The BC549C is an NPN transistor belonging to a group of general-purpose NPN semiconductors consisting of BC547, BC548, and BC549. These transistors are utilised in audio frequency, and small signal directly coupled preamplifiers.
The general-purpose range of transistors is a good substitute for basic non-critical audio applications, as these transistors are similar and equivalents to each other.
These transistors are the direct modern equivalent replacements to the earlier BC107, BC108, and BC109. The most noticeable difference is in the packaging and pin configuration. The BC109 package was TO-18 / SOT18 metal canister, whilst the modern BC549 package is a TO-92 / SOT54 plastic material.
The pin configuration is very simple and is collector, base, emitter.
The image above shows the transistor symbol for an NPN component.
BC549B Vs BC549C
The BC549 series subdivides further into two groups B, and C. This suffix indicates the current gain.
With Vce at 5 V, and Ic at 10 µA, the current gain (hFE) for B is typically 150, whilst for C is 270.
With Vce at 5 V, and Ic at 2 mA, the current gain (hFE) for B is typically 290, whilst for C is 500.
With Vce at 5 V, and Ic at 100 mA, the current gain (hFE) for B is typically 200, whilst for C is 400.
As you can see from this, the largest current gain is available from group C that is why the BC549C is more commonly used.
The BC549 is an NPN transistor; however, it also has a complimentary PNP version, which is the BC559.
The complimentary version has identical characteristics except it is a PNP type. This is very useful for building symmetrical push-pull preamplifier stages.
Here is a typical audio amplifier circuit using biasing resistors, and an LT700 output transformer.
The Difference between BC548 and BC549
The BC548 and BC549 are almost identical NPN transistors. They both have an absolute maximum collector rating of 100 mA, and power dissipation of 500 mW.
Both transistors have a maximum collector-emitter rating of 30 V, and collector-base rating of 30 V.
The main difference is that BC549 is a special low-noise type and available in groups B and C only, whilst BC548 is more general-purpose type and available in all three groups A, B, and C.
Due to the similarities between a BC548 and BC549, they are interchangeable within many low voltage non-critical circuits, and therefore considered equivalents.
As early as 1979, Ferranti Semiconductors were manufacturing the ZTX107, ZTX108, and ZTX109 transistors which were a direct equivalent replacement for the Philips BC series. The ZTX series came in an E-Line (TO-92) package formed by injection moulding silicone plastic to provide a rugged encapsulation.
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