Onsemi BD243CG NPN Power Transistor: Datasheet, Application Circuits, and Replacement Guide
The BD243CG from Onsemi is a robust and widely used NPN power transistor designed for medium-power linear and switching applications. Housed in the classic TO-220 package, it serves as a fundamental building block in power supply circuits, audio amplifiers, and motor control systems. This article provides a detailed overview of its specifications, practical application circuits, and suitable replacement options.
Datasheet Overview and Key Specifications
The BD243CG is part of a series (BD241-242-243) that offers varying voltage ratings. The "CG" suffix denotes a higher voltage variant. Its primary function is to amplify current, allowing a small input signal to control a much larger output current. Key absolute maximum ratings from its datasheet include:
Collector-Emitter Voltage (VCEO): 100 V
Collector Current (IC): 6 A
Power Dissipation (PD): 65 W (at case temperature TC = 25°C)
DC Current Gain (hFE): 15 to 75 (at IC = 2 A, VCE = 4 V)
These ratings indicate a component capable of handling significant power levels. The relatively low saturation voltage ensures efficient switching operation. For reliable performance, it is crucial to mount the transistor on an adequate heatsink to manage thermal dissipation, especially when operating near its maximum limits.
Application Circuits
The BD243CG is versatile and can be configured in several ways. Two classic circuit examples are:
1. Linear Regulator / Series Pass Transistor:
In this configuration, the BD243CG acts as a variable resistor to regulate output voltage. A control IC or a zener diode provides a stable reference voltage to the base. The transistor handles the high current required by the load, making it an excellent choice for building simple and robust linear power supplies with output currents of several amps.
2. Class AB Audio Amplifier Output Stage:
The BD243CG is well-suited for the output stage of audio power amplifiers. In a push-pull pair with its PNP complement, the BD244CG, it can deliver dozens of watts of audio power to a speaker. Its linear characteristics in the operating region help in achieving low distortion audio output.
3. Simple Switch for Motor or Relay Control:
As a low-side switch, the transistor is used to control heavier loads like DC motors or relays. A small signal from a microcontroller or logic circuit (typically through a current-limiting base resistor) turns the transistor on or off. When saturated, it allows nearly the full supply voltage to be applied to the load, making it an efficient driver for inductive loads.
Replacement Guide and Equivalents
The BD243CG remains a common part, but identifying a suitable substitute may be necessary for repair or design flexibility.
Direct Equivalents: The best replacements are devices from the same series with equal or better ratings. The BD243C (without the "G") and the higher-powered BD243D are often direct drop-in replacements. The BD244CG (PNP) and BD245CG (NPN) are also closely related variants.
Popular Cross-References: Common equivalents from other manufacturers include the TIP31C (a very common general-purpose power transistor), 2SD717, and 2SC5200 (the latter for higher-performance audio applications).
Important Considerations When Replacing:
Verify Pinout (E-B-C): While the TO-220 pinout is often standard, always confirm the emitter-base-collector configuration.
Check Voltage and Current Ratings: Ensure the substitute's VCEO and IC ratings meet or exceed those of the original.
Consider Switching Speed: For high-frequency applications, the substitute's transition frequency (fT) should be comparable.
ICGOODFIND: The Onsemi BD243CG is a classic, versatile, and reliable workhorse for power electronics. Its strength lies in its robust construction, high power handling capability, and straightforward implementation in both linear and switching circuits. While newer MOSFETs may offer higher efficiency in switching applications, the BD243CG remains a top choice for designers and repair technicians for its simplicity, linearity, and cost-effectiveness in numerous analog and power control tasks.
Keywords: NPN Power Transistor, TO-220 Package, Current Amplifier, Linear Regulator, Switching Application.
