onsemi BDX53TU

Overview

BDX53TU from ON Semiconductor (formerly Fairchild) is an NPN epitaxial silicon Darlington transistor in TO-220 package, rated for 45 V V_CEO, 8 A continuous collector current, and 60 W power dissipation at T_C = 25°C. It integrates a built-in parallel diode and is designed for high-current linear and switching applications including hammer drivers and audio amplifiers.

For engineers reviewing the BDX53TU datasheet, pinout, applications, or equivalent options, key selection criteria include its 45 V blocking capability, 750 minimum h_FE at 3 A, 2.0 V V_CE(sat), integrated damper diode, and TO-220 thermal performance-critical for industrial motor control and relay driving circuits.

Technical Context

The BDX53TU operates as a medium-power NPN Darlington pair with monolithic integration of a clamping diode across C–E. Its DC current gain (h_FE) is specified ≥750 at V_CE = 3 V and I_C = 3 A, and saturation voltages are tightly characterized: V_CE(sat) ≤ 2.0 V and V_BE(sat) ≤ 2.5 V under same conditions.

Thermal design is enabled by its TO-220 package with case-to-ambient thermal resistance of ~3.5°C/W (typical, with 1 in² copper pad), supporting operation up to 150°C junction temperature. The integrated diode exhibits forward voltage of 1.8 V at 3 A and 2.5 V at 8 A, enabling snubber-free inductive load switching.

Key Specifications

Pinout & Package

BDX53TU is housed in a standard TO-220 package with 3 leads: Base (pin 1), Collector (pin 2), Emitter (pin 3). The metal tab is electrically connected to the collector and serves as the primary thermal path.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TIP122 and BDX53C, the BDX53TU provides the best combination of 45 V rating, integrated diode, and low saturation voltage for mid-voltage industrial switching-reducing component count without sacrificing reliability or thermal headroom.

Availability

BDX53TU is available at Aetrix Electronics and suitable for relay drivers, audio amplifiers, and DC motor controllers requiring stable component supply, long-term industrial lifecycle support, and traceable sourcing from authorized channels.

Supply support for BDX53TU 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 (formerly Fairchild Semiconductor) is a global semiconductor supplier focused on energy-efficient electronics, with leadership in power management, analog, and discrete devices.

The BDX53TU belongs to the legacy BDX53/A/B/C Darlington transistor family, originally designed for high-reliability industrial linear and switching power applications where integrated protection and thermal robustness are essential.

FAQ

What is the maximum continuous collector current rating for BDX53TU?

The BDX53TU has a maximum continuous collector current (I_C) rating of 8 A at case temperature T_C = 25°C. This rating decreases with rising case temperature per the derating curve in the datasheet, reaching zero at approximately 175°C. For reliable operation above 10 W dissipation, a heatsink is mandatory. The BDX53TU must be mounted with thermal compound and mechanical torque compliance to maintain safe junction temperatures.

Does BDX53TU include an integrated diode, and what is its forward voltage?

Yes, the BDX53TU integrates a monolithic damper diode between collector and emitter. Its forward voltage is 1.8 V at 3 A forward current and 2.5 V at 8 A, as measured under pulsed conditions. This diode enables self-contained flyback energy recirculation in inductive switching applications, eliminating the need for an external diode in most relay and solenoid driver designs. The BDX53TU's diode is not rated for continuous conduction but handles typical inductive transients.

What is the pin configuration of BDX53TU in TO-220 package?

The BDX53TU uses standard TO-220 pinout: Pin 1 is Base, Pin 2 is Collector (electrically connected to the metal tab), and Pin 3 is Emitter. When viewed with the flat side facing forward and leads pointing downward, pins are numbered left-to-right as 1–2–3. The metal tab must be electrically isolated from other circuit nodes unless intentionally used as the collector node and heatsink ground. Mounting hardware must avoid shorting the tab to adjacent traces.

How does BDX53TU compare to BDX53C in terms of voltage ratings and compatibility?

The BDX53TU has V_CEO = 45 V and V_CBO = 45 V, whereas BDX53C is rated for 100 V in both parameters. All other specifications-including package, pinout, h_FE, V_CE(sat), and thermal characteristics-are identical. The BDX53TU is not a drop-in replacement for BDX53C in 100 V systems, but BDX53C can replace BDX53TU where higher voltage margin is acceptable. Both share the same TO-220 footprint and soldering profile.

Is BDX53TU suitable for audio amplifier output stages, and what biasing considerations apply?

Yes, the BDX53TU is commonly used in Class-AB audio output stages due to its high h_FE (≥750 at 3 A), low V_CE(sat) (≤2.0 V), and thermal stability in TO-220. Biasing requires careful setting of quiescent current (typically 20–50 mA) using emitter resistors and V_BE multiplier networks to prevent thermal runaway. Because the BDX53TU's V_BE(sat) is 2.5 V at 3 A, driver stage headroom must accommodate this to ensure full turn-on without clipping.