PN2222 (2N2222) is the most common NPN bipolar junction transistor available in the market, hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin. 2N2222 has a gain value of 110 to 800, this value determines the amplification capacity of the transistor. The maximum amount of current that could flow through the Collector pin is 800mA, hence we cannot connect loads that consume more than 600mA using this transistor. To bias a transistor we have to supply current to base pin, this current (IB) should be limited to 5mA.
When this transistor is fully biased then it can allow a maximum of 600mA to flow across the collector and emitter. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (VCE) or Base-Emitter (VBE) could be 200 and 900 mV respectively. When base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region and the Base Emitter voltage could be around 660 mV.
How to Safely Long Run in a Circuit
To get good and long term performance from this transistor it is suggested to not drive loads more than 100mA, always use a suitable base resistor, do not provide collector-emitter voltage more than 40V and always operate or store in temperatures above -55 centigrade and below +150 centigrade.