How electronic circuits are designed,   How they work? - Page 1
Forum section: electronics / beginners

author: VickySalunkhe
author_rank: Regular Contributor
timestamp: October 16, 2017, 10:15:03 am
content: Electronic circuits really fascinates me.I always ask and try to figure out how that small complex circuit does a complex taskBut still didn't found out in much more clean way always i get the results this is the circuit it can do this, that , but how? Is the question. How to to design it.How those n numbers of resistor, capacitor, transistors are arranged in a such a manner for completing a task.Like for say a BMS circuit.How does it prevent the battery from over charging or over discharging?Like how do the electronic components get to know how much voltage, current is flowing through a wire and then operate a task depending on that situation.How does a fast charging circuit work?How to create a charger that can charge a battery fast but safely without blowing it?Does answer to all this question comes with experience (yeah of course it would)But is there a way so we can start to explore and grab the knowledge how does it work and how can we make it work?Looking for someone who can guide me from where to start and how to......Your help will be really appreciated thanks ...

author: rstofer
author_rank: Super Contributor
timestamp: October 16, 2017, 01:54:18 pm
content: I'm not going to offer up a course in electronics engineering, that would take too long.Every complex circuit is composed of a multitude of much simpler circuits which are themselves composed of even simpler ideas. In the end, everything comes down to Ohm's Law. It is the first law taught in engineering school and it is the one that is used more often than all the other laws combined.You want to measure a current? Easy, measure the voltage drop across a resistor. What size resistor? Ohm's Law. How much power will be dissipated (every voltage drop produces heat if current is flowing)? Ohm's Power Law.In school, we start by discussing sources of electrical energy. Then we move on to simple circuits - the beginning of the discussion on Ohm's Law. Then the circuits get more complex and we start talking about the two Kirchoff's Laws (current and voltage). Once we get to this point, we can analyze almost any circuit mathematically although the math gets quite ugly for AC circuits. Vectors, phasors, phase angle, imaginary numbers, and so on. But it's still just math - use a computer.Later we get to devices other than simple resistors. We add in things like capacitors and inductors whose characteristics vary with frequency. Then we add in transistors and MOSFETs and we're just about done with discrete components.Now we move to integrated circuits, digital and analog. There's a fork at this point and I was always more interested in digital. The math for analog was just too ugly back in the '70s, slide rules, no calculators. Digital all the way! "Anybody can count to one!" -- Bob Widlar (VERY famous analog circuit designer)https://en.wikipedia.org/wiki/Bob_WidlarThere are a lot of tutorials on the Internet including Dave's channel. There is even an MIT tutorial series for those inclined to see how it is taught in the big leagues. Google for something like 'electric circuits tutorial videos'.Here's a series:https://learn.digilentinc.com/classroom/realanalog/Then it's a matter of 'copy and paste'. For hobbyists, almost everything they could possibly want to do has already been done. Just find it on Google and modify it to suit. Maybe try to analyze the circuit a bit before building it.There is a difference between hobby electronics and electronic engineering and that difference is math! Engineering is ALL math with some intuition thrown in. There are shortcuts and 'rules of thumb' but, by and large, engineering is math.

author: TimNJ
author_rank: Super Contributor
timestamp: October 16, 2017, 05:16:08 pm
content: As stated above,firstyou need to gain a fundamental understanding of how different circuit elements interact with each other. The fundamental circuit elements are voltage, current, and resistance. (Eventually you'll learn about capacitance and inductance which is vaguely like resistance except with a time/frequency dependence.) You will learn that more advanced devices (transistors, for example) can be modeled using current, voltage, resistance and capacitance.It's all about building layers of abstraction and being able to plunge down when necessary.Thinking about your battery monitoring example, the below image is the basic "charging profile" of a lithium battery. You might use a lithium ion charge controller chip as the basis of your design. Basically you want to charge the battery at a constant current (constant flow of electrons) until it reaches some voltage, and then "top off the voltage" slowly by continually applying a smaller and smaller current. How does the controller do this? Well, it will use acontrol loop with feedbackto maintain a constant current. The control loop will likely sense the voltage across acurrent sense resistorand will adjust itself so that the voltage across that resistor is always the same (constant). (A constant voltage across a resistor implies a constant current.) The controller will start reducing the current once the voltage reaches a certain threshold. It will likely use acomparator(to figure out whether or not that condition has been met) and avoltage reference(to set the threshold voltage).All the items in italics are basic building blocks that make up a more complicated circuit. You may wish to Google them to see what they're about it. The point is, a circuit might look daunting and complicated from the outside but you can always break them down into smaller and smaller functional pieces.

author: rstofer
author_rank: Super Contributor
timestamp: October 16, 2017, 05:50:00 pm
content: More often than not, the chip manufacturer will have Application Notes explaining how to use their chips.Here is one:http://cds.linear.com/docs/en/design-note/dn188f.pdfGoogle for 'li battery charging circuit design'Buried in the schematic above is a simple voltage divider. Look at the ground connection on pin 4. Then look at the internal 1.2V voltage source. It goes directly into the comparator negative input then it comes out on pin 6 where it goes into a two resistor voltage divider before delivering a reduced voltage to pin 2, the negative input to the op amp. That pin 2 voltage is around 44 mV if I didn't make a math error. I get this from the resistor voltage divider calculation. Notice that there is a small capacitor to help stabilize the voltage.https://learn.sparkfun.com/tutorials/voltage-dividersOr an online calculator:http://www.ohmslawcalculator.com/voltage-divider-calculatorR11 is the current sense resistor and there are a couple of other voltage dividers in the circuit.Ultimately, Q1 passes the charge current to the battery.The document goes through a complete description of the circuit.And that's how we learn this stuff. We take a simple idea like Ohm's Law and expand it to voltage dividers and then we can calculate voltages at various points in the circuit and determine how they change during charging. We add in a knowledge of op amps and comparators and pretty soon we can understand how the circuit does what it does.With a calculator and an App Note, you can learn a lot about electronics. The entire theory of operation is spelled out, it's just a matter of comprehending the material and doing some experiments.Remember what I said about Ohm's Law - the most commonly used Law in electronics. At some point, Kirchoff's Laws make understanding a lot easier.Here's Dave's Op Amp Fundamentals video:Here is the Khan Academy presentation:https://www.khanacademy.org/science/electrical-engineering/ee-amplifiers/ee-opamp/v/ee-opamp-introI like all of the Khan Academy presentations - particularly those on math but they have an Electrical Engineering series as well.