Stocking up on mosfets - Electronic Circuits Projects Diagrams Free

birdman0_o · 10th May 2009, 09:38 PM

Hey guys,

I'm thinking of stocking up on mosfets sometime soon and I was just wondering if there is such thing as "overqualified" mosfets, in other words: Would it be wise to buy ~100 amp mosfets to use on any project? I don't see why there would be a problem, maybe just that they cost a bit more, perhaps they would be better suited because of the lower RDS?

Let me know what you think

Mike

Hero999 · 10th May 2009, 10:26 PM

Gernally the higher the power the better but higher specs do cost more.

Another thing to be aware of is that larger MOSFETs often have a higher gate capacitance and the maximum gate voltage on some low threashold high current types is quite low - I've seen some as low as 10V.

dknguyen · 10th May 2009, 11:12 PM

Other than cost, larger MOSFETs might have a lower RDson, but they also turn on slower (for a given drive current) increasing switching losses. Depending on what you are doing, they might run a lot hotter than you expect if you do not use sufficient drive even with a lower RDson because the RDson losses become negligible, but become dominated by the switching loss.

Sceadwian · 11th May 2009, 03:33 AM

By my way of thinking it seems best to buy three types. Small signal monolithics, medium power, and high power, with 25% going to P type and the rest N type. You'll want the small signal fets to be logic level, and maybe 25% of the power fets to be logic level. Not very common but depletion mode power fets have a place as well. Granted that's a lot of different types of fets, but you should cover your bases. Depends highly on what you think you'll be using the FET's for. I just covered what I think would be a general spread.

unclejed613 · 11th May 2009, 03:51 AM

if you're thinking of doing any audio stuff, you might consider getting lateral Mosfets, but beware of fakes. it seems lateral MOSFETS are high on the counterfeiting hit list because demand is high. same goes for the other MOSFETS as well. use suppliers like Digi-Key (i've seen their ads on this forum) or B&D, MCM, or Mouser. i know B&D has genuine laterals because i have bought them for an amp repair. 2SK1058/2SJ162 are excellent devices for audio amps.

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10th May 2009, 09:38 PM	#1
birdman0_o	Stocking up on mosfets Hey guys, I'm thinking of stocking up on mosfets sometime soon and I was just wondering if there is such thing as "overqualified" mosfets, in other words: Would it be wise to buy ~100 amp mosfets to use on any project? I don't see why there would be a problem, maybe just that they cost a bit more, perhaps they would be better suited because of the lower RDS? Let me know what you think Mike

10th May 2009, 10:26 PM	#2
Hero999	Gernally the higher the power the better but higher specs do cost more. Another thing to be aware of is that larger MOSFETs often have a higher gate capacitance and the maximum gate voltage on some low threashold high current types is quite low - I've seen some as low as 10V. __________________ I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong. Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.

10th May 2009, 11:12 PM	#3
dknguyen	Other than cost, larger MOSFETs might have a lower RDson, but they also turn on slower (for a given drive current) increasing switching losses. Depending on what you are doing, they might run a lot hotter than you expect if you do not use sufficient drive even with a lower RDson because the RDson losses become negligible, but become dominated by the switching loss.

11th May 2009, 03:33 AM	#4
Sceadwian	By my way of thinking it seems best to buy three types. Small signal monolithics, medium power, and high power, with 25% going to P type and the rest N type. You'll want the small signal fets to be logic level, and maybe 25% of the power fets to be logic level. Not very common but depletion mode power fets have a place as well. Granted that's a lot of different types of fets, but you should cover your bases. Depends highly on what you think you'll be using the FET's for. I just covered what I think would be a general spread. __________________ "Because I be what I be. I would tell you what you want to know if I could, mum, but I be a cat, and no cat anywhere ever gave anyone a straight answer, har har." Last edited by Sceadwian; 11th May 2009 at 03:34 AM.

11th May 2009, 03:51 AM	#5
unclejed613	if you're thinking of doing any audio stuff, you might consider getting lateral Mosfets, but beware of fakes. it seems lateral MOSFETS are high on the counterfeiting hit list because demand is high. same goes for the other MOSFETS as well. use suppliers like Digi-Key (i've seen their ads on this forum) or B&D, MCM, or Mouser. i know B&D has genuine laterals because i have bought them for an amp repair. 2SK1058/2SJ162 are excellent devices for audio amps. __________________ .................................................. .................................................. . E=mc² (+/-1dB) "If a curl of smoke is seen, the technician will soon experience the cause of difficulty"........ CTX arcade game rgb monitor service manual 1985 DC-to-Daylight Blog (on this forum): http://www.electro-tech-online.com/blogs/unclejed613/