MOSFET retrofit in switching power supply...

[GordonW]

OK. I'm venturing into realms I've not been into in an LONG time... MOSFET retrofitting.

Got a box of big, high-end car amps and such... most need repair. One of the first (Alphasonik PMA2100) uses MOSFETS in the power supply (switching step-up with transformer). Here's what I'm thinking of doing:


Replacing THIS (BUZ71A)
http://pdf1.alldatasheet.co.kr/datasheet-pdf/view/22132/STMICROELECTRONICS/BUZ71A.html

...with THIS (STP16NF06)
http://www.st.com/stonline/books/pdf/docs/7980.pdf

Anyone see any reason this shouldn't work?

AFAIK, the only real significant operational difference, is that the newer mosfet has lower capacitance... I'd think that SHOULD NOT really be a problem. HIGHER capacitance, sure, that can overload driving transistors... but LOWER capacitance? Looks like it might just slew a bit better (better efficiency?)?

The extra current and power dissipation capacity (20% greater current, 10% greater power dissipation) certainly can't hurt either!

So, any comments/warnings?

Thanks!

Regards,
Gordon.

 

[ifrythings]

I would go with some 70N06's for mosfets, they have 70A handling 60V rating and are .014 Ohm on resistence and are 150W dissipation

Gate cap, isn't a big deal in the slow speed switching (35KHz) and of course the drive transistors can take a bit more current than there use to.

 

[N-Channel]

I concur with ifrythings. Or better yet, try the IRF3205. Vdss = 55V; Rds(on) = 8mW; Id =110A, & Pdiss = 200W. Thjough the 70N06s should be plenty good enough.......

 

[GordonW]

With the toroidal power transformer, and the age of the design, I'd be worried about lowering the damping (raising the Q) of the transformer/MOSFET system (ie, inductive reactance interacting with the FETs), using a FET with THAT low of an on resistance (.008 ohms vs. .120 ohms). I don't want to have to possibly deal with current spikes as a result...

That's why I had looked at the STP16NF06... same range of on-resistance...

Regards,
Gordon.

 

[ifrythings]

I concur with ifrythings. Or better yet, try the IRF3205. Vdss = 55V; Rds(on) = 8mW; Id =110A, & Pdiss = 200W. Though the 70N06s should be plenty good enough.......

I will admit, the IRF3205 is an awesome MOSFET but it's expensive and is limited to 75A (maximum current of the TO-220 package as where the D² Pak (SMD-220, TO-263) can do the full 110A), It cost me 35 bucks (cad) just for 10 of them! As where the RFP70N06 only cost me <10 bucks for 10.

GordonW

I've done many upgrades of MOSFET's in car amps psu and never found any difference with current spikes as a result. I think this would matter if that design doesn't have snubber's incorporated.