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Are mosfets

KC2OST

BANNED
Mar 4, 2007
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Are mosfets more durable then transistors used in radios?
Do they hold up longer to a high swr?
What about high input voltage? Like 16v.
 

Librium said:
Are mosfets more durable then transistors used in radios?
Do they hold up longer to a high swr?
What about high input voltage? Like 16v.

there durable yes and cheaper then transistors!
as for Running with High SWR's , nothing is really good for that:LOL:
example:you have a 100 watt stereo amp and 50 watt speakers
crank it for a while and see how long its lasts, Same difference!
IT's going to blow because of feedback and or heat!!!

I would have to say it depends on the rating for this Mosfets for voltage!(in my eyes all the ones i worked with run warm anyway!)
I have been running them at 15.5-7 ..don't know if its killing the life % of them as there still kicking strong!!!

now,this is not a rummor i do this almost every day
like a Ford ---Fix Or Repair Daily:LOL:..not a insult ,I own a ford:)
Course 3/4 of the stuff i get in is user error,hooked up wrong,overdrivin,wrong setup or replace parts with the wrong values(caps and resistors)!!!
Enjoy!

Just my opinion, 1 costs more then the other :roll:
 
ken white WROTE:
MOSFET's are less durable than a BJT. They are easily damaged when over voltaged

Now thats funny:LOL:
I wouldn't say that unless you work with them and I do alot!
They are superior to the BJTs in high frequency applications where switching power losses are important. Plus, they can withstand simultaneous application of high current and voltage without undergoing destructive failure due to second breakdown.
Power MOSFETs can also be paralleled easily because the forward voltage drop increases with increasing temperature, ensuring an even distribution of current among all components.

I see some that have a min of 30volts compared to a BJT's that starts breaking down at 25volts.
BJTs suffer from thermal runaway. Their forward voltage drop decreases with increasing temperature causing diversion of current to a single device when several devices are paralleled.
This is why a big heat Sink is needed!
Mosfets don't need them ...but i use them for safety!
and this my friend is why we have MOSFETS...
I even have some 150 watt ones..and rated at 100A so i don't even try to fire them up all the way!
 
Hey lords. I am going to give you some friendly advice. Tuck tail and run. That dude is way out of your league.

Mopar
 
mopar2ya said:
Hey lords. I am going to give you some friendly advice. Tuck tail and run. That dude is way out of your league.

Mopar
A) I don't run from no one!
B) I been doing this Hands on for 25 years! and the testing of stuff/Mods!
C) I don't debate with no one!(and not in a forum!)
D) This is my Facts of hands on life ,I don't care who says what
MY stuff i mod and or fix doesn't have a bad rate of comming
back 99.8% of my mods or repairs ain't made up from junk or here say!
E) I am here to help all i can with facts! from my past or some good sources from past Company's I did help out in the electronic Fields!!!!
F) If you don't know me don't judge me!!! as of league I think your in the wrong ball park for even making a comment about me!

Enjoy!
 
mopar2ya said:
Hey, your call! Good luck!

Mopar
erm, ok and whats that all about...
forums are all about help suggestions and hands on and of course opinions!

As for debating, well lets just say i see a lot of head banging in this forum and on the other hand i see posts from months old not answered and are easier then most questions
so if a opinion has to take a challenge...good luck with getting one out of me! i take no part of it and won't ever ..BTW i see some love doing it and then i also see the main question never gets answered..
but looking on the bright side of this Forum i can see who's ,who
just by missing a detail here and there!

Peace!
 
Good Lord lords what's with all the ! marks? Lay off the coffee man. :LOL: What is really funny is that you work with MOSFETS all the time yet you erroneously call them CMOS. Now THAT is funny. ;) What Ken said is true to a point,MOSFETS can be easily damaged by being over volted.Just because a device is speced to operate at 50 volts means nothing. The point is at what voltage will that device be damaged. I have run MOSFET's in RF service in commercial equipment and they were speced at 50 volts.They were MRF-151G's BTW.Typical Vcc was 46 volts and the manufacturer clearly stated not to exceed 55 volts or the devices may fail.That would be at only 10% above typical operating voltages. BJT's are a little more forgiving,after all look at the all the over volted radios and amps out there.Now this may be a case of comparing apples to oranges as I am sure there is the exception to the rule. The annoying thing I dislike about MOSFET's is that they are susceptible to being destroyed by static simply from handling.that alone makes them a bit less durable compared to BJT's in my book.
 
QRN, I agree... :D

Lords, do me a favor since you are such an expert...

Please download 2 equivalent data sheets, one for a BJT and one for a MOSFET device and then open them side by side. Now look closely at the "Absolute Maximum Ratings" Tables and tell me what you see? I’ll bet there are many more limits placed on the MOSFET than are placed on the BJT…

One of the main reasons I say MOSFETs are not as durable as a BJT is due to ESD, exactly as QRN has stated. Many times a MOSFET will not be completely destroyed but will be damaged by ESD and performance will suffer. A BJT doesn’t suffer from this problem.

Now for your cut and past comments,

http://www.irf.com/technical-info/appnotes/an-1084.pdf

you really should look at the graphs that go with the comments you cut and pasted. If you had, you would have seen the BJT has a much greater safe operating area than a MOSFET...

