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BC548 transistor

The BC548 is a general-purpose NPN bipolar junction transistor commonly used in European and American electronic equipment. It is notably often the first type of bipolar transistor hobbyists encounter and is often featured in designs in hobby electronics magazines where a general-purpose transistor is required.[1][2][3] The BC548 is low in cost[4][3] and widely available.[5]

History and usage

[edit]

The BC548 is a part of a family of NPN and PNP epitaxial silicon transistors that originated with the metal-cased BC108 family of transistors. The BC548 is the modern plastic-packaged BC108;[6] the BC548 article at the Radiomuseum website[7] describes the BC548 as a successor to the BC238 and differing from the BC108 in only the shape of the package. Datasheets for the BC548 give specifications that are identical to, or exceed, those of the BC108, BC148 and BC238 predecessors. Thus the BC548 (or BC546 to 550) is a valid substitute in any circuit designed for the older BC108 (or BC148), which includes many Mullard and Philips published designs.[citation needed]

Pinout and specifications

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The BC548 is supplied in a standard TO-92 3-pin package. The assignment of transistor elements (b, c, e) to leads, i.e. the "pinout", uses the same convention used by some - but not all - other TO-92 devices. As viewed in the top-right image, going from left to right, the pinout is as follows:

  • lead 1 (left in diagram) is the collector,
  • lead 2 is the base, and
  • lead 3 is the emitter.[8]

Sometimes the middle pin is supplied bent to form a triangle of leads (as found in TO-18 case transistors and, for example, the ZTX108-L) to match the pinout of the BC108 more exactly.

The BC548 part number is assigned by Pro Electron, which allows many manufacturers to offer electrically and physically interchangeable parts under one identification. Devices registered to this Pro Electron number must have the following minimum performance characteristics:[9]

  • Breakdown voltage, collector-to-emitter with base open-circuit VCEO = 30 V (see below)
  • Rated continuous collector current IC = 100 mA (Fairchild's BC548 at one time had a higher rating)
  • Rated total power dissipation Ptotal = 500 mW (some manufacturers may specify 625 mW - see below)
  • Transition frequency (gain-bandwidth product) ft = 150 MHz minimum (300 MHz typical)

Variants

[edit]

The BC548 was released with, and often is found together in datasheets with, the BC547 (higher voltage) and BC549 (lower noise) devices, that correspond to the original BC107 and BC109 variants of the BC108. This group of NPN transistors share many specifications and characteristic curves, but differ in voltage ratings - the BC546 and BC547 are essentially the same as the BC548 but selected with higher breakdown voltages, while the BC549 is a low noise version, and the BC550 is both high-voltage and low-noise.[10] The BC556 to BC560 are the PNP counterparts of the BC546 to BC550, respectively. See the BC108 family for a table of these differences, and comparisons with predecessor types.

Some manufacturers specify their parts with higher ratings, for example the Fairchild 1997 datasheet (547ABC, Rev B) for the BC547, sourced from Process 10 gave 500mA as the maximum collector current, while their datasheets dated 2002 have dropped the current rating to the standard 100mA.[11] The power rating (in free air at 25 °C) is also subject to variation, from 500 mW to 625 mW; the latter now being the most common. There is lot of variation in the ft-transition maximum frequency from manufacturer to manufacturer.

Gain groups

[edit]

The type number of any of the devices in this "family" may be followed by a letter, "A" to "C", indicating devices that have been selected that fall within a narrow range of gain (hFE). The same letters are used for this purpose in several other European transistors, and is similar in principle to the "Yellow", "Blue" (and so on) gain groupings in Japanese transistors, but should not be confused with the "A" suffix used with some American (JEDEC) devices, such as the 2N2222A, to indicate a variety of differences or enhancements over the base type.

The BC548 is available in three different gain groups:.

  • "A" indicates low gain (110 to 220, typically 180) at 2 mA collector current,
  • "B" indicates medium gain (200 to 450)
  • "C" indicates high gain (420 to 800)

So a BC548 might have a current gain anywhere between 110 and 800, but the gain of a BC548A would be within the range of 110 to 220.

