating must be respected - always verify with actual scope measurements in the final TIP125G application.