TIP122 NPN Transistor

• The TIP122 is a Darlington pair NPN transistor. It functions like a normal NPN transistor, but since it has a Darlington pair inside it has a good collector current rating of about 5A and a gain of about 1000. It can also withstand about 100V across its collector- Emitter hence can be used to drive heavy loads. This increases the current gain and current rating of this transistor.
• Although TIP has high collector current and current gain, it is fairly simple to control the device since it has an Emitter-Base voltage (VBE) of only 5V and base current of only 120mA.
• The continues collector current of this transistor is 5A and our load consumes only 3A which is fine. The maximum base current is about 120mA, but I have used high value of 100ohm resistor to limit it to 42mA. You can use even a 1K resistor if your collector current requirement is less. The peak (pulse) current of this transistor is 8A so make sure your motor does not consume more than that.  This is just a model circuit diagram that shows the working on this transistor it cannot be used as such. So, similarly you can control your load in the same way.
• Alternative NPN Transistors: BC549, BC636, BC639,�BC547, 2N2369,�2N3055,�2N3904,�2N3906,�2SC5200
• TIP122 Equivalent Transistors:  TIP127 (PNP), 2N6045, 2N6532, 2SD1415, 2SD2495, BDT63, BDW2, KSB601, KSD560, MJF6388
• Same Family Transistors: TIP120, TIP121, TIP122 (NPN); TIP125, TIP126, TIP127 (PNP)

Applications

• Can be used to switch high current (upto 5A) loads
• Can be used as medium Power switches
• Used where high amplification is needed
• Speed control of Motors
• Inverter and other rectifier circuits