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Topic: Inductor keeps getting smoked (Read 1 time) previous topic - next topic

seanz2003

I am trying to build a 5v 3amp switching regulator and things keep going awry. My latest failure involves an inductor that is obviously scorched (for the second time now). The voltage now oscillates between 5 and 6 volts. Before I go pop in another inductor, I was wondering if someone could clue me in to some of the pitfalls of this circuitry. What might be causing the inductor to burn up? Also, D1 is a pretty hefty diode which looks suitable for a three amp circuit. To contrary, the 100uH inductor (which I am assuming handles the load output) has some fairly thin leads- seems suspect to me. I am slightly ashamed to say but for a circuit that costs about $0.75, I have destroyed more than $2 in parts trying to get it right.  Any suggestions ? (besides using a 7805)
 

Grumpy_Mike

You need to know the rated value of the inductor, that will tell you how much current you can take. yes it takes all the current. It needs to be rated so your maximum current is not more than 70% of the rating.

Switch mode power supplies are very sensitive to circuit layout, without a good PCB it is almost impossible to get a reproducible circuit. Even with a good PCB layout I have seen many professional engineers take two or three goes at getting it stable under all current draws.

That is why you are better off buying a ready built module for this sort of thing.

CrossRoads

Are you following this?

C. Identify the inductor value from the inductor code, and select an
appropriate inductor from the table shown in Figure 3. Part numbers
are listed for three inductor manufacturers. The inductor chosen
must be rated for operation at the LM2576 switching frequency (52
kHz) and for a current rating of 1.15 × ILOAD. For additional inductor
information, see the inductor section in the Application Hints section
of this data sheet.

If you are smoking the inductors, I would hazard to guess you have not selected a hefty enough rated part.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
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seanz2003

Wow, I didn't even take a look at the rest of that data sheet. It makes a little more sense now.

mauried

This link will help you determine the relavant values.
http://www.daycounter.com/LabBook/BuckConverter/Buck-Converter-Equations.phtml

For Buck Converters, the Inductor must be able to handle the peak switching current without saturating.
The Peak Switching current is higher than the load current.

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