Notes: Some manufacturers place slightly different limits on the gain groups, for example the "B" group has been quoted as 220-475 in a Philips 1997 datasheet. The BC547 variant rarely is available in the "C" gain group, and the BC549 rarely in the "A" gain group.

Complementary pairs

[edit]

The PNP counterparts of the BC546 to BC550 are the BC556 to BC560 respectively, i.e. the type numbers are higher by ten.

BC558

[edit]

The BC558 is the PNP version of the BC548, and has higher voltage versions: BC556 and BC557, and lower noise versions: BC559 and BC560.

SMD versions of the BC546 to BC560

[edit]

The surface-mount package versions are the BC846 to BC850 (and PNP versions: BC856 to BC860).

See also

[edit]

References

[edit]

Further reading

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

BC548

View on Grokipedia
from Grokipedia
The BC548 is a general-purpose NPN epitaxial designed for low-power amplification and switching applications in electronic circuits. It operates with a maximum collector-emitter voltage of 30 V, a collector-base voltage of 30 V, and an emitter-base voltage of 5 V, supporting a continuous collector current up to 100 mA while dissipating up to 500 mW of power. The transistor is categorized into three subclasses—BC548A, BC548B, and BC548C—offering DC current gain (hFE) ranges of 110–220, 200–450, and 420–800, respectively, to suit varying amplification needs. With a current-gain bandwidth product (fT) of 300 MHz, it performs effectively in low- to medium-frequency and control tasks. Housed in a compact plastic package with three leads, the BC548 is widely utilized in , sensors, and hobbyist projects, and it pairs complementarily with PNP counterparts such as the BC556 through BC560 series.

Introduction

Description

The BC548 is a general-purpose NPN epitaxial planar designed primarily for amplification and switching applications in electronic circuits. In its NPN bipolar junction structure, the consists of three terminals—emitter, base, and collector—where a small input current at the base controls a proportionally larger current flow from the collector to the emitter, enabling effective current amplification. It is commonly housed in a plastic encapsulation, which facilitates through-hole mounting on circuit boards. Produced by manufacturers such as and Central Semiconductor as a standard discrete component, the BC548 enjoys popularity in hobbyist and educational projects owing to its low cost and ready availability.

Historical Development

The , part of the BC series developed by and in the mid-1960s, became available in plastic packaging by the early 1970s as part of the broader BC series of NPN bipolar junction designed for general-purpose applications. This device emerged as a direct successor to earlier metal-cased models such as the BC108, BC148, and BC238, which had been developed in the mid-1960s using the can package. By 1978, the BC548 was already recommended for new equipment designs, reflecting its rapid adoption in production environments. The development of the BC series, including the BC548, was driven by and to establish a standardized lineup of low-power transistors that could meet the growing demands of and industrial circuits across . These transistors replaced older germanium-based OC series devices from the and early , transitioning to more reliable technology while adhering to the Pro-Electron numbering system for consistent European specifications. The BC548 specifically addressed the need for versatile amplification and switching in low-voltage, low-current scenarios, building on the foundational designs of its metal predecessors. A key innovation in the BC548's evolution was the shift from the expensive metal enclosure to the economical plastic package, which reduced manufacturing costs and enabled high-volume production for both professional and amateur applications. This packaging change, which became widespread in the , improved accessibility for hobbyists and aligned with global trends toward compact, lightweight components. Under the Pro-Electron system, the BC548 is functionally similar to JEDEC-registered devices like the for many low-power uses, facilitating cross-regional compatibility in . Production of the BC548 has persisted uninterrupted into the , with multiple vendors maintaining active lines as of 2025, underscoring its enduring role as a staple general-purpose without any widespread discontinuations. Suppliers such as Diotec Semiconductor and KEC continue to offer it in the package, supporting ongoing demand in legacy and new electronic designs.

