2N2222

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2N2222A with Emitter, Base and Collector identified as "e" "b" "c" respectively.

The 2N2222, also known as the PN2222 and commonly 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.

1 Specifications
2 Other uses
- 2.1 Negative resistance
- 2.2 Diode reference
3 External links

Specifications

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

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Negative resistance

When biased backwards, and with no connection to the base, 2N2222A are rumored to have negative resistance avalanche properties^{[citation needed]}. Similar to a tunnel or lambda diode, perhaps useful for simple oscillator circuits. This would be an abuse of the component never intended by the manufacturer.

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! The 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.