onsemi BD243B

Overview

BD243B from Fairchild Semiconductor is an NPN epitaxial silicon power transistor in TO-220 package, rated for 80 V V_CEO, 6 A DC collector current, and 65 W collector dissipation at T_C = 25°C, used in medium-power linear regulators and switching applications such as motor drivers and power supplies.

For engineers reviewing the BD243B datasheet, pinout, applications, or equivalent options, key selection criteria include V_CEO = 80 V, I_C = 6 A, 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 TO-220 thermal performance under continuous and pulsed operation.

Technical Context

The BD243B 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. Its V_CEO(sus) = 80 V and I_C = 6 A define its safe operating area in DC and pulsed modes (PW = 300 µs, duty < 20%).

Thermal design relies on case-mounted heatsinking: P_C derates linearly above 25°C case temperature, with T_J(max) = 150°C and T_STG = –65 to 150°C. V_BE(on) = 2 V at I_C = 6 A confirms base drive requirement for full conduction.

Key Specifications

Pinout & Package

BD243B uses the standard TO-220 package with metal tab connected to Collector, enabling direct heatsink mounting. Package outline dimensions are fully specified per Fairchild Rev. A (Feb 2000) mechanical drawing.

Key Features

Applications

Equivalent & Alternatives

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

Compared with BD243B, MJD243G trades thermal capacity for footprint reduction, while BD243C extends voltage headroom without altering drive or thermal design-making BD243B optimal for cost-sensitive 24–48 V switching and linear applications requiring 80 V rating.

Availability

BD243B is available at Aetrix Electronics and suitable for DC motor control, linear power supplies, audio amplifier output stages, and relay/LED driver circuits requiring stable component supply and long-term industrial availability.

Supply support for BD243B 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 designer and manufacturer of analog and discrete semiconductors, acquired by ON Semiconductor in 2016; known for robust power transistors and wide-temperature-rated components.

The BD243B belongs to Fairchild's BD243/A/B/C family of medium-power NPN transistors, engineered for industrial-grade linear regulation and switching in motor drives, power supplies, and audio systems where reliability and thermal stability are essential.

FAQ

What is the maximum collector-emitter voltage rating for BD243B?

The BD243B has a maximum collector-emitter voltage rating (V_CEO) of 80 V at T_C = 25°C. This value is confirmed in the Absolute Maximum Ratings table and matches its V_CEO(sus) specification under I_C = 30 mA, I_B = 0 test condition. Exceeding this voltage risks avalanche breakdown and permanent device failure.

Is BD243B pin-compatible with BD243C?

Yes, BD243B is pin-compatible with BD243C - both use identical TO-220 package, terminal numbering (1=Base, 2=Collector, 3=Emitter), and mechanical footprint. The only difference is V_CEO (80 V vs. 100 V); all other electrical and thermal parameters including pinout, h_FE, and V_CE(sat) are identical per Fairchild Rev. A datasheet.

What base current is required to fully saturate BD243B at 6 A collector current?

To fully saturate BD243B at I_C = 6 A, the datasheet specifies V_CE(sat) ≤ 1.5 V tested at I_B = 1 A. Therefore, BD243B requires a minimum base current of 1 A for guaranteed saturation. Using less than 1 A may result in elevated V_CE and excessive power dissipation during switching.

Can BD243B be used in linear regulator applications?

Yes, BD243B is explicitly qualified for medium-power linear applications per its "Medium Power Linear and Switching Applications" designation. Its 65 W power dissipation at T_C = 25°C, h_FE ≥ 30 at low I_C, and stable V_BE(on) = 2 V make it suitable as a series pass transistor in adjustable linear regulators up to 5 A output.

What is the junction-to-case thermal resistance (R_θJC) of BD243B?

The BD243B datasheet does not specify R_θJC numerically, but its TO-220 package and 65 W P_C rating at T_C = 25°C imply typical R_θJC ≈ 1.9°C/W. This value is derived from R_θJC = (T_J(max) − T_C) / P_C = (150 − 25) / 65 ≈ 1.92°C/W - consistent with industry-standard TO-220 power transistors.