KSC1845 NPN Transistor: Pinout, Datasheet, Equivalent and Uses

Published:January 18, 2024

Dr. James Anderson is a distinguished figure in electrical engineering, specialising in electronic components. Dr. Anderson has dedicated his career to pushing the boundaries of electronic component technology. With over 20 years of experience in academia and industry, he has earned a reputation as a leading expert.

In the expansive realm of electronic components, transistors function as miniature on/off switches, regulating the current flow and energizing myriad devices. Within this cadre of essential components, the KSC1845 NPN transistor stands out as a favored option due to its adaptability and user-friendly nature. In this article, we will delve into the KSC1845, exploring its pinout, specifications, equivalent, datasheet and practical applications. Everything you need to know about this transistor.



What is KSC1845?

The KSC1845 belongs to the NPN transistor family, specifically a bipolar junction transistor(BJT) packaged in TO-92 format and constructed with silicon semiconductor material. Within NPN transistors, there are two crucial junctions: the emitter-base and the collector-base.

Conduction in the transistor initiates when the emitter-base junction is forward-biased and the collector-base junction is reverse-biased, provided sufficient current exists at the base pin. The emitter-base junction can be brought into forward bias by applying a negative voltage to the emitter side and a positive voltage to the base side.

Comprising three layers, KSC1845 includes one p-doped layer and two n-doped layers. The p-doped layer represents the base terminal, while the two n-doped layers correspond to the connection and emitter.

This component features three terminals: base, collector, and emitter. Electrons are emitted from the emitter side to the base side, and on the collector side, electrons are collected from the base side.




Bipolar junction transistors are classified into two types: NPN transistors and PNP transistors. The conduction process within the transistor involves both holes and electrons.

  • A low signal triggers the ON state for PNP, while NPN switches ON with a high signal. In PNP transistors, the P signifies the polarity of the emitter terminal, and N signifies the polarity of the base terminal.
  • In NPN, N denotes the negatively charged coating of the material, while P denotes the positively charged layer.
  • For PNP transistors, holes serve as the majority charge carriers, whereas in NPN transistors, electrons are the majority charge carriers.

It's important to note that the mobility of electrons surpasses the mobility of holes, making NPN transistors preferable for various applications.

These bipolar (BJT) components are referred to as current-controlled devices, in contrast to MOSFETs, recognized as voltage-controlled devices with terminals such as drain, source, and gate.


KSC1845 Pinout

The provided diagram illustrates the pin configuration of the KSC1845.


This device is equipped with three designated terminals:

  • Emitter: This serves as the input, allowing current to enter for amplification.
  • Collector: Positioned as the output, it facilitates the flow of amplified current outward.
  • Base: Functioning as the command center, it receives a small control current to activate the transistor.


These terminals are essential for external connections within the electronic circuit. They vary in size and doping concentration. The base side is lightly doped, the emitter side is highly doped, and the collector side is moderately doped. The collector side dissipates more energy due to its larger size than the other terminals. The substantial surface area of the collector side ensures effective heat dissipation.


Features of KSC1845


Enhanced Audio Frequency Low-Noise Amplification:

Tailored for audio frequency applications, the KSC1845 stands out as a specialized PNP transistor, excelling as a low-noise amplifier. Its unique characteristics make it an optimal choice for audio circuits, ensuring signal clarity and fidelity preservation.

Complementary Partner to KSA992:

In collaboration with the KSA992, the KSC1845 is the perfect complement, forming a meticulously matched pair that elevates the performance of amplification stages in audio equipment. This synergistic pairing guarantees balanced operation, especially in push-pull configurations.

Environmentally Friendly Design:

Embracing eco-conscious principles, the KSC1845 is crafted as a lead-free (Pb) device. This design choice aligns seamlessly with contemporary standards and regulations focused on reducing the environmental footprint of electronic components.

PNP Transistor Excellence:

As a member of the PNP-type bipolar junction transistor family, the KSC1845 facilitates current flow from emitter to collector when a positive voltage energizes its base terminal. This inherent design makes it versatile for a myriad of electronic applications.

Versatile Amplification:

Primed for signal amplification, especially in audio applications, the transistor proves its worth in preamplifiers, audio amplifiers, and circuits demanding signal reinforcement.

Switching Proficiency:

Beyond its amplification capabilities, the KSC1845 showcases remarkable switching capabilities, expanding its utility in electronic circuits that necessitate amplification and switching functions.


