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Why is my mosfet getting so hot?

I'm following the basics of this instructable which is using an arduino to control an RGB led strip.  I am using a typical 300 count smd 5050 light strip powered with an old laptop 12v 5a adapter.  I'm using 3 irf530n mosfets but only the one attached to the red leds get hot after just a few minutes of being on full power.  I'm wondering if there's anything about that mosfet that would be causing it to only heat up on the red line.  I've tried replacing the mosfet and swapping them with the other colors and still it's only the mosfet that's connected to the red lights that gets hot.  I've tried measuring the current across the mosfet and it's about .6a for the green and blue, and about .8a for the red. I'm pretty new at this, so if there's anything else I can test I'll try to do.  Thanks for any help you can provide.

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-max-2 years ago

You need to pull the MOSFET into conduction, so apply at least 10V to the gate. Use a 2N2222 transistor wired in a common emitter setup (infinite gain) to allow the gate to rise up to the highest supply voltage available when a current is applied to the base. Note: This will invert the MOSFET, so if the output of a controller is PWM, the lowest setting will be high, and vice-versa.

bigbadassdave (author)  -max-2 years ago

Thanks for helping max!

So I can't understand why in its current state the circuit doesn't work. Is there something in the datasheet that would explain why this mosfet would get hot? Or in another words, how did you know that using a 2n2222 transistor would resolve this issue? Also, why do you suppose that only the red line is the one that is getting hot and not the other 2 colors?

rickharris2 years ago

Usually this is because the FET isn't being turned fully on - in this condition it still has some resistance to current flow resulting in converting this to heat.

You need a FET that uses 5 volts for the gate to use with a microprocessor.. Check the spec for your device.

bigbadassdave (author)  rickharris2 years ago

Hey thanks for getting back to me!

What am I looking for in the specs. According to the data sheet the Vgs is at most 20v and this falls under it.

Looks like your not driving the gate hard enough to turn the FET on fully.

This cct works and is from Picaxe.com make sure your not exceeding the current for the FET as well.

Capture 1.JPG
bigbadassdave (author)  rickharris2 years ago

Thank you for your help! I replaced the FET with the one in that diagram (irl520) And still the red one gets really hot. The other 2 don't seem to even get warm. I don't think I'm exceeding the current as when I tested the current it was less than 1amp. It's not making much sense to me, I was wondering if you knew some things that I could test out to see where this heat is coming from.