The BC490 is a high-current PNP transistor widely used in medium-power switching and amplification applications. With its 80-volt rating, 1-ampere collector current capability, and efficient low-saturation voltage, it serves as a versatile component suitable for both general-purpose electronic designs and more demanding control circuits. This article will discuss the key features, specifications, performance details, and practical applications of the BC490 transistor.

Catalog

BC490 PNP Transistors Overview

The BC490 is a high-current PNP bipolar junction transistor designed for medium-power switching and amplification. With an 80 V voltage rating and up to 1 A collector current, it offers reliable performance in general-purpose applications. Its low saturation voltage and TO-92 package make it suitable for compact circuits that require efficient current flow and stable thermal behavior.

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Pinout Configuration

Alternatives & Equivalents

BC488

BC558B

MPSA92

2N5401

BC177

2N3906

BC490 Transistors Specifications

BC490 Electrical Characteristics

BC490 Switching Time Test Circuits

The BC490 switching time test circuits illustrate how the transistor behaves during turn-on and turn-off conditions. In the turn-on test, a positive input pulse drives the base through a coupling capacitor and resistor network, allowing the transistor to transition from cutoff to saturation. The collector is connected to a +40 V supply through a load resistor, and the resulting output waveform shows how quickly the transistor can conduct when the base receives a triggering signal. This setup allows measurement of delay time, rise time, and overall turn-on performance.

In the turn-off test, a reverse-bias voltage is applied to the base through similar components, forcing the transistor out of saturation. The input pulse removes drive from the base, and the output signal reveals the delay and fall times as the transistor switches off. By using identical load and timing conditions, these circuits provide a consistent method for evaluating how efficiently the BC490 can operate in high-speed switching applications.

BC490 Typical Characteristics Curves

The current-gain bandwidth product curve shows how the transistor’s high-frequency performance varies with collector current. As the current increases, the gain-bandwidth product rises to a peak, indicating the optimal operating region for fast switching or high-frequency amplification. Beyond this point, the product gradually decreases as higher currents introduce limitations in device speed. The graph helps designers choose the most efficient operating current when high-frequency response is important.

The capacitance curve illustrates how junction capacitances (Cibo and Cobo) decrease as the reverse voltage increases. Higher reverse bias reduces the width of the depletion region, lowering capacitance and improving switching speed. This behavior is typical for BJTs and is important for circuits where input and output capacitances affect response time or high-frequency stability.

The collector saturation region graph demonstrates how the collector-emitter saturation voltage (VCE(sat)) varies with collector current across different base currents. Lower V_CE(sat) at higher base drive indicates more efficient saturation, which is essential for low-loss switching applications. This curve helps determine the required base current to achieve deep saturation at a given load.

The base-emitter temperature coefficient curve shows how the VBE voltage drops as temperature increases. The negative temperature coefficient becomes less pronounced at higher collector currents, illustrating the thermal behavior of the junction. This is useful for understanding bias stability and for designing temperature-compensated circuits.

BC490 Transistors Application Circuit

The diagram shows two simple switching circuits using BC490 transistors to control LEDs. In the left circuit, resistors R1 and R2 provide enough base current to turn Q1 on. When the base–emitter junction becomes forward-biased, the transistor conducts, allowing current to flow from the 12-volt supply through the collector–emitter path and then through the LED and its series resistor. As a result, LED D1 lights up, and the meters confirm that current is flowing. This demonstrates how the BC490 can act as a switch, activating a load whenever the base receives sufficient drive.

In the right circuit, the base of Q2 does not receive enough current through resistors R4 and R5, so the transistor remains off. Because the collector–emitter path is not conducting, no current reaches LED D2, leaving it dark and showing zero readings on the meters. This side of the diagram illustrates the opposite condition: without adequate base bias, the transistor blocks the current and the load stays off. Together, the two circuits clearly show how a BC490 transistor can be used as a simple on/off control element.

BC490 Transistors Applications

Switching circuits – used to turn LEDs, relays, or small loads on and off.

Low-power amplification – suitable for amplifying small signals in audio or sensor circuits.

General-purpose NPN driver – can be used to drive other components such as buzzers or small DC motors.

Signal processing – works in basic analog stages like pre-amplifiers or small-signal conditioning circuits.

Digital interfacing – used to interface low-voltage control signals with higher-voltage loads.

Transistor logic circuits – applied in simple logic gates, timing circuits, or switching networks.

Voltage level shifting – helps shift control signals between different voltage levels.

LED indicators – ideal for controlling indicator lights with current-limiting resistors.

Mechanical Dimensions

BC490 Manufacturer

ON Semiconductor (onsemi) company’s capabilities for BC490 device included consistent semiconductor processing, robust quality control, and production of through-hole TO-92 packages suited for consumer electronics, industrial controls, and educational circuits. Onsemi engineered the BC490 to handle moderate voltage and current levels, making it useful for tasks such as driving LEDs, relays, and small loads, while maintaining stable gain and dependable performance across a wide range of operating conditions.