How to choose the right coil type (inductor)?!

I think we are all familiar with such a commercial park inverter circuits as An example you could simply supply 12 volts to its inputs Connect the multimeter to its outputs and then use the given potentiometer to adjust in the output voltage to 5 volts therefore you could say that about converter is a DC to DC converter, which can step down voltages and Best of all, it can do that job with a high efficiency, which was around 79% in my example here If we now take a look at the simplified circuit diagram of such a converter then we can see that it only requires a switch like MOSFETs a diodes a coil and capacitor to billets That is why I also created one during a previous video of mine with the help of the lm2577 Switch IC from Texas Instruments. I used this ICEA because it combines a MOSFET switch with the required feedback control system and Thus building up the buck converter circuits only required for additional passive components For mere leak oil selection was the hardest part though because there exists 100 micron recoils with different shapes sizes and with different core materials and I was never 100% sure which coil would be the best for the job To solve this problem the brought electronic ISOs group sent me a buck converter learning kits Which utilizes different kinds of coils? So in this video, we will not only find out how to calculate the inductance for such a buck converter But we will also find out how for example the size core material and temperature influence our utilized coils Let's get started This video is sponsored by the broad electronic Isis group Before supplying the learning kit board with current We have to figure out what kind of function D coil fulfills in the buck converter circuits To do that we firstly hook up 12 volts to our simplified super diagram and close the switch now Current flows from our voltage source through the coil through the loads and back to the source But as soon as current started flowing through the coil it simultaneously built up a magnetic fields Which in turn induced a voltage into the coil itself and thus created an opposing current Which is the reason why the original current through the coil can only rise slowly? While the current is now slowly rising in a relatively linear fashion The voltage across the coil is corresponding to this equation Pretty much constant and also opposites in comparison to the input voltage That means the output voltage equals the input voltage reduced by the voltage across the coil which therefore means that we successfully step down the voltage at the outputs of Course, we cannot keep the switch closed forever Because the stored energy of the coil in the form of the magnetic fields will at some point reach its maximum This state is called magnetic saturation in which a constant current flows that is only limited by the resistance of the windings of the coil if We neglect the load resistance or rather nearly short. It's there also does no longer exist a noticeable voltage across the coil and thus the output voltage does more or less equal the input voltage to Get the desired output voltage though. We have to open the switch at the right time Which would lead to an abrupt breakdown of the current if there wouldn't exist the inductive properties of the coil So during that switch opening moment The coil uses its stored energy in order to push a current through the loads and the diodes Which once again leads to relatively linear this and decrease of the current value? because of this current we got a voltage across the coil with reverse polarity in comparison to before Which reduce by the diode voltage? equals in the output voltage Now the current through the coil drops longer or shorter Before the switch gets once again closed depending on how much energy is required at the outputs and Because of the continuous repeating of the to switch States we create such a square wave signal for the switch The proportion between the on time of the switch and the cycle duration equals the so called duty cycle and The outer ring of the duty cycle depending on the output currents is called pulse width modulation Which can reach a maximum of 1 so 100% The higher this value becomes the more energy is being stored in the coil and Also, the output voltage gets closer to the input voltage. I Think due to this explanation of the functional principle of a buck converter it should be clear that the inductance value depends on a whole lots of different factors like the input voltage the occurring Resistances the load current the output voltage the duty cycle the switch frequency and even the ripple current So you can either use this relatively precise formula to calculate the inductance value Or make your life easier by simply following the recommendation of the ICS datasheets At this point some of you might think well I will just use a big inductance because it can store more energy and thus the converter should be able to output more power and When we have a look at different commercial buck converters, then it seems like this FIRREA is somehow corrects But in order to learn more about how to properly select a coil, let's have a look at the learning kit boards Which uses three different coils for its first our converter circuits? One of them features an inductance of 100 micro Andrea and two of them an inductance of 68. Micro Henry So after hooking up 12 volt power to the boards and connecting a constant load circuits to its outputs I had a look at the voltage and current wave of each coil on the oscilloscope and Even though the 100 micro Henry coil should be able to store the most energy I did not like its current flow with an output current above 1.2 m/s in comparison to the current flow of the second coil The reason for that is that the 100 micro NB coil uses ferrite as a core material while the second coil uses ayran powder The consequence is that the inductance of the first coil will drastically decrease at a certain DC current value Because the material reaches its magnetic saturation region While the inductance of the second coil will only decrease relatively constant across a wider current range Therefore you can see that at a similar coil size the choice of the core material can be more important than the actual Inductance value and you should always have a look at the magnetic saturation current and not exceeded With that being said we can move on to the second our converter circuits which coincidentally Uses a pig and a small coil with the exact same inductance value of 10. Micro Henry Both of them fulfill the job in the back when brooder circuits without a problem But it is not a surprise that the physical smaller coil starts causing problems at higher output currents before the bigger coil does One of the reasons is that the smaller coil reaches its magnetic saturation earlier and thus its inductance gets decreased But more important in this case, is that the temperature of the small coil? Increases up to 80 degrees Celsius and a current flow of 4 ms While the bigger coil would need 13 amps to reach the same temperature The reason is simple in order to achieve a certain inductance value. You need a certain number of windings this number is of course bigger for smaller coil in comparison to a bigger coil boots with the same core material and To achieve this number of windings for the smaller coil. We also have to use a wave in our enamel copper wire Well, the bigger coil can use a thicker wire Practically speaking that means that our smaller coil features an almost nine times bigger resistance in comparison to the bigger coil and Thus it produces nine times more power losses which need to get dissipated as heat But because the smaller coil also features less surface area to dissipate the heats we can easily slip into a region in which the winding isolation can melts and thus destroy the coil of Course, there are also other factors which influence the coil selection and if you're interested in learning more about them Then I would highly recommend checking out the experiment book that came with the learning hits Which tells you pretty much everything you need to know about coils Another assistance tool to select the right coil would be the red expert tool Which can conduct the simulation of different inductances in a circuits but nevertheless I hope that I was able to give you a small insight into the world of coils and That you now understand that the inductance value is not the only important property there is for example also the coil resistance and the magnetic saturation current and most of the time a small look into the datasheet of a coil can be very helpful of course, you can also visit the broad electronic Isis group websites to get more information about coils or to Order them since they come with very detailed data sheets Which for example eBay sellers do not offer in 99% of the cases? As always thanks for watching. Don't forget to Like share subscribe and hitting the notification bell Stay creative and I will see you next time

Channel: GreatScott!

Views: 236,348

Keywords: coil, inductor, inductance, calculate, converter, buck, boost, flyback, smd, smt, tutorial, guide, diy, project, beginner, beginners, energy, save, function, henry, uH, temperature, size, package, core, material, ferrite, iron, powder, winding, wire, copper, big, small, choice, choose, tip, würth, elektronik, red, expert, experiment, magnetic, field, mf, current, voltage, curve, oscilloscope, load, duty, cycle, frequency, clock, rate, ripple, greatscott, electronic

Id: hYOtx_2hYTU

Length: 11min 14sec (674 seconds)

Published: Sun Feb 23 2020