What are the reasons cause the inductor in a boost converter burst

Discussion in 'General Electronics Chat' started by xw0927, Dec 19, 2010.

  1. xw0927

    Thread Starter Member

    Dec 19, 2010
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    What are the reasons cause the inductor in a boost converter burst.....HELP HELP>..
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Define "Burst"? Did the heatshrink around the windings break, or did the wires vaporize?
     
  3. xw0927

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    Dec 19, 2010
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    burst, the whole inductor is burned and the insulator of the jumper connected were slightly melted....so what the reason cause inductor burst like that??
     
  4. thatoneguy

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    Will need quite a bit more info.

    Schematic for starters. Input voltage/current, output voltage/current, and what was happening when it failed.

    A photo may also help (both sides of circuit board)
     
  5. xw0927

    Thread Starter Member

    Dec 19, 2010
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    it is just a simple basic boost converter which i used a 555timer as a pulse generator(about 20kHz)

    I used a inductor(470uH), I don't know the rating of its, it looks like the resistor with colour code.

    The input voltage is a battery of 12V,1.2A... Is it the problem of battery rating?

    I couldn't get the output voltage, as it was burst a few second after i connected the battery...
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Sounds like too much current from here. What is the gauge of wire used on this inductor and what is the current?

    If you are trying to use a small choke that is likely the issue, you would be pushing it for ½ amp. For an amp you need to buy one rated for it or roll your own.

    I've been working on similar projects, but the 555 version is a bit off in the future. I am one of the local 555 experts around here, and have been writing articles and tutorials during my stay.

    Bill's Index

    My Cookbook

    The 555 Projects

    LEDs, 555s, Flashers, and Light Chasers

    As that one guy has stated we really will need schematics at a minimum.
     
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  7. xw0927

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    Dec 19, 2010
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    So, you mean, most properly, it is my inductor rating problem?
    Too bad, there is no shop selling inductor around my home...
    Anyway, thank a lot...

    1 more thing, I want to ask is:
    Do I need to connect in parallel to the voltage source(battery) in my circuit? What is actually the function?
     
  8. xw0927

    Thread Starter Member

    Dec 19, 2010
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    Sorry, new here... how could i upload a photo here? thanks in advanced.
     
  9. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    You already did attach an image to a previous post.

    This is given in the FAQ:

    Bertus
     
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  10. SgtWookie

    Expert

    Jul 17, 2007
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    A 1N4002 is a standard rectifier diode, and does not turn off quickly enough for a boost converter. You need a fast recovery type diode, or a Schottky diode.

    You don't show a feedback path for voltage control. This may cause the output voltage to become very high, particularly with such a small load (20k Ohms).

    I suggest that you read through Ronald Dekkers' fine "Flyback Converters for Dummies" page:
    http://www.dos4ever.com/flyback/flyback.html

    He shows how to use fairly commonly available source material to build your own inductors, and how to measure them.

    In his Figure 3 and Figure 16 schematics, replace R4 with 47k maximum, as this will limit the output to ~<=50v; much more safe for a budding hobbyist. Please keep safety in mind at all times.
     
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  11. xw0927

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    Dec 19, 2010
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    Thanks. I noticed the problem of diode also. I did read the page before but I didn't know how extractly the control feedback system works. To make the voltage goes in to the npn greater than 0.7V is enough,right?
    Do you have any suggestion for the npn I should use, my target output is 45V.

    really thanks alot...
     
  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    The best solution for inductors is to order some ferrite cores and wind your own to the value you need. Typically one type of toroid mix that you have the data for on how many turns you will need.

    The resistor sized inductors cannot handle very much current at all, as you've found out.
     
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  13. SgtWookie

    Expert

    Jul 17, 2007
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    The 1N400x and 1N540x series diodes are pretty much the same, except for the current rating (1A vs 3A); they are for rectification of AC voltage that's under 500Hz. When you're in the medium kHz range, they turn on fast enough; it's just that they don't turn off fast enough.

    Pin 5 on a 555 timer is the control voltage pin. Inside a standard 555, there is a voltage divider made up of three ~5k Ohm resistors that set the trigger and threshold levels; normally at 1/3 and 2/3 Vcc.

    Referring to Ronald Dekkers' page, as the voltage on the output of the boost or flyback converter goes higher, the voltage on the base of the NPN transistor goes higher, eventually turning the NPN transistor on, which pulls the CTRL pin 5 low; this has the effect of both increasing the frequency of the 555 timer, and decreasing the ON time of the MOSFET.

    Are you talking about the transistor on pin 5, or the MOSFET that's shown on Ronald's page?

    A 2n2222 for the NPN on pin 5 and an IRF510 would work OK for the MOSFET.

    If you're talking about the NPN transistor in your circuit, then you would need a transistor rated for at least 50v.

    Instead of a transistor, I suggest using an N-channel power MOSFET.

    Are you in the USA? If so, your local Radio Shack probably has all the stuff you need to make a basic switching regulator.

    Please put your general location in your profile. Click on the "User CP" text on the menu bar, then the "Edit your details" on the left menu, then scroll down and in the box to the right of "Location:", type in where in the world you are. Country and state or province (where applicable) is plenty good enough.
     
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  14. xw0927

    Thread Starter Member

    Dec 19, 2010
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    Ok, I will edit my CP later. I am a student in Malaysia.
    It is quite inconvenient to get some components that I want here as I live in a small city.

    Yup, I will use N-channel Mosfet as the "switch" in the circuit and npn in the 555timer feedback circuit.

    Hence, I will use 1N4148;IRF 740/IRF520;Do you think it is okay? Mostly, I can get 2n222 in the shop. I've uploaded my new circuit at below, hopefully, you can have a look at it. Btw, 1 more thing that I ain't sure with its function that is R6[Referred to my circuit] I put it as it's shown in Ronald Dekker's page but I don't know why, could you please explain in detail to me if you know?

    Another problem is: I do see people put 2 capacitor at the front end of the circuit where the place I draw a red circle. Do you think it is necessary? If yes, what is the function? Sorry to say that I am a real newbie in practical circuit design, and when I study the theory of boost converter, it doesn't show this part.

    Thank you for answering my question.
     
  15. xw0927

    Thread Starter Member

    Dec 19, 2010
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    Oh thanks again. I ordered some inductors from a website already. But, it doesn't show the picture of the inductors. Anyway, from your opinion, you mean the inductor burst is because of itself rating cannot withstand the 1.2A current, am I right?

    1 more thing is, i couldn't find the rating of resistor-like inductor. Basically, I don't know how to search it. Could you please help?
     
  16. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Not more than 100mA unless it is a very large resistor physical size.

    Did yours look like the top one in This Search? Anything of a higher current ends up physically larger, you would want something around 28 gauge wire minimum for the windings.
     
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  17. xw0927

    Thread Starter Member

    Dec 19, 2010
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    I couldn't see anything from that page.
    Oh, the resistor sized inductor could only withstand not more than 100mA. Haha, what a huge mistake I did... Thanks for explaining.
     
  18. xw0927

    Thread Starter Member

    Dec 19, 2010
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    erm... wanna ask that if i use 9018npn to replace 2n222 ok or not? I couldn't find the datasheet.. Sigh...
     
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