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Author Topic: Breaking fets  (Read 792 times)
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Finland
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Hello!

I have problem with fets. I used fets about few days with halogen lamps controlled by arduino and everything worked fine until my fets breaked down. They became hot and melted my breadboard. Why that hapenned? I'm sure I wired everything properly. I used 50 Watts 12 volts halogen lamps and this fet: http://www.partco.biz/verkkokauppa/product_info.php?products_id=5067

Thanks
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Elias Ojala

Finland
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And I didn't use heat sinks.
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Elias Ojala

Finland
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And still one thing. I think it dosn't affect, but I used three 12 volts power supplies.
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Elias Ojala

texas
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And I didn't use heat sinks.

I'd say that was the biggest problem.  This is not a logic-level FET and you aren't much above the gate threshold voltage so it's not turning all the way on with 5V gate voltage.  It might need a gate driver to switch fast enough anyway. You should look for some IRLxxx type parts, maybe an IRL540?
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Finland
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So do you think this: http://www.partco.biz/verkkokauppa/product_info.php?products_id=5070 can be good for me? And if I use that have I use heat sinks?
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Elias Ojala

Finland
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Sorry! I misspell. I didn't use http://www.partco.biz/verkkokauppa/product_info.php?products_id=5067 but I used http://www.partco.biz/verkkokauppa/product_info.php?products_id=5068

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Elias Ojala

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What kind of breadboard where you using? 50W @ 12V = +4A. You need some thick wires/traces for 4A.
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Finland
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I used this: http://www.partco.biz/verkkokauppa/product_info.php?products_id=4378
Wires in it are not so thick. But can it brake fet?
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Elias Ojala

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The breadboard is definitely wrong. The breadboard doesn't have good connectection and certainly not for such current !
Do you use 12V DC ? Not AC I hope.
Do you want to dim the lights with PWM, or only switching them on and off ?
The power mosfet is only 17 or 22A. Halogen lamps can be very nasty for the very high peak current during power on. You might want use a mosfet that can handle more.
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Finland
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Yes I used DC. But why can't 17A 70W fet handle one halogen which is only 50W? And I want to dim the lights with pwm if it's possible.
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Elias Ojala

texas
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So do you think this: http://www.partco.biz/verkkokauppa/product_info.php?products_id=5070 can be good for me? And if I use that have I use heat sinks?

Yes, I think the IRL540 will work without a heat sink It will be dissipating at least 750mW though, so it might get warm (~75C) but it shouldn't melt anything.  Is there any ventilation?  Is it in a warm environment, like anything above room temperature?
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Finland
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My lamps and fets and arduino etc. are in the table so there are some ventilation.
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Elias Ojala

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Yes I used DC. But why can't 17A 70W fet handle one halogen which is only 50W? And I want to dim the lights with pwm if it's possible.

The answer to that is in the datasheet.  It can only flow 17A if you can keep the temperature at 25C.  You have to derate that as the temperature goes up.  Once it gets to about 160C, it is only rated for 5A.  If you used a good heatsink, you wouldn't have any problems, but the IRL540 will dissipate less than half the power the IRL530 does at the same drain current.


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Yes I used DC. But why can't 17A 70W fet handle one halogen which is only 50W? And I want to dim the lights with pwm if it's possible.

70W is the maximum amount of heat the MOSFET can dissipate (as long as its kept cool enough), not the maximum load it can control.
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So do you think this: http://www.partco.biz/verkkokauppa/product_info.php?products_id=5070 can be good for me? And if I use that have I use heat sinks?

This one http://www.partco.biz/verkkokauppa/product_info.php?cPath=2075_11_1020_1872&products_id=5057 would be better, and wouldn't need a heatsink unless you use fast PWM.
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