how??

[kate]

im designing a circuit and wishes to realize it . how to choose the right component?

 

[Nigel Goodwin]

im designing a circuit and wishes to realize it . how to choose the right component?

By knowing what the component has to do! - your question is too vague for any explicit answer.

 

[kate]

what i mean is, for instance, there are many models of transistors right? which is which?

 

[Nigel Goodwin]

what i mean is, for instance, there are many models of transistors right? which is which?

You pick one to match the specifications you require, or (more likely) pick one you happen to have that matches your requirements. If you need specs on transistors I would recommend buying 'Towers International Transistor Selector', which is probably the definative work.

 

[Optikon]

what i mean is, for instance, there are many models of transistors right? which is which?

Make a drawing of your schematic & post it. Members on here can help you choose parts.

 

[gerenis]

kate r u kidding or it's for real?
If it's a general question, well, it takes attending a university on electrical engineering for 5 years, and you will know the answer partially.
Then a few year's designer experience could still back it up to come into fuller understanding...
So if you're in the first semester, or not even a student, it's still too early to ask such questions.

 

[Optikon]

kate r u kidding or it's for real?
If it's a general question, well, it takes attending a university on electrical engineering for 5 years, and you will know the answer partially.
Then a few year's designer experience could still back it up to come into fuller understanding...
So if you're in the first semester, or not even a student, it's still too early to ask such questions.

I think Kate has gone off to do other things...

But, I disagree, it's never too early to ask... maybe too early to understand! but I don't think that applies in this case though..

 

[gerenis]

I sure think all questions are welcome by members here.
I am just afraid there is no answer for that general a question that would fit within the limitations of forum posts.

 

[audioguru]

kate r u kidding or it's for real?
If it's a general question, well, it takes attending a university on electrical engineering for 5 years, and you will know the answer partially.
Then a few year's designer experience could still back it up to come into fuller understanding...
So if you're in the first semester, or not even a student, it's still too early to ask such questions.

Since when and why does it take so many years to learn how a simple transistor circuit works and how to design a circuit, how to read transistors' ratings then select one???

A 2N3904 or BC548 as an NPN, or 2N3906 or BC578 as a PNP will work in about 85% of transistor circuits and a 2N3055 or MJ2955 power transistor will work in most of the remainder. Designing a simple circuit for a FET or Mosfet transistor will take only a few more minutes of study.

I wish Google and the internet in general were around when I went to school. Then I could have learned stuff much quicker at my own rate. :lol:

 

[gerenis]

Hi audioguru,

Since when and why does it take so many years to learn how a simple transistor circuit works...

Please recall, the original question was absolutely theoretical about selecting components for designing a circuit, not just selecting transistors. I cannot find any trace of a "simple transistor circuit" in the original question. Transistors were brought up later just "for instance".

A 2N3904 or BC548 as an NPN, or 2N3906 or BC578 as a PNP will work in about 85% of transistor circuits and a 2N3055 or MJ2955 power transistor will work in most of the remainder. Designing a simple circuit for a FET or Mosfet transistor will take only a few more minutes of study.

Now, somebody should really talk to those stupid component manufacturers, too. They just do not stop investing in the production of hundreds if not thousands of different transistor types.

Indeed, even selecting a transistor can get tough...

What if Kate had the following problem (audio example to favor audioguru):

In the large signal voltage amplifier stage of a discrete transistor class AB audio amplifier, I want to know which transistor types are likely to send the whole circuit into oscillation and which are not.
Suppose you already have the whole schematic of the amplifier! The hard part is all done! It's just the type of one transistor missing. How simple the question: Will the amplifier work fine or oscillate with different transistor types in that position? Alas, no sample of the amplifier, no transistor samples either for tweaking (just data sheets in piles), so you need to solve it all in theory and come up with the results for Kate. What if she can't get a sleep until she knows for sure!
Open loop characteristics, loop gain, closed loop characteristics, Miller capacitance, pole-zero image, phase margin, Bode-plots, which stage determines the second pole frequency and to where is it shifted ...
The clock's ticking. Would you go explain it in a few minutes for someone without electronics education?

Hey, when selecting a transistor is so easy, why am I wasting my time. I better quit this forum and never return.

Happy Cristmas for all

 

[audioguru]

Well, if Kate likes smoke, she can use a little 2N3904 instead of a big 2N3055. That should be obvious to a noobie.

Hee, hee. :lol: There is a 30V/3A variable power supply project on another site. It was designed with a little 2N2219 video transistor as a power driver stage. The tiny transistor gets white hot internally, but only red hot on its case! It is in a TO-5 metal case so it burns without any smoke. :lol:

 

[Edigate]

Hello All,
I think we should stop discussing Kate's post. Kate probably cant remember she posted such a question. Lets wait for her next post.

 

[audioguru]

I think we should stop discussing Kate's post. Kate probably cant remember she posted such a question. Lets wait for her next post.

You know about her next question: "Why do all my LEDs burn out?"