I am new in electrical transistors. My project is to make a 1 watt audio amplifier. Can anyone provide a best amplifier circuit using darlington pair and 2N3904 transistor. i searched google. So please dont refer anything from google.
See the circuit below.
It is capable of doing what you want with not a lot more than you specify. It uses
2 x 2N3904, which is apparently what you have available
One additional PNP transistor which could be substituted by a wide range of other ones.
2 x capacitors
2 x resistors
2 x diodes
to complete the circuit.
Whatever you do you can expect to use some extra passive parts, and 2 each of R, C & D are reasonably minimal, so it effectively costs you an extra PNP transistor.
If this circuit does not meet your needs you should say why in enough detail to allow people to understand your real need.
There are many excellent examples accessible via Google.
If you search on likely search terms and then look at pages returned you could learn much.
Using image search provides an excellent idea of what the pages are about .
If you look here you will find many links to amplifier pages and some will meet your need.
The demand to use a specific transistor type has no obvious point except perhaps that you already own one. This is not the best way to choose a part for an amplifier.
Mention of "a 2n3904" implies that you want to use only 1 transistor. This is notionally doable but unusual and unwise. Also power inefficient as the amplifier must use either Class A or Class D (switching) - very unusual in this context.
It would be an excellent idea to explain WHY you want only to use a specific part and whether you insist on only using one transistor and why.
2n3904 datasheet here. It is rated at 40 V but only 200 mA and only 600 mW dissipation It would have trouble pulling the skin off a rice pudding and would be nobody's ideal choice for a 1 transistor 1 Watt amplifier.
What you appear to be asking for is doable but not sensible. What you are asking for may be sensible but if so, you need to explain it more fully.
This circuit is closer to what you want and uses a 2N3904 and 2 other transistors.
[The circuit is fromClass AB Audio Amplifier.
which provides a brief but good comment on the subject.
If this circuit is not suitable you need to explain why in more detail.
Your restrictions seem arbitrary and silly. Why only use a single darlington pair made from two 2N3904 transistors? Actually that restriction makes it essentially impossible because you want 1 W out. The darlington will act as a single active element, which means efficient topologies are out of the question. You are going to end up with class A operation, so the active element will have to dissipate 1 W also, which is a bit much for a 2N3904.
Step back and explain what you are really trying to accomplish and leave out any restrictions that aren't truly necessary. Not all things are possible. With too many restrictions you get no result at all.
For example, if this is a learning exercise, you might ask how to make a audio amplifier to drive a small speaker using common off the shelf small signal transistors. That can be achieved, and will be easier if complementary NPN/PNP transistors can be used. I see no point in specifying a darlington configuration. Most designs probably wouldn't include one even if you said a bag of 2N4401/2N4403 and arbitrary resistors and capacitors are available.