Having a vocabulary - even the whole dictionary - doesn't make you Shakespeare. If you want to write well, you also have to learn about grammar, and then how best to communicate different types of information, how to structure a novel or a play. A big part of that is learned by seeing how other writers have done it before you. Same thing with music - notes and rhythm aren't enough. You need to learn patterns and structure.

Could you do it yourself, on your own? Maybe. But you get farther so much faster by learning from those that have walked before us.

 

I've been trying to learn how to design my own electronic circuits for years; I start with enthusiasm, learn a lot of new stuff, try to design something, fail miserably, get frustrated, and abandon it... then start all over again a few years later -this must be something like my 4th or 5th attempt-.

I'm a quick learner and I thought it would be like learning everything else, like programming a computer; you learn the basics (what each thing does) and then you figure out how to put them together on your own. But this ain't happening with electronics; everything seems to be already invented, and instead of putting things together on your own initiative you have to learn the designs made by other people, and then re-use them to make anything remotely original.

Am I right; or this is just not for me?

Is there any way to learn how to design circuits?... not even complex circuits... just simple circuits. For example: if I'm to make a flip-flop or an oscillator, the only way this seems to happen is by looking at other people's designs first and then copy them -you must know the circuit beforehand, you don't come up with it-. Is anyone ever able to design this things without knowing what other people did?

Hi Adam.

Well, You can learn how to design circuits by going to the university and try to be an Electronics Engineer. The base of electronics is Mathematics, So
you must have a good insight in mathematics (and sometimes even in physics) to be able to properly design circuits.

But yet you can try the book "Practical Electronics for Inventors" by Paul Scherz as well. It shows you how to go ahead by its simple literature, and math. But if I was you. I tried to start by "Op-Amps". You know, the formulas behind the Op-amps are almost easy and somehow STRIGHT FORWARD. Op-Amps are able to implement the mathematics functions, be used as amplifiers (even power amplifiers!),be used as oscillators or even be used as a switch and so on and so forth. So you can design a lot of different circuits by them but yet you KNOW what you are doing.

 

Well, You can learn how to design circuits by going to the university and try to be an Electronics Engineer.

You are kidding right?

The LAST thing you will learn in your electronics engineer course is how to design circuits.

Edit: Is the video in your description you ?
If it is : You talk about how hands-on experience is a much more effective way of teaching electronics ... and I agree
But hands-on experience in an electronics engineering course is as common as an oasis full of Hot swedish babes with endless supplies of ice-cold mojitos and sun beds in the Sahara

 

You are kidding right?

The LAST thing you will learn in your electronics engineer course is how to design circuits.

You've got to be kidding!

 

You are kidding right?

The LAST thing you will learn in your electronics engineer course is how to design circuits.

Edit: Is the video in your description you ?
If it is : You talk about how hands-on experience is a much more effective way of teaching electronics ... and I agree
But hands-on experience in an electronics engineering course is as common as an oasis full of Hot swedish babes with endless supplies of ice-cold mojitos and sun beds in the Sahara

Hi Shagas,

Sorry I am not aware of the universtiy system in your country, But you know, I told that as an electronics engineer. In university you (have to) read not only Electronics but mathematics & physics which are the structure and the basis of electronics, By doing so you EXACTELY know what you are doing when you try to design a circuit. But anyway some times the main problem is that the university students do not bother themselves to study hard/proper, So in the later situation nobody expects such an student to be an electronics designer (even if he finally gets the certification!).

Those kinds of courses are very good and helpful for beginners/hobbyists or for those guys who want to have a better insight about electronics, But even those books never suggest to stick with them and/or avoid going to university. And of course you might be agreed with me about this fact that there is a BIG difference between a person who reads them before or along with going to university and a person who has got a zero knowledge in electronics and goes to university. Furthermore please do not forget this fact that those kinds of books are mainly written and published for the hobbyists who do not need to cover a lot of things like say FFT or wave equation...

 

The base of electronics is Mathematics, So
you must have a good insight in mathematics (and sometimes even in physics) to be able to properly design circuits.

Perhaps, but I view most design challenges as logic puzzles more than as mathematical puzzles. I solve the logic first, and then work out the math if those details matter.

 

Hi Adam.

Well, You can learn how to design circuits by going to the university and try to be an Electronics Engineer. The base of electronics is Mathematics, So
you must have a good insight in mathematics (and sometimes even in physics) to be able to properly design circuits.

But yet you can try the book "Practical Electronics for Inventors" by Paul Scherz as well. It shows you how to go ahead by its simple literature, and math. But if I was you. I tried to start by "Op-Amps". You know, the formulas behind the Op-amps are almost easy and somehow STRIGHT FORWARD. Op-Amps are able to implement the mathematics functions, be used as amplifiers (even power amplifiers!),be used as oscillators or even be used as a switch and so on and so forth. So you can design a lot of different circuits by them but yet you KNOW what you are doing.

If I go to university again I'll probably do physics this time.

Electronics is more like a hobby for me; I'm not planning on working in the field nor specializing in any electronics area. I already worked as an electronic engineer 10 years ago, but it wasn't servicing or designing equipment; just installing alarm systems.

