Go Down

### Topic: Mosfet (Read 4057 times)previous topic - next topic

#### ted

#30
##### May 09, 2018, 05:44 pm
the word " triggering" means completely, especially when we talk about switching

#### Marciokoko

#31
##### May 09, 2018, 11:38 pm
Yes i understand that.  You asked me to specify my question and I said:

"what parameter(s) do I need to check on the mosfet datasheet in order to determine if my 5V mcu will be able to supply the required voltage to open the channel completely and consistently?"

So you replied (for the) completely (bit) = (look at the) gate triggering voltage.  Or at least thats what I understood from your reply.

So what Im saying now is that I dont see any "gate triggering voltage" parameter in the datasheets.

#### ted

#32
##### May 09, 2018, 11:52 pmLast Edit: May 09, 2018, 11:54 pm by ted
Just different name - threshold

#33

#### ted

#34
##### May 09, 2018, 11:55 pmLast Edit: May 09, 2018, 11:56 pm by ted
So if  turn on at 2V I see no reason why not at 5V

#### ted

#35
##### May 10, 2018, 12:10 am
I looked again on data sheet - threshold voltage min 1V - max 2V , so 5 V is to much, use voltage divider to make 5V middle of the min and max - 1.5V

#36

#### TomGeorge

#37
##### May 10, 2018, 12:17 am
I looked again on data sheet - threshold voltage min 1V - max 2V , so 5 V is to much, use voltage divider to make 5V middle of the min and max - 1.5V
NOOOOOO......
That is the range of the specification, Vgs threshold can be 1V to 2V.
This is when the gate BEGINS to operate and drain to source current flow, you need to put 5V to ensure Rds is at its minimum.
The Vgs max will probably be 20V so applying 5V to the gate will not cause any problems, just make the gate work.
Tom...
Everything runs on smoke, let the smoke out, it stops running....

#### Marciokoko

#38
##### May 10, 2018, 12:38 am
OK si are you guys saying that Vgs threshold is the parameter I should look at to answer my question?

#### TomGeorge

#39
##### May 10, 2018, 01:15 am
OK si are you guys saying that Vgs threshold is the parameter I should look at to answer my question?
Yes, Vgs threshold, as low as possible  1V to 2V ideal,     4V or higher is not Logic Level.
Tom...
Everything runs on smoke, let the smoke out, it stops running....

#### tinman13kup

#40
##### May 10, 2018, 01:22 am
Don't equate Vgs(th) with Rds(on). The values given in Rds(on) include the gate voltage required to fully form the channel. Vgs(th) is the voltage required to only start forming the channel, in which high current loads will cause heat due to the resistance.
Tom
It's not a hobby if you're not having fun doing it. Step back and breathe

#### ted

#41
##### May 10, 2018, 02:42 am
Post # 37 and 39 are confusing me.

#### allanhurst

#42
##### May 10, 2018, 02:55 amLast Edit: May 10, 2018, 03:00 am by allanhurst
I haven't looked all the the way through this thread, so please forgive me if I've missed some points.

If you look at an enhancement mode mosfet's datasheet it gives lots of curves of Ids vs  Vgs under various conditions.

That should tell you what you need to know.

To reproduce those measurements requires rather more sophisticated equipment than an arduino output as a gate driver.

Allan

#### Wawa

#43
##### May 10, 2018, 03:23 am
Post # 37 and 39 are confusing me.
Maybe you understand it better with a LED as example.

A LED won't work if you put 0.1volt, or 0.5volt, or even 1volt on it.
But at a certain voltage, it STARTS to glow.

That is the THRESHOLD voltage.
You could say, the point that it is just turning OFF (coming from a higher voltage).

You need to be below that threshold voltage for a fet to be OFF.
So it's important to know that TURN OFF point.

But, as with the LED, you need much more to fully turn it ON.
Leo..

#### ted

#44
##### May 10, 2018, 03:27 am
Lot of theory in this thread, I will start with testing - post # 35, use 10k potentiometer as voltage divider

Go Up