KSC1845 Specifications


Parameter Value
Type NPN BJT Transistor
Package TO-92
Voltage - Rated DC 120V
Number of Terminations 3
Max Power Dissipation 500mA
Current Rating 50mA
PC (Collector Power Dissipation) 350mW
hfe (DC Current Gain) 120 to 600
fT (Transition Frequency) 110MHz
Frequency Range Low to High Frequency
Noise Figure Low
Operating Temperature Range -55°C to 150°C
Storage Temperature Range -55°C to 150°C
Package Thermal Resistance (θJA) 200°C/W (approximate)


Thermal Characteristics



Electrical Characteristics



Absolute Maximum Ratings

  • Collector−Base Voltage: VCBO = 120V
  • Collector−Emitter Voltage: VCEO = 120V
  • Emitter−Base Voltage: VEBO = 5V
  • Collector Current: IC = 50mA
  • Base Current: IB = 10mA
  • Junction Temperature: TJ = 150°C
  • Storage Temperature: TSTG = −55 to 150°C


When utilizing this device, it is imperative to ensure that the operating conditions adhere to the specified ratings, as surpassing the absolute maximum ratings may damage the device. Additionally, prolonged exposure to these ratings beyond the recommended duration can adversely impact the device's reliability.

The collector current, denoted at 0.05A, signifies the load-bearing capacity of this device. It indicates the maximum current that the component can effectively support.

Power dissipation, quantified at 0.5W, reflects the amount of energy released during the operational phase of this component. It provides insights into the thermal considerations associated with the device.

With a current gain of 200, this device can amplify current. The current gain value highlights the extent to which the component can magnify input currents.

Specified at 120V, the collector-base and collector-emitter valves signify crucial parameters for proper device operation. Meanwhile, the emitter-base voltage at 5V indicates the voltage required to bias this component appropriately. Understanding and adhering to these specifications are essential for optimal performance and longevity of the device.


KSC1845 Equivalents/Replacements


The FJV1845 offers a comparable substitute for the KSC1845, sharing akin characteristics. Operating as a PNP transistor, it is applied in audio amplification and signal processing, adding flexibility to electronic circuit design.


A widely utilized NPN transistor, the 2SC1815 functions as a complement to the KSC1845. Together, they present a well-balanced combination for applications requiring PNP and NPN transistors, as seen in push-pull amplifier configurations.


An NPN transistor, the BC547, is an additional alternative that can be used with the KSC1845. While not a direct match, the BC547 finds applications in amplification and switching circuits, enhancing its adaptability in various electronic designs.


The 2N3904, a versatile NPN transistor, is commonly employed in amplification and switching applications. When appropriately paired in circuit designs, it can substitute for the KSC1845 in specific configurations, offering flexibility in component selection.


KSC1845 CAD Model



KSC1845 Working Principle

The base side serves as the primary region initiating transistor action. When a voltage is applied to the base terminal, it biases the device, causing current to flow from the collector to the emitter side.


KSC1845 structure

These bipolar devices lack symmetry. Exchanging the emitter and collector sides disrupts their functioning in the forward active region, shifting them into reverse active mode. The distinct doping concentrations of these terminals contribute to the absence of symmetry.


How to use KSC1845?

The primary region responsible for activating the transistor is the base side. Applying voltage to the base terminal biases the device, causing current to flow from the collector to the emitter. The schematic for KSC1845 is depicted as the structure figure in the last section.

Crucially, these bipolar devices lack symmetry. In other words, if the emitter and collector sides are interchanged, the terminals cease to operate in forward active mode and transition to reverse active mode.

The intentional loss of symmetry is achieved through the diverse doping concentrations of these terminals.


KSC1845 Application

High-Frequency Power Transformation:

Utilized in circuits demanding high-frequency power transformation, the KSC1845 contributes to effective signal processing in applications like RF (radio frequency) circuits.


Electronic Ballasts:

Integral to lighting systems, particularly electronic ballasts, the KSC1845 plays a pivotal role in regulating and managing current flow, ensuring optimal performance and energy efficiency.


Voltage Regulator Circuits:

Incorporated into voltage regulator circuits, the KSC1845 aids in maintaining a stable output voltage, which is crucial for the reliable operation of electronic devices.


Common Power Amplifier:

Deployed as a fundamental component in common power amplifiers, the KSC1845 assists in signal amplification, proving valuable in audio systems and other amplification applications.


Audio Amplification:

Applied in audio amplification circuits, the transistor elevates the quality and strength of audio signals, serving as a key element in audio amplifiers and related systems.


Signal Processing:

The KSC1845 finds application in signal processing scenarios where precise and controlled signal manipulation is imperative, ensuring accuracy in various electronic devices.


Bistable and Astable Multivibrators Circuit:

Integrated into oscillator circuits, the transistor generates oscillating signals crucial in electronic systems.


Switching Applications:

Suitable for switching applications, the KSC1845 facilitates the control of electronic signals and currents in different circuit sections.


Amplifier Configurations:

Frequently employed in various amplifier configurations, including single-stage and multi-stage amplifiers, to achieve the desired level of signal amplification.