I now realize that I was a bit naive thinking that electronics was simpler than it really is; I actually thought that just because I knew what a resistor, a capacitor and a transistor were I should be able to create any circuit I desired by simply combining them. So, it's not that my goal was to design circuits, it's that I felt useless at electronics because I couldn't come with any circuit designs. Now I know I'm not supposed to with my current knowledge, I'm supposed to study basic circuits to implement them in my projects instead of creating them.

 

I already worked as an electronic engineer 10 years ago, but it wasn't servicing or designing equipment; just installing alarm systems.

This is actually a big part of the problem -- we tend to water down the meaning of terms to point that they lack any meaning at all. I'm sorry, but someone that "just installs alarm systems" is in no way working as an electronic engineer. And that is in no way a put down -- most competent electronic design engineers would struggle a bit to install anything much beyond a basic alarm system and, while they could do it in due time, would spend a lot more time and effort getting a system working than I'm sure you did. You had specialized knowledge and skills that allowed you to efficiently perform a set of tasks and most electronics engineers lack much of that knowledge and skill set.

My point is that by calling everyone that does anything remotely related to electronics an "electronics engineer", it becomes impossible to talk in any meaningful way what an electronics engineer is or does.

For my own part, I would define an "engineer" (and not the type of "engineer" that is, strictly speaking, "one that operates engines", such as a locomotice engineer) as someone that uses extensive theoretical and practical knowledge and skills for the purpose of analyzing and designing systems to solve specific problems.

 

Now I know I'm not supposed to with my current knowledge, I'm supposed to study basic circuits to implement them in my projects instead of creating them.

Adam, congratulation! That's a pivotal concept/key which you have learnt now! A complicated circuit or a project is simply composed of several simpler STAGES (ie simple or almost simple circuits), most of the times the circuits which are behind of these stages are not ORIGINALLY designed by the designer himself! Let me give you an example Adam, as an electronics designer Suppose I am going to design a high power FM trasmmitter. I do not try to design EVERYTHING by myself, In this regard I know for instance that a "colpitts oscillator" does exist, So again as as a designer who has learnt in university how a colpitts oscillator does work and knows the formulas behinds it, I'll try to change/modify/trim it the ways I want to get a powerful stable transmitter which meets my requirements.
Furthermore there are a lot of other components in the world which have got a DATASHEET, and the datsheet tells you exactly what to do to have your proper target circuit, For instance you can look up for "LM3886" datasheet and see how good it tries to help you to design a power amplifier which meets your requirements.

Good luck

 

The datasheets are your friend. Remember, the manufacturer WANTS you to be successful in using THEIR part to solve YOUR problem. So not only do they contain detailed knowledge of what the part will -- and won't -- do, but most have reference designs for circuits that use that part to accomplish various things. Sometimes you can just use one of those designs as is, and other times you can study it a bit, figure out what it is doing and why (and sometimes the datasheet will have a section explaining it), and then work on adapting it to your ends.

 

This is actually a big part of the problem -- we tend to water down the meaning of terms to point that they lack any meaning at all. I'm sorry, but someone that "just installs alarm systems" is in no way working as an electronic engineer. And that is in no way a put down -- most competent electronic design engineers would struggle a bit to install anything much beyond a basic alarm system and, while they could do it in due time, would spend a lot more time and effort getting a system working than I'm sure you did. You had specialized knowledge and skills that allowed you to efficiently perform a set of tasks and most electronics engineers lack much of that knowledge and skill set.

My point is that by calling everyone that does anything remotely related to electronics an "electronics engineer", it becomes impossible to talk in any meaningful way what an electronics engineer is or does.

For my own part, I would define an "engineer" (and not the type of "engineer" that is, strictly speaking, "one that operates engines", such as a locomotice engineer) as someone that uses extensive theoretical and practical knowledge and skills for the purpose of analyzing and designing systems to solve specific problems.

Yes, we used to have a laugh every time the boss called us electronic engineers.

Only one of us was a qualified electronic engineer (apart from the boss); he installed with us most of the time, but also repaired faulty equipment and designed new alarms systems.

Adam, congratulation! That's a pivotal concept/key which you have learnt now! A complicated circuit or a project is simply composed of several simpler STAGES (ie simple or almost simple circuits), most of the times the circuits which are behind of these stages are not ORIGINALLY designed by the designer himself! Let me give you an example Adam, as an electronics designer Suppose I am going to design a high power FM trasmmitter. I do not try to design EVERYTHING by myself, In this regard I know for instance that a "colpitts oscillator" does exist, So again as as a designer who has learnt in university how a colpitts oscillator does work and knows the formulas behinds it, I'll try to change/modify/trim it the ways I want to get a powerful stable transmitter which meets my requirements.

It's a pity that the first electronics course I did was so short; I was really learning with that guy, and I think we were beginning to study basic circuits when the course ended. The last thing we did was to study the stabilization stage of a power supplies with Zener diodes.

