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BC337 Transistor: Pinout, Equivalents, and Applications

Introduction to the BC337 Transistor

The BC337 is a common NPN bipolar junction transistor (BJT) widely used in electronics for switching and amplification purposes. This general-purpose transistor is known for its reliability, low cost, and versatility in various applications. In this comprehensive article, we will explore the BC337 transistor’s pinout, specifications, equivalent transistors, and practical applications.

BC337 Transistor Pinout

The BC337 transistor has a TO-92 package, which is a small plastic package with three leads. The pinout of the BC337 is as follows:

Pin Symbol Description
1 E Emitter
2 B Base
3 C Collector

The emitter is the source of electrons, the base controls the flow of electrons, and the collector is where the electrons flow to. It’s essential to identify the correct pinout when using the BC337 in your projects to ensure proper functionality.

BC337 Transistor Specifications

To effectively use the BC337 transistor, it’s crucial to understand its specifications. The following table highlights the key specifications of the BC337:

Parameter Value
Maximum Collector-Emitter Voltage 45 V
Maximum Collector Current 800 mA
Maximum Power Dissipation 625 mW
DC Current Gain (hFE) 100-400
Transition Frequency (fT) 100 MHz
Operating Temperature Range -65°C to 150°C

These specifications provide insights into the operating limits and characteristics of the BC337 transistor, helping you design circuits that operate within the transistor’s safe operating area.

BC337 Equivalent Transistors

In case the BC337 is unavailable or you need an alternative, several transistors can serve as equivalents. The following table lists some common BC337 equivalent transistors:

Equivalent Transistor Manufacturer
2N2222A Various
2N3904 Various
BC546 Various
BC547 Various
BC548 Various
BC549 Various

While these transistors have similar characteristics to the BC337, it’s essential to review their datasheets to ensure they meet your specific application requirements.

BC337 Transistor Applications

The BC337 transistor finds its way into numerous electronic applications due to its versatility and reliability. Let’s explore some common applications of the BC337:

1. Switching Circuits

One of the primary applications of the BC337 is in switching circuits. The transistor can be used to control the flow of current through a load, such as LEDs, relays, or motors. By applying a small current to the base, the transistor can switch on or off, allowing or blocking current flow through the collector-emitter path.

2. Amplification

The BC337 can also be used as an amplifier to increase the strength of weak signals. In common-emitter configuration, the transistor amplifies the input signal applied to the base, resulting in a larger output signal at the collector. This amplification property is useful in audio amplifiers, signal conditioning circuits, and sensor interfaces.

3. Logic Gates

Transistors like the BC337 can be used to construct basic logic gates, such as AND, OR, and NOT gates. By combining multiple transistors and resistors, complex digital circuits can be built, forming the foundation of digital electronics.

4. Current Regulation

The BC337 can be employed in current regulation circuits to maintain a constant current through a load. By controlling the base current, the transistor can adjust its resistance to maintain a specific collector current, irrespective of variations in the load or supply voltage.

5. Temperature Sensing

The BC337’s temperature-dependent characteristics can be leveraged to create temperature sensing circuits. By monitoring the changes in the transistor’s base-emitter voltage or collector current, temperature variations can be detected and used for temperature monitoring or control systems.

BC337 Transistor Circuit Examples

To better understand how the BC337 transistor can be used in practical circuits, let’s explore a couple of simple examples.

Example 1: LED Driver Circuit

In this example, the BC337 is used to control an LED based on an input signal:

          /  R1
         /   1k
      B |-----| Input Signal
      E |      BC337
          /  R2
         /   100
      C |-----| LED
       |      |>|
      GND    GND

When the input signal is high, the BC337’s base-emitter junction is forward-biased, allowing current to flow through the LED. When the input signal is low, the transistor is off, and the LED is turned off.

Example 2: Simple Amplifier

Here, the BC337 is configured as a common-emitter amplifier to amplify an input signal:

          /  R1
         /   10k
      C |-----| Output Signal
      B |-----| Input Signal
      E |      BC337

The input signal is applied to the base of the BC337, and the amplified output signal is obtained at the collector. The gain of the amplifier can be adjusted by changing the values of the resistors.

Frequently Asked Questions (FAQ)

1. What is the maximum collector current rating of the BC337 transistor?

The maximum collector current rating of the BC337 is 800 mA.

2. Can the BC337 transistor be used as a switch?

Yes, the BC337 can be used as a switch to control the flow of current through a load.

3. What is the pinout of the BC337 transistor?

The pinout of the BC337 in a TO-92 package is as follows: Pin 1 – Emitter, Pin 2 – Base, Pin 3 – Collector.

4. Is the BC337 suitable for high-frequency applications?

The BC337 has a transition frequency (fT) of 100 MHz, making it suitable for low to medium-frequency applications. For high-frequency applications, transistors with higher fT values may be more appropriate.

5. Can the BC337 be replaced with a BC547 transistor?

Yes, the BC547 is a common equivalent transistor for the BC337 and can be used as a replacement in most applications. However, it’s always recommended to review the datasheet to ensure compatibility.


The BC337 transistor is a versatile and widely used NPN bipolar junction transistor in electronics. With its reliable performance, low cost, and wide range of applications, the BC337 is a go-to choice for many engineers and hobbyists. Understanding its pinout, specifications, equivalent transistors, and practical applications empowers you to effectively utilize the BC337 in your projects. Whether you’re designing switching circuits, amplifiers, or digital logic gates, the BC337 transistor proves to be a valuable component in your electronic toolkit.