Two Motorola Transistors Became the Default NPNs
allaboutcircuits.com35 points by ChuckMcM 3 days ago
35 points by ChuckMcM 3 days ago
Just so long as we remember to check it'll fit the need. I recently inherited a design that used some parts from the 70s and they were not up to the task. Drop-out voltages too high, gate threshold voltages too high; whatever spec could be violated was. Just because it's been used for 50 years doesn't mean it's the right part for the job
In fact, unless ubiquity in availability is a really core part of the design requirement, they almost certainly aren't the right part for the job.
Most parts in most designs aren't anywhere close to being specification-critical. Specifying the 3904 is a great way to say "I need an NPN transistor here, and it doesn't really matter which one" (because, oh man, they can ship a lot of different things in that "3904" bin spec, and they do). So the "jellybeans" are often ideal choices.
When they are not, that is when the design engineer earns their pay.
The 2N3904 is an old friend who has never changed. I've been using him since the 80s and he's still my first choice whenever anything general-purposey comes along.
BC547? 337? I think they are Texas devices, much popular too.
Those were originally Philips devices, but like with the American JEDEC part names, after a device with an European part name, like BC337 was registered, any semiconductor device manufacturer could sell equivalent devices.
The European part numbers provided much more information than the American part numbers.
JEDEC 2Nxxxx just told you that this is some kind of transistor or thyristor, instead of being a diode like 1Nxxxx.
BC told you that this is a silicon small-power audio-frequency transistor.
There were separate codes for other materials and for many other kinds of transistors, diodes and thyristors (for example AD = germanium high-power audio-frequency transistor, BF/BL = Si low/high-power RF transistors, BS/BU = Si low/high-power switching transistors, BR/BT = Si low/high-power thyristors, BA/BY = Si low/high-power rectifiers, BB = Si varicaps, and many others).
Motorola and some other US companies, like Texas Instruments and Fairchild, entered the transistor market very early, when they defined types like 2N2222, which became industry standards.
However, because these devices were defined early, they had rather poor characteristics. When European companies like Philips, Siemens, Thomson, SGS-ATES entered the market later, they defined transistors and other devices with improved characteristics.
Because of this, in Europe the devices with European part numbers, like BC337, were generally preferred, because they provided better analog performance, e.g. lower noise and higher bandwidth.
However nowadays this has become mostly irrelevant, because a legacy transistor vendor makes only a small number of different kinds of transistors, distinguished mainly by die size, because bigger sizes are needed to handle bigger currents. Then the transistors are packaged and marked with any of the legacy part numbers, depending on what part number the customer orders.
So while old transistors may have quite different characteristics depending on the part name, many modern transistors behave the same, regardless how they are marked.
The naming system point is underrated; BC/BF/BU encoding actual device characteristics meant you could read intent from the part number alone. JEDEC 2Nxxxx tells you almost nothing without pulling the datasheet. A numbering system that requires external lookup to understand basic device class is a worse system regardless of how entrenched it gets.
> BC told you that this is a silicon small-power audio-frequency transistor.
BC breaks down as a silicon device, with no heater voltage, and a "triode".
If it was germanium, it would be AC <something>.
So BC548 is a silicon "triode", AC128 is a germanium "triode", and PC97 is a triode with a 300mA-rated heater (P is series connected with other valves, 300mA) in a B7G base (the 9).
"BF" might be an RF transistor although "F" was really used to mean a pentode in valves.
And those dual NPNs used in expo converters in synths might be accurately enough labeled as BCC548, similar to the ubiquitous ECC83 dual triode.
You also see this with diodes, were AA119 is a germanium small-signal diode, and BY127 is a silicon high(-ish) power rectifier diode, for example.
Exactly, I grew up playing with BC547 and BC337s (my father was an electronics engineer) and only later found 2N2222 and 2N3904. Those were almost entirely unheard of in India.
This is an interesting article on how open licensing can help ensure viability long after the original designer has left the game.
BC109 for ever!
Maybe in US. We had BC107-BC109 and BC177-BC179