Furthermore there are a lot of other components in the world which have got a DATASHEET, and the datsheet tells you exactly what to do to have your proper target circuit, For instance you can look up for "LM3886" datasheet and see how good it tries to help you to design a power amplifier which meets your requirements.

Good luck

For now I was just doing tests with the components I had at home, but it's good to know that I should have in mind that many components have specific uses, like amplifying audio.

By the way, there's something I don't understand about transistors: the hFE... when I test a transistor with my tester, it gives me a number that's supposed to be the hFE, which is supposed to be the current gain. However, when I use that same transistor in a test circuit and apply X milliamps to the base I don't get X time hFE through the collector emitter; I get a much lower amperage. So I'm wondering, am I misunderstanding what hFE means, or is the multimeter wrong or giving me the measure in other units?

 

The hFE or current gain of a transistor is not fixed. It is a function of voltage, current and mode of operation. You cannot go by the meter reading alone.

 

The hFE or current gain of a transistor is not fixed. It is a function of voltage, current and mode of operation. You cannot go by the meter reading alone.

So, what is the multimeter's hFE reading useful for? I mean, is that number the gain for a certain voltage/current, and is there any way of using that number to calculate the approximate gain at a certain voltage/current?

 

So, what is the multimeter's hFE reading useful for?

It's an indication that the transistor might be OK. A very low reading is a bad sign.

 

So, what is the multimeter's hFE reading useful for? I mean, is that number the gain for a certain voltage/current, and is there any way of using that number to calculate the approximate gain at a certain voltage/current?

In addition to what wayneh said, sometimes people want matched transistors. Since hFE varies a lot in manufacturing, one can't assume two transistors have equal hFE, so people can test them to find two from a batch that are the same.

Also, when using a transistor as a voltage amplifier, there is a method which essentially ignores hFE and sets the gain by a resistor ratio. That's one way to get a definite gain with a voltage amplifier.

 

Transistor datasheets also give hFE figures for different voltages; don't they? Can I trust these, taking into account the error margin? I mean, for example, if I need a transistor to give me 100mA when I apply 5mA to the base at 3v, can I just go to the datasheets and look for transistor with 20 hFE for that voltage?

I'm a bit confused at the moment on how to calculate which transistor to use, and how hFE fits in this calculation. I assume that the bigger the multimter's hFE, the bigger the gain I will get from a particular transistor; is this true?

 

Transistor datasheets also give hFE figures for different voltages; don't they? Can I trust these, taking into account the error margin? I mean, for example, if I need a transistor to give me 100mA when I apply 5mA to the base at 3v, can I just go to the datasheets and look for transistor with 20 hFE for that voltage?

I'm a bit confused at the moment on how to calculate which transistor to use, and how hFE fits in this calculation. I assume that the bigger the multimter's hFE, the bigger the gain I will get from a particular transistor; is this true?

This is one of the more common misconceptions that people have when working with transistors -- that they can count on the transistor acting as a well-defined current amplifier. Go look up a data sheet, say for the 2n3904, and you will see that the range is pretty big. Even at the primary operating point the minumum value is 100 and the maximum value is 300 -- and that's at one specific value for the collector emitter voltage.

Instead, what you should do is learn how to design circuits that are relatively insensitive to the actual value of hFE provided it is at least some minimum value (and perhaps also less than some maximum value). Of course, how you develop the ability to design such circuits is by learning how to analyze circuits that others have designed that have this trait and studying them to understand why they have this trait.

 

I mean, for example, if I need a transistor to give me 100mA

If you're looking to use the transistor as a current source, look into current mirrors.

 

Transistor datasheets also give hFE figures for different voltages; don't they? Can I trust these, taking into account the error margin? I mean, for example, if I need a transistor to give me 100mA when I apply 5mA to the base at 3v, can I just go to the datasheets and look for transistor with 20 hFE for that voltage?

I'm a bit confused at the moment on how to calculate which transistor to use, and how hFE fits in this calculation. I assume that the bigger the multimter's hFE, the bigger the gain I will get from a particular transistor; is this true?

As mentioned, the transistor hFE is a typical value for given conditions.

Usually you want to select a transistor with higher hFE than you need and set exact gain (if required) using other components.

Example:
If you are designing a common emitter amplifier. with a gain of 20 you would select a transistor with a worst-case hFE considerably higher than 20 (being conservative). Then use resistors to set the gain at 20, because resistors can easily be selected to be as accurate as needed.

EDIT: Do you understand that you can't apply 3 volts directly to the base of a transistor? - A current-limiting resistor.
is needed.

 

Yes, I see what you mean; just looked at the datasheet for a BC547 and it can go from a minimum of 110 to a maximum of 800. I also remember that in the course we used to calculate the current through the transistor with the resistors and not the hFE.

But I remember measuring that same BC547 with my multimeter the other day and it had an hFE of around 600; which is within the margins in the datasheet. But then I measured in a test circuit with just the transistor and a base resistor that the ratio between the current through the base and the current through the collector emitter was around 40. How can that be; isn't hFE supposed to be a minimum of 110, which was confirmed by the multimeter with around 600? Or am I wrong in thinking that hFE equals the ratio between base emitter current and collector emitter current?