Physical Characteristics

Package and Pinout

The BC548 is encapsulated in a TO-92 package, consisting of a small cylindrical plastic body with three inline leads extending from one end, optimized for through-hole mounting on printed circuit boards. This package type provides mechanical protection and facilitates easy insertion into standard PCB holes. The standard pinout configuration, viewed with the flat side of the package facing the observer and the leads oriented downward, designates the left lead as the collector (C), the middle lead as the base (B), and the right lead as the emitter (E). This arrangement corresponds to pin 1 (collector), pin 2 (base), and pin 3 (emitter) in JEDEC TO-92 specifications. The leads are constructed from copper alloy, typically plated with tin for enhanced solderability and corrosion resistance. The flat side of the TO-92 body serves as the primary polarity marker, indicating the front face for accurate pin identification during assembly. Mounting the BC548 benefits from the package's lead spacing of 0.1 inches (2.54 mm) between adjacent leads, ensuring compatibility with breadboards, perfboards, and standard 0.1-inch grid PCBs. Some manufacturing variants include color bands on the body to denote specific gain groups or part types, aiding quick visual identification.

Dimensions and Materials

The BC548 transistor is encapsulated in a TO-92 plastic package, which provides mechanical protection and facilitates through-hole mounting. The package body measures 4.32 to 5.33 mm in length and 4.45 to 5.20 mm in , with leads extending to a minimum length of 12.70 mm and a diameter of 0.41 to 0.55 mm; lead spacing is 2.54 mm (0.1 inches) between adjacent leads. The overall weight of the transistor is approximately 0.2 grams. The body consists of flame-retardant epoxy resin molding compound rated UL94V-0 for flammability resistance. The active element is an NPN epitaxial die, interconnected via or aluminum bonding wires to the . The leads are formed from , typically plated with pure tin in modern variants. Environmental specifications include an operating range of -55°C to +150°C and a storage temperature range of -55°C to +150°C. Lead-free variants compliant with RoHS directives have been available since the early 2000s, featuring tin-plated leads to eliminate hazardous substances.

Electrical Specifications

Absolute Maximum Ratings

The absolute maximum ratings for the BC548 NPN define the DC and thermal limits beyond which permanent damage to the device may occur, ensuring safe operation within specified environmental conditions. These ratings are critical for circuit designers to prevent exceeding the transistor's structural integrity, particularly in applications involving switching or amplification. The maximum collector-emitter voltage (VCEO) is 30 V, representing the highest voltage the can withstand between the collector and emitter with the base open. The maximum collector-base voltage (VCBO) is 30 V with the emitter open, and the maximum emitter-base voltage (VEBO) is 5 V with the collector open. The continuous collector current (IC) is limited to 100 mA to avoid overheating and degradation of the junction. Total power dissipation (Ptot) is rated at 500 mW when the ambient temperature (TA) is 25°C, with above this temperature at 4 mW/°C to account for increased . The maximum (TJ) must not exceed 150°C to maintain device reliability. Additionally, the resistance from junction to ambient (RθJA) is 250°C/W in free air, providing a measure of heat dissipation capability without forced cooling.
ParameterSymbolMaximum ValueConditionsSource
Collector-Emitter VoltageVCEO30 VBase openON Semiconductor Datasheet
Collector-Base VoltageVCBO30 VEmitter openON Semiconductor Datasheet
Emitter-Base VoltageVEBO5 VCollector openON Semiconductor Datasheet
Collector Current (Continuous)IC100 mA-ON Semiconductor Datasheet
Total Power DissipationPtot500 mWTA = 25°C; derates 4 mW/°C above 25°CCentral Semiconductor via Mouser
Junction TemperatureTJ150°C-ON Semiconductor Datasheet
Thermal Resistance (Junction-to-Ambient)RθJA250°C/WFree airCentral Semiconductor via Mouser

