The BC337 NPN epitaxial silicon transistor is a widely used, general-purpose discrete device favored for switching and small-signal amplification. Housed in a compact TO-92 package and manufactured by Fairchild/onsemi. This article will discuss the BC337’s core specifications, pinout and CAD models, typical circuit functions and more.

Catalog

BC337 NPN Transistor Basic

The BC337 is an NPN general-purpose transistor widely used for switching and small-signal amplification. Produced by Fairchild/onsemi, it comes in a compact TO-92 package and provides reliable performance. With a collector-emitter voltage of 45 V, collector current up to 800 mA, and power dissipation around 625 mW, it suits many medium-load driving tasks.

In addition, the BC337 is available in gain-sorted versions - BC337-16, BC337-25 , and BC337-40 - offering hFE ranges from 100 to over 600, making it adaptable for various amplification levels. Its typical 100 MHz transition frequency allows for clean operation in low-to-mid-frequency circuits.

If you are interested in purchasing the BC337, feel free to contact us for pricing and availability.

BC337 Transistor CAD Models

BC337 Transistor Pinout Config

BC337 Alternatives & Equivalents

BC337 Transistor Specifications

BC337 Working in Circuit

BC337 as a Transistor Amplifier in a Filtered Output Stage

In the first circuit, the BC337 acts as a common-emitter amplifier driven by a network of RC filters (R1–R4 and C1–C3). These filters shape the signal before it reaches the base of the BC337, allowing only the desired frequency components to modulate the transistor. When the filtered voltage at the base rises above about 0.7 V, the BC337 begins to conduct, pulling current through R6 and producing the amplified output at the collector. Capacitor C4 stabilizes the output by smoothing voltage variations, making the BC337 function as a responsive amplifier or signal-conditioning stage.

BC337 as a Switching Element in an Astable Multivibrator

In the second diagram, two BC337 transistors form a classic astable multivibrator, generating a continuous oscillating square-wave signal. Each BC337 alternately switches on and off as its base receives charging and discharging currents from the 100 µF capacitors. When one transistor switches on, it forces the other off due to the cross-coupled configuration. The BC337 therefore operates purely as a switch, turning fully on (saturation) and fully off (cut-off) to produce a blinking or oscillating output. The timing is controlled by the capacitors and the 12 kΩ resistors feeding the transistor bases.

BC337 as an LED Driver and Level Indicator

In the third circuit, each BC337 works as an LED driver for a level-indicator display. Individual input pins (J1–J5) apply signals to each transistor base. When a base receives a high signal, the BC337 switches on and allows current to flow through its respective LED and series resistor. This action lights the LED corresponding to a specific level (25%, 50%, 75%, 100%, or alarm). The BC337 operates as a low-side switch, sinking current from the LEDs to ground. Because BC337 can handle relatively high current, it ensures stable illumination even when multiple LEDs operate simultaneously.

BC337 Transistor Applications

-Switching low-to-medium power loads (LEDs, relays, buzzers, small motors)

-Signal amplification in audio, sensor, and small-signal stages

-Digital switching in microcontroller and logic-level interfaces

-Pulse generation and timing circuits (astable, monostable multivibrators)

-Low-side switching for power rails up to moderate current levels

-LED indicators and display drivers

-Voltage-level shifting between circuits

-Sensor interface circuits requiring current boosting

-General-purpose hobby electronics and prototyping projects

-Battery-powered devices needing efficient NPN switching elements