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Topic: MOSFET Specs Clarification (Read 744 times) previous topic - next topic

Tomas1337

Hi,

So i'm beginning to use a MOSFET for a high amperage pulse application. I've been reading a lot about mosfets and have been getting conflicting information (maybe because of my understanding).

Im using the MOSFET, TK62J60W. If anybody can advise me with my questions, it would be a great help.

1. Whats the difference between Vgss and Vgs(that I keep reading about)?
2. It says that the Vgss is +-30V, does that mean that to turn on the MOSFET fully I need 30V?
3. It also states that theres an enhancement mode, Vth = 2.7V to 3.7V; Vds=10V & Id=3.1ma. Does this mean that if I apply 2.7V it will only allow 10V,3.1mA through the Drain and source?

Thanks!

liuzengqiang

This transistor seems to be compatible with 5V or higher logic. With 2.7 to 3.7V you are barely turning it on. With 5V, it is on. The figure 8.1 on the spec sheet has the lowest VGS=5V, indicating it is intended for 5V or higher input logic. That diagram tells you how much current can pass the transistor vs. how much voltage the transistor drops. If you apply 2.7V, you may get nothing.
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Koepel

#2
Oct 22, 2015, 09:30 pm Last Edit: Oct 22, 2015, 09:32 pm by Koepel
The Vgss is the voltage at which the mosfet will break down.

The "enhancement mode" is just a name. They don't even explain it. I think you are right, at 2.7V only 3.1mA goes through drain and source (with drain voltage at 10V).

Look in the datasheet for the graph with Vgs at the x-axis and Id at the y-axis. You see that it starts working at 4V and at 5V is can do 20A, it needs 7V for the full max current (but only pulsed current are allowed at those high currents).

This is Sparkfun's choice for a mosfet that goes well with an Arduino : https://www.sparkfun.com/products/10213
That one starts working at 2V.
If that is not enough current, you may put a few parallel.

MarkT

Hi,

So i'm beginning to use a MOSFET for a high amperage pulse application. I've been reading a lot about mosfets and have been getting conflicting information (maybe because of my understanding).

Im using the MOSFET, TK62J60W. If anybody can advise me with my questions, it would be a great help.

1. Whats the difference between Vgss and Vgs(that I keep reading about)?
Same thing, the key thing is the phrase "absolute maximum" - ie you don't go there, or even close.
Quote
2. It says that the Vgss is +-30V, does that mean that to turn on the MOSFET fully I need 30V?
Absolutely not.  The gate drive is given with the Rds(on) parameters.
Quote
3. It also states that theres an enhancement mode, Vth = 2.7V to 3.7V; Vds=10V & Id=3.1ma. Does this mean that if I apply 2.7V it will only allow 10V,3.1mA through the Drain and source?

Yes.  Vth is the threshold voltage, the point it starts to conduct at all - nothing to do with gate drive level.  You
take the gate _below_ Vth to turn it off, but watch out for the large variation in Vth between devices.

The entry in the datasheet section 6.1 says it has a guaranteed Rds(on) of 40 milliohms with 10V gate drive.
That's the on specification, the most important thing on the datasheet.

If you don't know what an enhancement mode FET is, you've more reading - most MOSFETs are enhancement
mode.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

DrAzzy

All fets are either enhancement or depletion mode.

Enhancement mode = mosfet off when Vgs = 0, and you move it above (N-channel) or below (P-channel) source voltage to turn it on. This is what you'll almost always use.

Depletion mode = mosfet on when Vgs=0, and you move it below (N-channel) or above (P-channel) source voltage to turn it off. This makes depletion mode fets much less convenient to use.
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Koepel

I didn't even know there were "enhancement" and "depletion" types. I guess the "depletion" type is not used a lot.

Tomas1337

Thanks so much to the experts!

 I'm sure two or three of us learned something new from the advise you've given here. Indeed I've tried the mosfet out but only on a logic level voltage and it seems to be working fine.  I'll update you once I hook it up to my high amperage application!

pwillard

When just starting out... if you just want to buy a MOSFET for your Arduino project... google for "logic Level MOSFET".  It will likely save you some headaches.

MarkT

I didn't even know there were "enhancement" and "depletion" types. I guess the "depletion" type is not used a lot.
It is for JFETs.  There are 8 possible configurations, JFET or MOSFET, N-channel or P-channel, enhancement
or depletion.  Not all combinations are used / useful.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

aarg

Then there's the enhancement/depletion types that are used for electret microphones. They are doped so that VGS=0 is roughly in the linear portion of the response.
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

MarkT

Indeed, enhancement/depletion is a continuum, not a binary choice, its just where the threshold voltage
sits.  Power MOSFETs are almost always enhancement mode, as this is convenient for switching, and
power is all about switching.
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