2N2222

The 2N2222, often referred to as the 'quad two' transistor, is a small, common NPN BJT transistor used for general purpose low-power amplifying or switching applications. It is designed for low to medium current, low power, medium voltage, and can operate at moderately high speeds. It was originally made in the TO-18 metal can as shown in the picture, but is more commonly available now in the cheaper TO-92 packaging, where it is known as the PN2222 or P2N2222.

pecifications

It is a 1 amp, 50 volt, 300 milliwatt transistor capable of operating up to 100 MHz, with a beta of at least 100. It's used in a variety of analog amplification and switching applications.

It is available in a variety of small through-hole and surface mount packages including TO-92, SOT-23, and SOT-223.

2N2907 is a complementary (PNP) transistor for the 2N2222. The 2N3904 is an NPN transistor that can only switch one tenth the current of the 2N2222 but has otherwise similar characteristics.

Other uses

Negative resistance

When biased backwards, and with no connection to the base, certain batches 2N2222A may exhibit "negative resistance" avalanche propertiesFact|date=June 2008. This can potentially be useful as an ersatz replacement for tunnel or lambda diode (which can be hard for an experimenter to acquire) in non-critical experimental circuits such as oscillators. This behavior may not be exhibited by any given 2N2222A since it is a side effect of certain transistor physical architectures. The specifications call for certain measured behaviors and parameters; any architecture that results in a sufficient yield of compliant parts may be used whether or not its unspecified behaviors match other spec-equivalent parts. Other parts that exhibit this behavior are thyristors and neon lamps. Despite misunderstanding among some hobbyists, such behavior does not imply energy production or any violation of known physics. [http://www.circuit-fantasia.com/my_work/conferences/cs_2006/paper.htm]

Diode reference

If you are really short of a reference diode, the base-emitter breakdown voltage may be used to give a fairly stable low-current reference voltage (slightly better than a standard zener and a lot cheaper than a designed-for-purpose part). The 2N2222A gives a slightly higher zener breakdown voltage than a 2N2222 - see data sheet. WARNING - use of a transistor in this way is guaranteed to damage it! Its hfe value will rapidly degrade, until the device is useless as a transistor! There were several discussions about this effect in 'Wireless World' in the 1970s.The use suggested in the previous paragraph is likely to have the same result.

External links

* [http://www.eecs.harvard.edu/cs141/resources/2N2222.pdf Datasheet for Philips Semiconductor's 2N2222 (PDF)]
* [http://www.fairchildsemi.com/ds/PN/PN2222.pdf Datasheet for Fairchild Semiconductor's equivalent PN2222 (PDF)]