The BC548 is an NPN bipolar junction transistor.
BC548 is another general-purpose widely used transistor that can be easily accessed from reputable electronic components store, this transistor also has lots of good features on the basis of which it can be used in their electronic circuit, it can handle a maximum current of 500mA which is sufficient to drive many other components such as ICS, other transistors, circuit portions, relays, LEDs, etc. The max collector dissipation of the device is 625 milliWatt, which is another good feature to use as a small amplifier.
This blog gives you a basic overview of the BC548 transistor, including its pin descriptions, features, specifications, alternative products, etc., to help you quickly understand what BC548 is all about.
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Catalog
BC548 Pinout
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,
- lead 3 is the emitter.
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.
Pin Number
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Pin Name
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Description
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1
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Collector
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The flow of current will be through the collector terminal. It is dented by “C”
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2
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Base
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This pin controls the transistor biasing. It is denoted by “B”
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3
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Emitter
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The current supplies out through the emitter terminal It is denoted by “E”
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BC548 Advantage
BC548 NPN Transistor
BC548 is a NPN transistor so the collector and emitter will be left open (Reverse biased) when the base pin is held at the ground and will be closed (Forward biased) when a signal is provided to the base pin. BC548 has a gain value of 110 to 800, this value determines the amplification capacity of the transistor. The maximum amount of current that could flow through the Collector pin is 500mA, hence we cannot connect loads that consume more than 500mA using this transistor. To bias a transistor we have to supply current to the base pin, this current (IB) should be limited to 5mA.
When this transistor is fully biased, it can allow a maximum of 500mA to flow across the collector and emitter. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (VCE) or Base-Emitter (VBE) could be 200 and 900 mV respectively. When the base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region and the Base Emitter voltage could be around 660 mV.
BC548 Features and Specifications
Package Type: TO-92
Transistor Type: NPN
Max Collector Current(IC): 500mA (Continuous)
Max Collector-Emitter Voltage (VCE): 30V
Max Collector-Base Voltage (VCB): 30V
Max Emitter-Base Voltage (VEBO): 5V
Max Collector Dissipation (Pc): 625 miliWatt
Max Transition Frequency (fT): 150 MHz
Minimum & Maximum DC Current Gain (hFE): 110 – 800
Max Storage & Operating temperature Should Be: -55 to +150 Centigrade
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:
- 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)
BC548 Application
- Sensor Circuits
- Audio Preamplifiers
- Audio Amplifier Stages
- Switching Loads under 500mA
- Darlington Pairs
BC548 as Amplifier
A Transistors acts as an Amplifier when operating in Active Region. It can amplify power, voltage and current at different configurations.
Some of the configurations used in amplifier circuits are
- Common emitter amplifier
- Common collector amplifier
- Common base amplifier
Of the above types common emitter type is the popular and mostly used configuration. When used as an Amplifier the DC current gain of the Transistor can be calculated by using the below formulae
DC Current Gain = Collector Current (IC) / Base Current (IB)
BC548 as Switch
The region responsible for a transistor to work as a switch are Saturation Region and the Cut-off Region. When we apply a high enough current at the base of the transistor, it makes a path for the collector current to go through the base towards the emitter.
In order to use the transistor as a switch, it must be driven into the saturation region with enough base current. And a transistor operates as a closed switch under the saturation region.
Transistor as a closed switch
As soon as a positive signal (in form of voltage and current) is removed across the base of the transistor, the flow of electric current between the collector and emitter becomes zero. And the transistor behaves like an open switch under the cut-off region.
Transistor as an open switch
This simply implies if we apply signal (voltage/current) across the collector and emitter but not across the base, the transistor will not work. But a small signal across the base is enough to make it work.
BC548 Replacement and Equivalent
BC547, BC549, 2N2222, 2N3904, BC550 (Pin configuration of some transistors may be different from BC548, check pin configuration before using or replacing in a circuit)
BC548 Complementary Pairs
The PNP counterparts of the BC546 to BC550 are the BC556 to BC560 respectively, i.e. the type numbers are higher by ten.
BC558
The BC558 is the PNP version of the BC548 and has higher voltage versions: BC556 and BC557, and lower noise versions: BC559 and BC560.
BC548 Equivalent Transistors
BC549, BC636, BC639, 2N2222 TO-92. 2N2222 TO-18, 2N2369, 2N3055 , 2N3904, 2N3906 , 2SC5200
How to Safely Long Run BC548 in Circuit
To increase the durability and performance of this device the user much follow the guide lines and should not increase the values as described below. Do not drive the transistor above 30V, always make sure to place its pins right in the circuit, do not provide load more than 500mA, and always use a suitable resistor at the base of the transistor to provide it required current. Do not use or store the device in temperature above +150 centigrade and below -55 centigrade.
Where to Use BC548
BC548 transistor can be used in many general purpose applications; you can use it in the replacement of other general purpose transistors 2N3904, BC547, etc. as described above. A part from that it can be used as a switch to drive load under 500mA. The 500mA collector current is quite good feature for this size and type of transistor therefore you can drive wide variety of loads at the same time in an electronic circuit. Moreover, this transistor also has very good DC current gain and collector dissipation characteristics which makes it ideal to use in the amplification and pre-amplification stages of an electronic circuit.
Component Datasheet
BC548 Datasheet
FAQ
- What is BC548 Transistor?
BC548 is a NPN transistor so the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. BC548 has a gain value of 110 to 800, this value determines the amplification capacity of the transistor.
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- What is the Use of BC548 Transistor?
BC458 is a general-purpose NPN transistor used in many electronics projects and devices. BC548 transistor is used for amplifying and switching purposes in electrical circuits. Like every other NPN transistor, it consists of three pins: the collector, base, and emitter.
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- How a Transistor Works as a Switch?
By turning a small input current into a large output current, the transistor acts like an amplifier. But it also acts like a switch at the same time. When there is no current to the base, little or no current flows between the collector and the emitter. ... So the base current switches the whole transistor on and off.
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- What is the Difference Between BC547 And BC548?
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.
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- What is the max collector dissipation of the transistor BC548?
625 milliWatt
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- What type of package is the BC548 supplied in?
TO-92 3-pin
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- What is the gain value of BC548?
110 to 800
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