Want to make Darlington transistor(HELP)

[Zammi]

Hello, in my circuit there is a requirement of tip 122 which is npn darlington transistor. So instead of buying the component i decided to build my own darlington transistor. Can somebody provide me a detailed circuit diagram with resistors value given and individual transistor model no which i should use. I googled but could not find detailed circuit diagram.

Note- i have 2 bd139 transistor in stock

[pebe]

TheTIP122 has a maximum current rating of 5A, but a BD139 has a maximum current of only 1.5A.

If your circuit takes less than 1.5A then you can wire a BD139 as part of a darlington pair. If you google for 'wiki darlington pair' it will show how to wire it up. The BD139 would be the main transistor, and the one with its emitter feeding into the base of the BD139 should be a medium power NPN such as a 2N3904.

[Zammi]

circuit needs more than 1.5 amps. what transistors should i use for darlington pair?

[Zammi]

i am simultaneously bulding one more circuit that will be fed by darlington pair but its requirement is 0.15 Amps. It is a 12v dc fan. so will it fry at 1.5A.

[pebe]

The main transistor for a Darlington pair could be a TIP31 that would give you 3A, or a TIP35 that would give you 25A.
Alternatively, you could use a BD679 Darlington transistor on its own that would give you 4A and cost less than either of the other two.