Typical Characteristics

The BC548 NPN demonstrates a DC current gain, denoted as hFEh_{FE}, typically ranging from 110 to 800, measured under conditions of collector-emitter voltage VCE=5V_{CE} = 5 V and collector current IC=2I_C = 2 mA. This gain is calculated using the equation hFE=ICIBh_{FE} = \frac{I_C}{I_B}, where IBI_B is the base current, evaluated in the at the specified VCEV_{CE} and ICI_C to ensure consistent small-signal amplification performance. These values position the BC548 as a versatile general-purpose within its operational limits, distinct from absolute maximum ratings that define device stress thresholds. The transition frequency fTf_T, which indicates the frequency at which the current gain drops to , is typically 300 MHz for the BC548, assessed at VCE=5V_{CE} = 5 V, IC=10I_C = 10 mA, and test frequency f=100f = 100 MHz. This high fTf_T supports applications requiring moderate-speed switching and amplification up to VHF ranges. In saturation, the collector-emitter saturation voltage VCE(sat)V_{CE(sat)} reaches a maximum of 0.25 V at IC=10I_C = 10 mA and IB=0.5I_B = 0.5 mA, and 0.6 V at IC=100I_C = 100 mA and IB=5I_B = 5 mA, enabling efficient low-voltage drop operation in switching circuits. The base-emitter voltage VBEV_{BE} under forward bias is typically 0.6 to 0.7 V at , specifically around 0.66 V at VCE=5V_{CE} = 5 V and IC=2I_C = 2 mA, reflecting standard silicon junction behavior. The BC548 exhibits a noise figure of 2 to 10 dB at 1 kHz under conditions of VCE=5V_{CE} = 5 , IC=200I_C = 200 μA, source resistance RS=2R_S = 2 kΩ, and bandwidth 200 Hz, supporting its use in general audio-frequency amplification.

Gain hFE Groups

The BC548 NPN is categorized into three distinct hFE (DC current gain) groups—A, B, and C—to enable precise selection based on the required amplification or switching performance in electronic circuits. These groups are defined under standard test conditions of collector-emitter voltage (VCE) = 5 and collector current (IC) = 2 mA at 25°C, ensuring consistent across devices. Group A offers the lowest gain range of 110 to 220, making it suitable for applications like low-gain switching where minimal base current drive is needed to achieve saturation. Group B provides a medium range of 200 to 450, offering a balance for general-purpose amplification and moderate switching tasks. Group C delivers the highest gain of 420 to 800, ideal for high-gain amplification circuits requiring significant current multiplication with low input signals. The specific variant is indicated by a suffix in the , such as BC548A for , BC548B for group B, or BC548C for , which appears on the device marking and for easy identification during and assembly. Within each group, the hFE value is guaranteed to fall within the specified range, providing a tolerance that accounts for variations while maintaining reliability in . hFE measurements adhere to the conditions outlined in manufacturer datasheets, with the parameter typically decreasing as collector current increases beyond 2 mA due to the transistor's inherent characteristics, as illustrated in typical DC current gain versus collector current curves. This behavior influences circuit stability at higher operating currents, underscoring the importance of group selection for the intended load conditions.

Complementary PNP Transistors

The BC558 serves as the primary PNP complementary transistor to the BC548 NPN transistor, offering closely matched electrical characteristics for use in complementary circuit configurations. It features a collector-emitter voltage rating of -30 , a maximum collector current of -100 mA, and current gain (hFE) groupings A (110-220), B (200-450), and C (420-800) that align with those of the BC548 to ensure balanced performance. This pairing allows for direct substitution in designs requiring opposite polarity operation while maintaining comparable amplification and switching capabilities. Other PNP transistors in the BC55x series provide complementary options for specific requirements when paired with their NPN counterparts in the BC54x family. The BC556 complements the high-voltage BC546 with a VCEO of -65 V and hFE similar to the BC548's groups, suitable for applications needing extended voltage tolerance. The BC557 pairs with the BC547, offering a higher voltage rating of -45 V and -100 mA collector current for moderately elevated power needs. For low-noise applications, the BC559 and BC560 complement the BC549 and BC550, respectively, with optimized noise figures while retaining standard current and voltage specs akin to the BC548/BC558 pair. Pairing the BC548 with its PNP complement, such as the BC558, provides benefits like matched voltage, current, and gain characteristics, which promote balanced operation and minimize in push-pull configurations, particularly in audio output stages. These matched parameters ensure symmetric signal handling between the NPN and PNP devices, enhancing efficiency and linearity in amplification circuits. The BC558 and other BC55x PNP transistors share the identical TO-92 package and pinout layout with the BC548, with pin 1 as emitter, pin 2 as base, and pin 3 as collector; however, the polarity is reversed, requiring appropriate circuit adjustments for PNP operation. The BC548/BC558 pair is commonly employed in Class B designs due to their complementary nature and reliable matching for audio signal processing.

