I'm an electrical engineering student in college and am very confused about some things in electronics. I have a pretty good idea of how basic electronics components work but im have trouble with knowing how to choose a component for a particular application. For instance if I am to use a diode, capacitor, or transistor how do I choose which one to use? Is it a mathematical thing like ohms law using specifications and reference sheets to calculate the one you need or is it something more complex?
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closed as too broad by Joe Hass, Stephen Collings, Daniel Grillo, placeholder, Nick Alexeev♦ Mar 16 '14 at 18:18
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It is something that you will learn as you go through your schooling and it will continue into your career. It isn't something that can be easily explained in a few sentences.
Selecting circuit configurations and the component values that go into them is usually an interative process. You start with what you know, usually related to the external interfaces that a circuit needs to have, propose a general approach based on what the circuit needs to do and your prior experience, and then fill in the details as you go.
Just selecting the component values for a single-stage transistor amplifier is a fairly involved process — one that you will certainly go through at some point in your schooling. You will see how the selection of one part puts constraints on the possible values of the other parts. Sometimes this leads to impossible situations, and you need to back up and reevaluate previous selections. You will eventually develop an intuition about "ballpark" values for common configurations, which will minimize the number of retries required.
Just be patient, pay attention, and the pieces of the puzzle will start to fall into place for you.
Here is one way to deal with it which is good in the beginning. Choose as you say, using Ohm's law and the rest of the rules and laws and methods from a typical intro electronics textbook.
As you design, think in terms of generic or abstract parts as represented by the schematic symbols. After you have drawn a circuit that makes sense to you, narrow your choices. As you do the calculations for choosing values do you get crazy high or low resistors or caps? Will your transistor need to be high power or high voltage? Do you have an op-amp driving a motor directly? Check worse case power dissipation in each part. Do you need a 5 Watt resistor? High current traces? Do you find you need a hard to get voltage source?
At each step, do a review of how you can change other values (or assumptions) in the circuit in order to keep parts choices within reason. Review the goal of the circuit. To do something with very low power? Provide high current? Amplify a signal? Filter noise or pass a particular frequency? Each will force choices of physical components, their placement, and sizes, and costs. It is a very fluid process.
Take a look at the Sparkfun Open Hardware devices. You can see the schematics, layouts, and pictures of finished products. They are not great layouts but they pass the usability test. (Their revision rate of very simple boards should scare beginners. Just ignore it. Something to do with the number of dogs per square foot.)
Search for "Design Ideas" from Electronics Design. There are years and years worth of designs in which someone found a cool way to simplify a circuit or use a part in an unusual way. These are a great way to see how others have made choices in the physical implementation of their idea. So, jump in and start doing it. Remember, experience gained is directly proportional to the amount of equipment destroyed.
You don't say how far along in your program you are, but if you know how components work, that's a step in the right direction. I think you should change your goal slightly. Forget about knowing which component to chose for a specific application. Concentrate instead on being able to look at a circuit and understand what it does. I'm not saying know every single node voltage, but a general idea.
For example, "This circuit is a noninverting amplifier running single supply, chained in series with a second order Sallen-Key low pass filter, feeding an ADC." From there, you can say, "well, it's single supply and feeding an ADC", and know you're going to need a rail to rail op amp, ideally optimized for single supply.
A lot of electronics is having an idea of what technology is available and its capabilities. Using a top down design approach, you will compose a problem into blocks. Each block will break down to a few ICs. More often than not, the datasheet will provide some kind of guidance on component selction. For example, switching regulator will probably recommend several specific models of inductor, or give parameters that matter, and will probably say to use low ESR, ceramic output capacitors.
It's impossible to know every part on the market. Once you get to industry, sales and application engineers are your best friends when tackling a new problem in unfamiliar territory. I recently inherited a design that required a buck-boost regulator. I have little experience with switching regulators, so a quick email to my rep explaining my requirements got me a list of potential parts. I read though the datasheets, and went back to him with a few questions, and after a couple emails back and forth, a part was selected. With his assistance, I anticipate it will work first rev.
Finally, once you get to industry, find another engineer that has been in industry for 5 to 10 years as a mentor. Not only can this individual help you with design problems, but also building up a network of contacts. Also, if a rep is going to stop by, try to meet with them, if for no reason other than making the contact.