onsemi BD243A

Overview

BD243A from Fairchild Semiconductor is an NPN epitaxial silicon power transistor in TO-220 package, rated for 60 V V_CEO, 6 A DC collector current, and 65 W collector dissipation at T_C = 25°C, used in medium-power linear regulation and switching applications such as DC motor drivers and power supply output stages.

For engineers reviewing the BD243A datasheet, pinout, applications, or equivalent options, key selection factors include V_CEO = 60 V, h_FE ≥ 30 at I_C = 0.3 A, V_CE(sat) ≤ 1.5 V at I_C = 6 A / I_B = 1 A, and thermal derating above 25°C case temperature.

Technical Context

The BD243A operates as a medium-power NPN bipolar junction transistor with fixed three-terminal configuration (Base–Collector–Emitter), designed for linear amplification and hard-switching duty where low saturation voltage and stable DC current gain are required. It features a maximum junction temperature of 150°C and storage range from –65°C to +150°C.

Its safe operating area (SOA) is defined up to 10 ms pulse width with derated power above 25°C case temperature, and it exhibits V_BE(on) = 2.0 V at I_C = 6 A, supporting robust base drive design in high-current switching circuits.

Key Specifications

Pinout & Package

BD243A uses the standard TO-220 package with 3 leads: lead 1 = Base, lead 2 = Collector (electrically connected to metal tab), lead 3 = Emitter. The metal tab is electrically tied to the collector and must be isolated from heatsink unless circuit topology permits common-collector mounting.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BD243A, MJD243G trades package form factor and thermal performance for board density, while BD243C extends voltage headroom without altering footprint or drive requirements-making BD243C a drop-in upgrade for higher-voltage systems.

Availability

BD243A is available at Aetrix Electronics and suitable for DC motor control, linear power supplies, and audio amplifier output stages requiring stable component supply and long-term industrial availability.

Supply support for BD243A 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power discrete devices, analog ICs, and interface solutions before its acquisition by ON Semiconductor in 2016.

The BD243A belongs to Fairchild's BD24x series of medium-power NPN/PNP complementary transistors, engineered for cost-effective, thermally robust switching and linear applications in industrial and consumer power electronics.

FAQ

What is the maximum continuous collector current for BD243A?

The BD243A is rated for 6 A DC collector current at case temperature T_C = 25°C. This rating assumes adequate heatsinking; current must be reduced per the published power derating curve above 25°C. At T_C = 100°C, the usable I_C drops to approximately 3.2 A. The BD243A datasheet specifies this limit under DC conditions-not pulsed-so sustained 6 A operation requires active thermal management.

Is BD243A pin-compatible with BD243B or BD243C?

Yes, BD243A is fully pin-compatible with BD243B and BD243C: all share identical TO-220 package, 3-pin layout (Base–Collector–Emitter), and mechanical dimensions. The only differences are absolute maximum voltage ratings-V_CEO = 60 V for BD243A, 80 V for BD243B, and 100 V for BD243C-making BD243A a direct physical replacement where voltage stress remains below 60 V.

What is the typical V_CE(sat) of BD243A at full-rated current?

The BD243A exhibits V_CE(sat) ≤ 1.5 V when operated at I_C = 6 A and I_B = 1 A, per the datasheet's electrical characteristics table. This saturation voltage is measured under pulsed conditions (PW = 300 µs, duty cycle < 20%) to minimize self-heating. In DC operation, V_CE(sat) may rise slightly due to thermal effects, so actual design values should include margin for junction temperature rise.

Can BD243A be used as a direct replacement for BD243?

No-BD243A is not a direct replacement for BD243 in all cases. While both share the same package and pinout, BD243 has V_CEO = 45 V versus BD243A's 60 V. Using BD243A in a circuit originally designed for BD243 introduces unnecessary voltage margin but is electrically safe; however, substituting BD243 for BD243A risks breakdown if system voltage exceeds 45 V. Always verify voltage stress margins before interchange.

Does BD243A require a heatsink in normal operation?

Yes, BD243A requires a heatsink for any continuous operation above ~1.5 A at room ambient, due to its 65 W power dissipation limit at T_C = 25°C. Without heatsinking, the TO-220 package's thermal resistance (junction-to-case ≈ 1.9°C/W) causes rapid junction temperature rise. For example, at I_C = 3 A and V_CE = 2 V, power dissipation is 6 W-requiring at least a 10°C/W heatsink to maintain T_J < 125°C.