Why is the transistor BC547 so-named?

BC547 is a general purpose NPN Transistor (datasheet here) which us very popular among hobbyist and engineers alike. But why is it so named?

The naming or more specifically “numbering” of most transistors can follow any of the three systems:

1. Pro-Electron (European)

2. Joint Electron Device Engineering Council (JEDEC)

3. Japanese Industrial Standard (JIS)

BC547 is a name registered under the Pro-Electron numbering system.

The Pro Electron system is the European type designation and registration system for active components, such as electronic tubes and cathode ray tubes, semiconductors, liquid crystal displays, sensor devices, etc. providing concise and unambiguous type designations. The system provides integrity of the designations, and creates transparent and unique product identification, thus preventing confusion in the market place.
All Pro Electron type numbers consist of a prefix followed by a serial number. The prefix, generally two or three letters, clearly classifies the devices into categories with a sub-classification into classes, series or families. The next page summarizes the PRO ELECTRON numbering system. 

A few examples of devices registered under the Pro Electron system are:

BC557, BC857, BC847, CNY17-4, BFW11 & BPW34 are a few other devices registered under this system. Some of the Integrated Circuits registered under this numbering system are:

PCF1105WP	digital IC; PC family; operating temperature range -40 to +85 °C; serial number 1105; plastic leaded chip carrier.
GMB74LS00A-DC	digital IC; GM family; operating temperature range 0 to +70 °C; company number 74LS00A; ceramic DIL package.
TDA1000P	analog IC; operating temperature range non-standard; serial number 1000; plastic DIL package.

---

NOTE1:

Transistor Variants:

• BC547 : NPN Through hole (TO-92 Package)
• BC557 : PNP Through hole (TO-92 Package) Complimentary to BC547
  
  
• BC847 : NPN Surface Mount (SOT23 Package)
• BC857 : PNP Surface Mount (SOT23 Package) Complimentary to BC847

BC847 and BC857 are SMD versions of BC547 and BC557

Lower breakdown voltage versions (ending in 8):

• BC548 is a lower voltage version of BC547
• BC558 is a lower voltage version of BC557
  
  
• BC848 is a lower voltage version of BC847
• BC858 is a lower voltage version of BC857

Higher breakdown voltage versions (ending in 6):

• BC546 is a higher voltage version of BC547
• BC556 is a higher voltage version of BC557
  
  
• BC846 is a higher voltage version of BC847
• BC856 is a higher voltage version of BC857

Datasheets:

• BC546, BC547, BC548 NPN
• BC846, BC847, BC848 NPN SMD
• BC556, BC557, BC558 PNP
• BC856, BC857, BC858 PNP SMD

---

NOTE2:

If you are an undergraduate engineering student studying in India and looking to build a project using any of these components, you can procure them from any of the electronic components retail shops that are there in Lamington Road, Mumbai. One of these is: Visha Electronics

---

NOTE3:

Checkout this PDF (mirrors: link1 | link2 | link3) for a summary of the Pro-Electron numbering system.

The official booklet describing the complete Pro Electron System (15th edition 2008-01) can be obtained from: http://www.eeca.eu/index.php/pe_booklet/en/

Wikipedia article for Pro Electron is here.

---

NOTE4:

About the other two numbering systems:

JEDEC System (wiki)

The other commonly used numbering system which one comes across is the JEDEC numbering system. 2N2222, 1N4007 and 4N35 are devices registered under this system. The device number consists of a digit, followed by the letter “N” and a serial number. The first digit is one less than the total count of useful electrical connections. Hence transistors (3 useful connections: Emitter, Collector, Base or Gate, Drain, Source) have ‘2’ as their first digit and Diodes (2 useful connections: Anode and Cathode) have ‘1’ as their first digit.

4N and 5N are reserved for opto-couplers. 

The serial number consists of two or more digits assigned consecutively, starting with number 21 for each class of device (1N and 2N are two different classes of devices).

If present, a suffix could indicate various things. For example, a 2N2222A is an enhanced version of a 2N2222. It has higher gain, frequency, and voltage ratings. Please check the device datasheet for its significance.

Instead of 2N and so forth, some manufacturers use their own system of designations. Some common prefixes are:

MJ	Motorola power, metal case
MJE	Motorola power, plastic case
MPS	Motorola low power, plastic case
MRF	Motorola HF, VHF and microwave transistor
RCA	RCA device
TIP	Texas Instruments (TI) power transistor, plastic case
TIPL	TI planar power transistor
TIS	TI small signal transistor (plastic case)
ZT	Ferranti
ZTX	Ferranti

The JEDEC Standard JESD370B “Designation System for Semiconductor Devices” is available at:

www.jedec.org/download/search/JESD370b.pdf

Japanese Industrial Standard

The JIS standard was based earlier on a standard JIS C 7012-1966 which has now been discontinued. In its place the standard EIAJ-ED-4001-1993 published by JEITA is now being used.

Some popular parts registered under this system are 2SA1187, 2SB646 (both are transistors). The part numbers under this system consist of a number followed by two alphabets and then a serial number. The system is summarized in the table below:

1st Number designates the type of device		2 Letters		The following figures denote the device serial number
1	Diodes	SA	PNP HF transistor	Serial number of component yields no indication of function or specification. Since this is a serial number may provide insight into date. A suffix after the serial number indicates that the type is approved for use by various Japanese organisations
2	Bipolar transistors	SB	PNP AF transistor
3	FET devices	SC	NPN HF transistor
		SD	NPN AF transistor
		SE	Diodes
		SF	Thyristors
		SG	Gunn devices
		SH	UJT
		SJ	P-channel FET/MOSFET
		SK	N-channel FET/MOSFET
		SM	Triac
		SQ	LED
		SR	Rectifier
		SS	Signal diodes
		ST	Avalanche diodes
		SV	Varicaps
		SZ	Zener diodes