# circuit design

Discussion in 'General Electronics Chat' started by indianhits, Oct 8, 2009.

1. ### indianhits Thread Starter Active Member

Jul 25, 2009
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Now this question has been bugging me for years.so is it true that while designing a circuit(like finding values of resistors,capacitors etc)we keep on testing for the right values till we get the required value that we wanted by making use of multisim or do we use formula's to find the right value of resistors,capacitors etc.

2. ### steveb Senior Member

Jul 3, 2008
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Using trial-and-error is a poor way to design, and this method should only be used as a last resort, when no other methods are available. It is better to establish an intelligent design method based on theoretical equations and desired specifications.

3. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
In other words, learn where it is appropriate to use the math. I don't use any SPICE, but I'm one of the more prolific designers for this site.

A good cookbook helps too, that is, a library of circuits you can modify to fit the application. Most circuit can be used many different ways, it is only a matter of how you look at them.

4. ### hgmjr Moderator

Jan 28, 2005
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I rely heavily on the mathematics that underpin the circuits that I design. Through careful application of circuit analysis techniques that I have honed over my career, I am assured that the circuit will operate as expected under all condition it has been designed to withstand.

I find that through the application of mathematical theory, I gain insights into the circuit's operation that would not have been revealed had I relied soley on simulation software.

Some designers use circuit analysis and simulation software both as a way of checking their work.

hgmjr

Last edited: Oct 8, 2009
5. ### Audioguru New Member

Dec 20, 2007
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I learned electronics long before simulators were invented so I simply use arithmatic and datasheets to design circuits that work perfectly.

I always use "worst-case spec's" so that even weak but passing transistors work in the circuit perfectly.

6. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
Simulators come in handy on circuits where speed is important. Bipolar transistor storage time comes to mind. It is difficult to analyze (for me, anyway). Simulators may not be particularly accurate at predicting the magnitude of turn-off delay due to storage time, but you can at least get a qualitative look at it. The results are definitely better than assuming the delay due to storage time is zero, which is what you get if you assume a simple model on a paper analysis. Below is a simple example on an inverting switch, using a generic NPN model (no junction capacitance and no storage time), a 2N3904 (a general purpose transistor), and a 2N2369 (a high speed switch). The inexperienced circuit designer might not expect 2usec of turn-off delay, and therefore, without a simulator, might not realize the advantage of choosing a specialized transistor for the application.
I cut my teeth on high speed bjt transistor switching and analog circuit design before there were any user-friendly (compared to the original Spice) simulators, and I found out about things like storage time the hard way, on breadboards. I still like to use a simulator, especially on high speed circuits.

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7. ### indianhits Thread Starter Active Member

Jul 25, 2009
86
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ok thank you very much first of all for the answers really helped me.but one more question and this will be last

i am 18 years old and i am currently doing my 2nd year in electronics and communication engineering and i would like to know if you guys knew how to design a circuit when you were at this age because i feel like a loser and i am studying hard to master this subject but still don't know how to design a circuit like choosing optimum value for resistor or capacitor etc for a particular load

8. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Don't beat yourself up. At 18, I did not have access to a lot of the tools, the parts or the depth of understanding needed to do much in the way of design.

The one thing you have going for you is the Internet and Forums such as this.

Hang in there,
hgmjr

9. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
I was playing with transistors long before I understood them. I enjoyed my college electronics courses, they filled in a lot of the gaps.

10. ### steveb Senior Member

Jul 3, 2008
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A few years back, I read an article which discussed what age a person reaches their peak ability in various professions. The claim was that engineers reach their peak at a later age than most professionals (early thirties) because there is a necessary balance between creativity and experience. They also mentioned that engineers are productive to a very old age because of the importance of experience. Creativity does diminish with age, but not very fast if you keep your mind active daily.

Two years is not enough for you to feel like master - not even close. Keep working hard and you'll get there.

11. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
I have been designing circuits for 45 years, but when I was 18, I was a freshman in junior college. I didn't have an electronics class until my junior year. Even then the first year or two focused on analysis. Synthesis came later. Don't worry, it will come.

12. ### indianhits Thread Starter Active Member

Jul 25, 2009
86
0
thanks thanks thanks now i feel much better.thank you very much!!!