The BC548 is a general purpose epitaxial silicon NPN bipolar junction transistor found commonly in European electronic equipment, and part of an historically significant series of transistors that began in 1966 with Philips' introduction of the BC108 and its high-voltage BC107 and low-noise BC109 variants. The BC107/8/9 devices became the most used transistors in Australia and Europe, and subsequent members of the series in plastic packages (such as the BC547, BC548 and BC549) retained the specifications of the metal-cased BC107/8/9 essentially unchanged except for improvements - in thermal resistance and reliability for example.
The part number is assigned by Pro Electron, which allows many manufacturers to offer electrically and physically interchangeable parts under one identification. The BC548 is commonly available in European Union countries. It is often the first type of bipolar transistor young hobbyists encounter, and is often featured in circuit diagrams and designs published in hobby electronics magazines.
BC548 is one of a series of related transistors: BC546 to BC550. These have broadly similar ratings and the same collector current and hfe, but their breakdown voltage ratings VCEO and VCBO vary across the range. -548 has a 30 V VCBO, the -547 50 V and the -546 80 V. The -549 and -550 variants are low-noise versions.
The pinout for the TO-92 package used for the BC546 to BC560 has pin 1 (the leftmost pin in the diagram above, i.e. when the flat face of the package faces the viewer with leads at the bottom) attached to the collector, pin 2 connected to the base, and pin 3 connected to the emitter. Note that not all transistors with TO-92 cases follow this pinout arrangement.
Devices registered to this Pro Electron number must have minimum performance characteristics.
- Breakdown voltage, collector-to-emitter with base open-circuit VCEO = 30 V*
- Rated continuous collector current IC = 100 mA
- Rated total power dissipation Ptotal = 500 mW (some manufacturers may specify 625 mW**)
- Transition frequency (gain-bandwidth product) ft = 150 MHz minimum (300 MHz typical)
In the summer of 2013, the manufacturer's budgeted cost for the part is less than US $0.03 in lots of 1000.
Notes: * VCEO and VCBO breakdown voltage ratings both equal 30 for the BC548/9, but not always so for other family members; see table below for differences. ** The BC546-BC560 types from On Semiconductor are rated at 625 mW total power dissipation at 25 °C in free air (derated by 5 mW/degree from 25 °C to 150 °C); other manufacturers may have lower ratings, for example Philips/NXP specifies a 500 mW limit.
The maximum power in practice will depend on ventilation details and ambient temperature; small-signal transistors such as these would normally be used at much lower power dissiapations (and so junction temperatures much below the maximum allowed).
The related types in this family can be summarised in the following table...
|Case||Polarity||65 V Vcbo||45 V Vceo||20-30 V*||Low-Noise 20-30 V*||Low-Noise 50 V|
(c-b-e) 350 mW
(c-b-e) 500 mW**
* Devices in this column have at least a 20 V VCEO rating. The original BC108 and BC109 had only a 20 V rating for both VCEO and VCBO; Subsequent versions of the BCxx8 and BCxx9 up until the BC5x8/9 mostly had a 30 VCBO rating; check datasheets for exact breakdown voltage ratings.
The metal TO-18 cased BC107, BC108 and BC109 were the first transistors in this family, with only "Tentative Data" in the October 1966 Philips Semiconductor Handbook (Part 2) internally dated 4.4.1966. The PNP Complementary types were the BC177, BC178 and BC179. These were all 300 mW, 175 °C, 100 mA-rated types, but at least one manufacturer (Siemens) followed with a lower current rating (50 mA continuous) recommended for their high-gain BC109. Other manufacturers produced version of the BC107/8/9 transistors with their own naming system, such as ZTX107 to ZTX109 and PN108, often in plastic cases. Breakdown voltage ratings for the BC108 and BC109 were 20 volt for both VCEO and VCBO, but (apart from ZTX108/9) many manufacturers of plastic encapsulated alternatives raised at least the VCBO rating to the 30 volt now fond in the BC548.
An early plastic case version of the BC107-BC109 transistors, BC147 to BC149, used what Mullard/Philips termed "Lock-Fit" encapsulation, with short firm leads specially designed for automated circuit board assembly equipment. The PNP versions were BC157 to BC159. Power dissipation was somewhat lower, with some manufacturers specifying 220 mW, but other specifications were essentially the same or slightly better than the original BC107/8/9 and BC177/8/9.
The PNP counterparts of the BC546-550, the BC556 to BC560, have identical ratings and very similar characteristics overall to their NPN counterparts (earlier generations of PNP transistors would have slightly lower gains in each A/B/C range and a lower average overall than their NPN counterparts).
The Absolute Maximum Ratings VCEO and VCBO differ in most transistors (for example the BC547 has a 50 V VCBO rating but 45 V VCEO rating; the BC108, BC148 and BC168 have VCBO or VCES ratings of 30 V but only 20 VCEO), but are identical in the case of the BC548; both relate to the maximum safe voltage between collector and emitter, but the VCEO rating applies to the situation where the base is either open-circuit or fed from a relatively high resistance source - and so the more prudent choice for designers, while VCBO (sometimes written BVCBO or V(BR)CBO) apply only to voltage across the collector-base junction - and may be valid in circuits where the base is supplied with a voltage from a low-resistance path.
The noise figure of the BC548 and most BCxx6/7/8 devices is less than 10 dB and typically 2 dB at a collector current of 0.2 mA; the low-noise counterparts: BC549 and BC550 are specified to have a noise figure of less than 4 dB and typically 1.2 dB under the same conditions, while the low-noise PNP complements - BC559 and BC560 - have a slightly lower typically noise figure of 1.0 dB.
The type number of any of the devices in this "family" may be followed by a letter to indicate a narrow range of gain (hFE) spread (although it is not so common for a BCxx7 or BCxx8 part to be available with a "C" gain grouping).
- "A" indicates low gain (110 to 220 at 2 mA),
- "B" indicates medium gain (200 to 450)
- "C" indicates high gain (420 to 800)
So a BC547 might have a current gain anywhere from 110 to 800, but the gain of a BC547A would be within the range of 110 to 220.
- ""MiniWatt:" DIGEST". Vol 7 Number 2. Philips Australia. February 1968. Retrieved 17 March 2014.
- "BC546 through BC550".
- Motorola Small Signal Transistor Data Book (1984 ed.). pp. 2–97,8–3.
- World's Transistor Comparison Tables, Tech/ECA, 1993, ISBN 981-214-444-7
- "BC548 − NPN Epitaxial Silicon Transistor". Retrieved 28 June 2013.
- "BC168 Datasheet (PDF) - Micro Electronics". Retrieved 17 March 2014.