Inductor selection

Discussion in 'General Electronics Chat' started by xw0927, Jan 4, 2011.

  1. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    Hey dude,

    I am really frustrated with the inductor selection.

    I don't understand inductor well at all.

    I need to buy an inductor which got to be inserted into my boost converter.

    My switching frequency is around 20kHz and input voltage source is a battery with 12V and 1.2A.

    Problem is that I don't know what type of inductor is suitable. The inductor is supposed to be more than 1.3mH (from the calculation)

    After browsing some online-buying website, I found that inductor with larger value will have lower maximum DC current. Is that true?

    Or should I make the inductor myself? But, I have no ideas about it at all. :(

    If any experts at power-e please help me~~

    Thanks in advanced.
     
  2. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    xw0927 likes this.
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    By the way. A 1.3mH high current inductor is quite big. And it will not be easy to find it. Perhaps you can do something else that will require a smaller inductor. Do you have more info like a schematics of your design?
     
  4. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    i do have the schematic, 1.3mH is the value from calculation. However, when i was using software to generate this circuit. Even the inductor value is lower than that, it can give me the required output as well...

    Sigh...

    http://forum.allaboutcircuits.com/attachment.php?attachmentid=25755&d=1293090894

    this is the schematic...
     
  5. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    hey, i hv to do some correction...
    the current wasn't 1.2A...=.=''
    it is just a 1.2Ah battery...
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Have a look at Ronald Dekker's page:
    http://dos4ever.com/flyback/flyback.html

    You're using basically the same schematic as his boost converter.
    He explains inductors very nicely, and shows you how to make your own and test them.
     
    absf likes this.
  7. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    But, my instructor wants me to use (if can) commercial inductor/transformer in this circuit instead of making the inductor myself. That is the problem.. haiz..
     
  8. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    Specifications

    Inductance 100μH Lead Pitch 29.3mm Maximum DC Current 7.8A Maximum DC Resistance 40mΩ Maximum Operating Temperature 85°C Maximum Self Resonant Frequency 3.3MHz Minimum Operating Temperature -40°C Minimum Quality Factor 34 Product Depth 29.8mm Product Height 21.8mm Product Length 32.4mm Test Frequency 1kHz Tolerance 10% Type General Purpose



    i wish to ask if the specification of an inductor is written as above.

    What is the meaning of Test frequency ???
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    How did you arrive at 1.3mH for the required inductance?

    Show your work.
     
    xw0927 likes this.
  10. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    HaHA, it's no more important ady... my circuit is successful already by using a small 9v battery... Thanks all!!!

    But,

    There is a weird phenomenon that when the output voltage is too high(about 55 - 60v) the circuit will have a "hiss" sound~~ Does anyone here know where is the sound coming from? Is it from my inductor (5mH coil inductor)???
    But, why?
     
  11. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    http://services.eng.uts.edu.au/~venkat/pe_html/ch07s3/ch07s3p1.htm


    from equation 25 in this page...
    my spec is f=20kHz
    R=10kOhm
    D=0.75

    L = 1.3mH
     
  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I can't read the values in the schematic you posted.
    It might be that R3 or R5 are getting hot, C5 is over it's rated voltage, or other similar problem.
     
    xw0927 likes this.
  13. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    Things can go from "hiss" to "BANG" in a hurry... especially if it is a venting cap.

    It may be the coil windings vibrating, but better save than sorry.

    I am going to reccomend at least saftey glasses while hunting for this hiss.

    If it is an capacitor venting, and you are leaning over the circuit, looking at it, when the cap decides to "let go", you can be blinded by the steam, the electrolyte, or the flying metal and paper.

    BE CAREFUL

    If you notice any "pregnant" or "bulging" caps, or smell anything out of the ordinary, power down and wait for the sound/smell to stop before inspecting.
     
  14. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0

    C2 = 220uF,16v.
    C5=1uF,100v.

    R3=47k,variable resistor = 1k,R4=470(1/4Watt)

    It shouldn't be a problem of rating of my capacitor,as my output maximum =60V++(with sound of "hiss")At this moment, the inductor is 5mH.

    THing is strange, last night when I changed my inductor from 5mH to 3mH. The sound gone.

    However,today i tried again. My output is lower than it's supposed to be. And the sound "hiss" comes out again, in addition, my 3mH inductor is very hot this time.

    So, from my observation. The possible problems are:

    1. My battery ampere is low at this moment, it's a 9v non-rechargeable battery.

    2. The sound of "hiss" caused by my inductor.

    But, I couldn't find any information online regarding the noise created by inductor. So, I am asking help here... Thanks in advanced
     
  15. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    Thanks. But, if that is the problem of inductor, what should I do? Why is that inductor is problematic? Is it because my frequency is too high. At this moment, I temporary changed the frequency into around 7kHz only.
     
  16. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Are you certain that your inductor is 3mH, and not 3uH?
    A 3mH inductor would be rather large, even if wound with very small wire.

    The hissing might be coming from your battery. 9v "transistor" batteries aren't designed for heavy loads.
     
  17. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    yup, it is a 3mH inductor.
    I am using this type of inductor ( if no mistake, it is called coil inductor)
    http://www.littlebirdelectronics.com/product_images/k/935/180uh_coil0__04386_zoom.jpg

    OIC, my battery problem. Then I would try to change it. Thanks for your opinion.
     
  18. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If your inductor is getting hot, it's either going into saturation, or is not rated for the current that you're putting through it.
     
  19. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    The sound of "hiss" comes out again when i change my resistor into higher watt... previously i used 0.25Watt resistor, everything was okay. But, when I change it into 0.5watt 10k resistor, the sound comes out and resistor is getting hot over the time ( i didn't connect the supply to the circuit for very long when the 'hiss' sound comes out).

    in addition when the resistor is 0.5watt type, it will have a small spark when i connect the battery...

    So, my problem now is :
    1. Where is the 'hiss' sound coming from? From which component???
    2. The spark indicates??

    Sorry for my newbie questions...
     
  20. xw0927

    Thread Starter Member

    Dec 19, 2010
    114
    0
    anyone can help???
     
Loading...