Surface-Mount Equivalents

The surface-mount equivalents of the BC548 NPN are the BC846, BC847, and BC848 series, housed in the compact SOT-23 package and designed for general-purpose amplification and switching in modern PCB layouts. These devices correspond directly to the hFE gain groups of the BC548, with BC846A/BC847A/BC848A offering hFE of 110–220, BC846B/BC847B/BC848B providing 200–450, and BC846C/BC847C/BC848C delivering 420–800 at specified test conditions. For PNP counterparts matching the BC558 series, the BC856, BC857, and BC858 transistors serve as SMD equivalents in the same SOT-23 package, maintaining complementary electrical performance for push-pull configurations. The BC856A/BC857A offer hFE of 125–250, BC856B/BC857B/BC858B provide 220–475, and BC857C delivers 420–800 (note: not all variants available in every group). The SOT-23 package measures 2.9 mm in length, 1.3 mm in width, and 1.0 mm in height for the body, facilitating high-density mounting on boards compared to the original through-hole form. These SMD variants replicate the core electrical specifications of their TO-92 predecessors, including a collector-emitter voltage rating of 45 V for NPN; for PNP, -65 V (BC856), -45 V (BC857), and -30 V (BC858); maximum collector current of 100 mA, and power dissipation up to 250 mW, while preserving the hFE grouping for consistent performance in low-power applications. In the 2020s, SOT-23 packaged transistors like the BC84x/BC85x series have seen widespread adoption in space-constrained electronics, including mobile devices and IoT modules, driven by the demand for and automated surface-mount assembly.

Applications and Usage

General Applications

The BC548 is widely employed in small-signal amplification applications, particularly in audio preamplifiers where its low noise characteristics and current gain (hFE) of 110 to 800 enable effective signal boosting without significant distortion. It is also suitable for RF stages in general-purpose radio circuits up to the VHF range, owing to its transition frequency (fT) of up to 300 MHz, for hobbyist and basic communication projects. In switching roles, the BC548 handles low-power loads efficiently, such as driving LEDs in indicator circuits or actuating small relays with currents up to 100 mA, leveraging its collector-emitter voltage rating of 30 V and low saturation voltage for reliable on-off operation. Its versatility extends to oscillator circuits, where it forms the core of simple transistor-based designs for generating stable signals in timing or tone-producing applications. For sensor interfacing, the BC548 serves as a to condition weak signals from devices like (utilizing its base-emitter junction as a for thermal sensing) or light-dependent resistors, ensuring compatibility with inputs or logic levels. Additionally, its ubiquity and low cost make it a staple in educational kits, where it introduces fundamental concepts of biasing, gain, and circuit behavior through straightforward experiments.

Circuit Examples

The BC548 is frequently employed in a common-emitter amplifier configuration using to achieve stable voltage gain for signal amplification tasks. A typical setup with a 9 V supply might use two base resistors (e.g., 47 kΩ and 22 kΩ) for to set quiescent Ic ≈ 1-2 mA, with a 1 kΩ , resulting in a voltage gain of approximately 40-100, suitable for audio preamplifiers or signal boosting. For switching applications, the BC548 operates effectively as a low-side switch driven by a GPIO pin to control loads like LEDs. A common circuit connects the base to a 3.3 V or 5 V GPIO through a 1 kΩ current-limiting , the collector to a 5 V supply via a 330 Ω and LED, and the emitter to ground; when the base is high, the saturates, illuminating the LED with up to 20 mA collector current. In pair configurations, two BC548 transistors are cascaded to multiply current gain (often exceeding 10,000), ideal for driving sensors or low-current relays from weak input signals. The first transistor's collector connects to the supply, its emitter to the second's base via a (e.g., 100 Ω), and the second's collector-emitter path handles the output load, enhancing sensitivity in applications like touch sensors. Safety considerations are essential when using the BC548. For inductive loads such as relays or motors, a (e.g., 1N4148) across the load prevents voltage spikes that could damage the . Additionally, derate power dissipation above 25°C at approximately 5 mW/°C (per manufacturer datasheets, with total dissipation typically 500 mW at 25°C) to avoid . Compared to the , the BC548 offers similar performance in general-purpose amplification and switching but has a lower voltage rating (30 V vs. 40 V) and is often preferred in European designs due to its Pro Electron numbering system, though both share comparable hFE ranges around 100-300.

