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I own a car audio amplifier which uses a DC to DC converter having a MOSFET of the type of FP50N06. However, after prolonged use, the three of the positive rail switching MOSFET cooked and smoked.

I was trying to replace that MOSFET, however, the FP50N06 is not available in my location so I had decided to replace it by readily available IRFZ44N MOSFET.

Here is the question: Can I replace it without major consequences? Thank you for your answer.

Based on your suggestions, here are the datasheets for the two MOSFET's:

Don't care about their difference in power. :)

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    \$\begingroup\$ It would be polite to link to the datasheets for both parts. That would encourage people to look at them to help you. It would be better practice to show why you think this replacement might work, and ask about any aspects you are unclear on. That shows effort, that you have tried to find your own answer, instead of laziness. \$\endgroup\$ – user_1818839 Mar 1 '16 at 16:06
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You should see pretty much the same performance from the IRZ44Ns. That is to say, they may well cook too.

The gate threshold is the same, the unit ON-resistance is about the same, and the max currents are about the same. So the IRZ44Ns should work just about as well as the original MOSFETs. And you do remember how well they worked, right?

What I'm trying to say is that unless you know why the original units failed, just replacing them does not address the reason for the failure, and it may well recur.

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  • \$\begingroup\$ Sir I was an IT student but I want to repair my Amplifier on my own, I knew a lot of things about basic electronics, however, I failed many times in troubleshooting an amplifier. Only the positive rail of the SMPS are cooked, but the negative rails are still in good condition. All the capacitors of both rails are working, also the fuse of the input power (+12V) did not tripped. So why is that sir? Thank you. \$\endgroup\$ – Mark Jhomel Olimon Mar 1 '16 at 16:21
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    \$\begingroup\$ The on resistance is not the same. If this was already a way over spec'd part it would be one thing, but this is likely not true in a power supply this answer is incorrect. \$\endgroup\$ – Brendan Simpson Mar 1 '16 at 16:23
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    \$\begingroup\$ @MarkJhomelOlimon - Sorry, I'm not psychic. Obviously the upper units cooked because they got hot. This suggests that the gate drive circuitry (and n-type MOSFETs used on the upper rails need special bootstrapped drivers) is getting flakey. \$\endgroup\$ – WhatRoughBeast Mar 1 '16 at 16:25
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    \$\begingroup\$ @bss36504 - 17.5 mohm @ 25 A vs 22 mohm @ 50 A is too close to say, particularly since the OP has no idea what current the FETs were actually running at. Or do you know for certain what those values are? \$\endgroup\$ – WhatRoughBeast Mar 1 '16 at 16:33
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    \$\begingroup\$ Ooh i done f*'d up. Carry on, while I go over here and hide. I had the wrong datasheet. \$\endgroup\$ – Brendan Simpson Mar 1 '16 at 16:44
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The IRFZ44N has

  • A higher \$Rds_{on}\$
  • A lower \$I_{d\_max}\$
  • A Lower \$V_{ds\_max}\$

than the FP50N06.

Don't care about their difference in power.

Well that's silly. Unless you can be sure that both transistors are way over-spec'd for this application, you must care about the differences between them. The \$Rds_{on}\$ in the IRFZ44N is 95% higher than the FP50N06 (at \$V_{gs}=10V\$).

Are you certain that at the current levels this FET will be operating under that you can afford almost 2x the power dissipation? The only thing that is for certain is that the IRFZ44N will produce significantly more heat than the FP50N06.

I suggest finding a better FET, there are literally thousands of them in that package that would do the job at least as well as the OEM solution, if not better. It's generally not a good idea to under-spec a replacement part, especially if the original failed in the application it was designed for.

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  • \$\begingroup\$ Thank you sir. I guess that something's wrecked the rail. Maybe slugs or trimmings of metal casing short circuited the positive rail, causing the MOSFETs to cook. I will try to replace the 3 positive as well as the three negative rail N Channel MOSFETs by IRFZ44N then I look forward to see the result. Thanks again. \$\endgroup\$ – Mark Jhomel Olimon Mar 1 '16 at 16:29

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