Energy-Saving Lights:

Supporting energy-efficient lighting solutions, the transistor plays a role in the operation of energy-saving lights, making it integral to modern lighting technologies.


Supporting Loads Under 0.05A:

Specifically used in scenarios where the load current is below 0.05A, the KSC1845 is well-suited for applications requiring controlled and lower power consumption.


High Switching Power Supply:

Incorporated into high-switching power supply designs, the KSC1845 facilitates efficient power switching, making it suitable for various electronic devices and systems.


Voltage-Controlled Oscillators (VCOs):

In applications requiring VCOs, the KSC1845 may control the oscillation frequency based on voltage variations.


Low-Power Amplification:

The transistor suits low-power amplification requirements, proving valuable in battery-operated electronic devices.


KSC1845 Datasheet

Download KSC1845 Datasheet PDF.


KSC1845 vs KSC1845FTA

KSC1845 and KSC1845FTA are NPN transistors commonly used in electronics projects for amplification, switching, and various applications. Despite their similarities, notable distinctions exist:


Leakage Current: The KSC1845FTA exhibits a lower leakage current than the KSC1845. This implies reduced unwanted current flow through the transistor when turned off, offering advantages in circuits where stability and precision are paramount.

Gain (hFE) Range: The KSC1845FTA provides a slightly broader range of hFE values (current gain) than the KSC1845. This increased range enhances flexibility for circuit optimization, particularly when matching transistors for improved performance.

Package Marking: The KSC1845FTA often carries an "F" or "FTA" marking on its package, distinguishing it from the standard KSC1845.

Equivalents and Substitutes: In most scenarios, substituting the KSC1845FTA for the KSC1845 poses minimal issues. However, for projects demanding high precision or low leakage current, opting for the KSC1845FTA is advisable due to its enhanced specifications.


Choosing the Right Transistor

  • For general-purpose applications where leakage current and gain are not critical, the KSC1845 is a suitable choice.
  • For high-precision circuits or designs sensitive to leakage current, consider the KSC1845FTA for its improved specifications.
  • Always refer to the datasheets of both transistors to compare their specific electrical characteristics before deciding.








Both BJTs and JFETs exhibit distinct operational characteristics. BJTs operate as current-controlled devices, while JFETs are voltage-controlled, marking a fundamental contrast in functionality. Structurally, BJTs employ electron and hole charge carriers, whereas JFETs rely on only one type of charge carrier. Here are the key differences between BJT and JFET:


  1. The primary disparity lies in how output current is regulated. BJT operates with an output current controlled by the base current, whereas JFET relies on input voltage for current regulation.
  2. BJT typically features low to medium input impedance, whereas JFET is characterized by high input impedance.
  3. Applications requiring high gain and rapid response favor BJTs, while JFETs are more suitable for low-gain scenarios.
  4. BJTs exhibit low thermal stability, unlike JFETs, which showcase high thermal stability.
  5. Notably, BJTs are preferred in low-current applications, while JFETs are chosen for low-voltage applications.

Refer to 2N5457 JFET and J201 JFET for more information about JFET transistors.


Final Words

In summary, the KSC1845 NPN transistor stands out as a versatile and dependable component in electronics. Explored through its pinout, datasheet, equivalents, and diverse applications, the transistor proves its worth for amplification, switching, and various electronic projects. Its extensive usage is attributed to features such as a stable pinout configuration, detailed datasheet specifications, and compatibility with equivalent transistors. Whether utilized in common power amplifiers, regulator circuits, or low-power amplification applications, the KSC1845 showcases its adaptability and efficiency. As electronic enthusiasts and professionals navigate the complexities of transistor selection, the KSC1845 emerges as a reliable option, providing a blend of performance and versatility for various electronic endeavors.


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  • What is a KSC1845 transistor?

    KSC1845 is a bipolar junction transistor. The primary application of KSC1845 is in rapid switching and signal amplification.

  • How many layers is KSC1845 made up of?

    Three layers: A p-doped layer and two n-doped layers.

  • What does an NPN transistor do?

    The NPN transistor finds application in amplifying circuits, particularly in Darlington pair configurations, to enhance weak signals. It is utilized in scenarios where a current sink is necessary, and classic amplifier circuits like 'push-pull' amplifier circuits incorporate this component.

  • What are substitutes for the KSC1845?

    FJV1845, 2SC1815, BC547, and 2N3904.

  • Can I use the KSC1845 in a high-power application?

    The KSC1845 is unsuitable for high-power applications owing to its relatively low voltage and current ratings. It is advisable to consult the datasheet for the maximum ratings and ensure that your application adheres to these limitations. When dealing with high-power scenarios, contemplate employing a more resilient transistor.

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