References

  1. https://www.mouser.com/datasheet/2/149/BC547-190204.pdf
  2. https://www.onsemi.com/download/data-sheet/pdf/bc550-d.pdf
  3. https://www.electronics-tutorials.ws/transistor/tran_2.html
  4. https://www.mouser.com/datasheet/2/68/bc546-48abc-541436.pdf
  5. https://www.theengineeringprojects.com/2020/07/introduction-to-bc548.html
  6. https://frank.pocnet.net/other/Philips/elcoma/Philips_ReplacementGuideForSemiconductors_1978-10.pdf
  7. https://www.gracesguide.co.uk/Mullard
  8. https://www.mouser.ca/c/semiconductors/discrete-semiconductors/transistors/bipolar-transistors-bjt/?series=BC548
  9. https://www.taydaelectronics.com/bc548-transistor-npn-30v-0-1a.html
  10. https://www.digikey.com/htmldatasheets/production/2985488/0/0/1/to-92-case-package-details.html
  11. https://www.openhacks.com/uploadsproductos/bc548.pdf
  12. https://cdn-reichelt.de/documents/datenblatt/A100/BC546_48-CDIL.pdf
  13. https://www.torex-europe.com/download/clientfiles/files/Package%20info%201/TO92e_pkg.pdf
  14. https://resources.pcb.cadence.com/blog/2023-wire-bonding
  15. https://www.onsemi.com/download/data-sheet/pdf/bc556bta-d.pdf
  16. https://www.ic-components.com/blog/BC558-transistor-pin-configuration-and-datasheet-details.jsp
  17. https://assets.nexperia.com/documents/data-sheet/BC847X_SER.pdf
  18. https://assets.nexperia.com/documents/data-sheet/BC856_BC857_BC858.pdf
  19. https://www.nexperia.com/packages/SOT23.html
  20. https://www.businesswire.com/news/home/20230511005471/en/Global-Small-Outline-Transistor-SOT-Package-Markets-2021-2022-2023-2031-Miniaturization-of-Electronic-Devices-Advancements-in-Semiconductor-Packaging-Bolsters-Growth---ResearchAndMarkets.com
  21. https://www.watelectronics.com/bc548-transistor/
  22. https://www.utmel.com/components/bc548-npn-transistor-datasheet-equivalent-and-circuit?id=300
  23. https://www.etechnophiles.com/bc548-transistor-pinout-specifications-datasheet-and-applications/
  24. https://www.anypcba.com/blogs/electronic-component-knowledge/bc548-transistor-a-comprehensive-guide-to-its-applications-alternatives.html
  25. https://www.eleccircuit.com/transistor-crystal-oscillator-circuit-ideas/
  26. https://www.rgelectrics.com/bc548-transistor-pinout-features-equivalent-and-applications-explained-in-detail/
  27. https://www.next.gr/circuits/sensor/bc548-heat-sensor-diagram-circuit-c20271
  28. https://aichiplink.com/blog/BC548-Transistor-Pinout-Datasheet-Equivalent-and-Circuit_334
  29. https://electronicsclub.info/transistorcircuits.htm
  30. https://www.onsemi.com/pdf/datasheet/bc546-d.pdf
  31. https://www.kasuo.com/technical-articles/bc548-npn-transistor/
  32. https://www.utmel.com/components/what-is-the-difference-between-them-2n3904-vs-bc547?id=819
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