“…BJTs suffer from thermal runaway. Their forward voltage drop decreases with increasing temperature causing diversion of current to a single device when several devices are paralleled... They are superior to the BJTs in high frequency applications where switching power losses are important.... Plus, they can withstand simultaneous application of high current and voltage without undergoing destructive failure due to second breakdown... Power MOSFETs can also be paralleled easily because the forward voltage drop increases with increasing temperature, ensuring an even distribution of current among all components.”

While a MOSFET has some advantages over a BJT, a BJT also has some advantages over a MOSFET, but that wasn't the questions posed...

Oh and BTW, MOSFETs do suffer from secondary breakdown as well, just not the same way as a BJT…

Ken
 
I have a question for you lords. I have been doing a little light reading and came across the following in an article about MOSFET's. What is your opinion of this quote?

“Power MOSFETs have been replacing power BJTs in power application due to faster switching capability and ease of drive, despite the very advanced state of manufacturability and lower costs of BJTs.

Now, that kind of contradicts your assertion that BJT’s are cheaper than MOSFET’s, doesn’t it? Is this quote in error? Are you in error? Are MOSFET’s really more expensive than BJT’s? Is the author horribly misinformed?

Mopar
 
mosfets are easilly damaged by static charges as qrn said, he got it spot on,
when i was at colledge the tutor set up a mosfet switching circuit to demonstrate the effect,
he had the class walk past the circuit and as each person passed the circuit we had to touch it with our bare hand then turn a switch on and see if the lamp illuminated,
guess what after maybe 10 people had touched it without any static disipitive strapping the device failed,
he did this because most folk wont believe how easilly mosfets can be zapped if propper attention is not paid to discharging your body and equipment when you work on these devices,
the device he demonstrated the effect with was no tiny fet it was a medium power fet, if you work on them without the propper attention to the details you have no idea just how much or little damage you have done to the device, it only takes one person with enough charge in their pants to destroy a perfectly good fet,
next time you climb out of your car and get a crack from the static or go to shake someboys hand and get a spark think about it, your hands can be a lethal weapon ;)
 
Good Lord lords what's with all the ! marks? Lay off the coffee man. Laughing What is really funny is that you work with MOSFETS all the time yet you erroneously call them CMOS. Now THAT is funny.
QRN.......!!!!!!!!!
sorry to see you don't like the !!!!!!!!!!!
i love coffee, maybe to much!
you work with pc's? or you just one of them dudes that debate with it??? or wait, i know a simple board changer:p
CMOS overclocking..Pc..Stereo amps, course this won't ring a bell to you..I wasn't only talking about CB's,or ham i was saying in general.
you need to lay off something and break that old door down and update!

ken white..
I see you did your homework and me copying and pasting
good job..well thats the only basic proof i can come up with.
when you work with something and jot down notes, do you really take the time to level it all out for a simple forum??
unless you have to...zenith use to tell me this to.
when i read there junked up wrong schematics for tv and updated them with a simple diode change in about 4500 units..



Lords, do me a favor since you are such an expert

i said that,wow i think your a word changer ,making something up out of the new guys word!
i said i do this stuff almost every day.
i didn't just say CB's now did I.

Please download 2 equivalent data sheets, one for a BJT and one for a MOSFET device and then open them side by side. Now look closely at the "Absolute Maximum Ratings" Tables and tell me what you see? I’ll bet there are many more limits placed on the MOSFET than are placed on the BJT

don't have to I already know this so when i do replace or mod a part did you also read that Mosfets make any board run more cooler and smoother on current..
Mosfets and ESD...well this is why some people need to keep there hands out of stuff...who said i overdrive Mosfets??
BJT break down and blow to..or just make a good radio sound like pure crap or feedback into the radio and blow it..
there is a lot of differences in MOsfets and BJT's i never said there wasn't.come to think of it i never blue a mosfet installing it
course doing it all the time helps not just reading about it..
course mosfets and BJT's hm who needs the bigger heatsink for the same output!!!! I wonder...

mopar2ya,
good man for reading up on this as one day they will be a standard item in everything....

“Power MOSFETs have been replacing power BJTs in power application due to faster switching capability and ease of drive, despite the very advanced state of manufacturability and lower costs of BJTs.”

yep there faster switching then anything out there over BJT's
and like i said IN general !!!
i pay 2-10 bucks for good ones in Stereo amps and .50-5 bucks for pc's ...lets not go there with pc's ....
as for linears just started in these i see mosfets that stomp the price of BJT's...no point there.and your basic BJT that is high in price over mosfets. so no one wins over this after all it was an opinion and a general statment!
we can go on all day and night about this..untill i see all of yous
hands on updating or making stuff with them..then come step up to the plate with me..hell i prob have more test equipment then all 3 of you's put together..
NOW GentleMan all 3 of yous missed the point it was my opinion and a general statement ,thats all ,don't have a grabber over this!
its not like anyones going to take your forum away...
and excuse my english and writing skills! never was good in it!
remember before the internet(which i do update that to)
there was a thing called HANDS on!!
remember this...
 

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