What in general terms is logic level for things like transistors.

I looked it up and it appears there are different levels for different applications ?

Could you expect a typical 'logic level' to be
in the range of 2 to 5 volts ?

 

"Logic level for things like transistors" is a meaningless statement.
Transistors do not have logic levels.
A transistor is a circuit element.
The input threshold of a circuit depends on the circuit topology.
The output levels of a circuit depends on the circuit topology and the power supply voltages.

You can design a transistor circuit to output logic levels at -100V to +100V or any voltage you choose.
I had to design a transistor circuit with logic levels to 1kV.

 

"Logic level for things like transistors" is a meaningless statement.
...

Logic Level Mosfet.

 

That is a different question altogether.

Check the spec sheets of the specific logic level MOSFET.

The popular IRLZ44 MOSFET spec sheet states the Gate Threshold Voltage VGS(th)
as 1.0V min and 2.0V max.

Halfway in between would make it 1.5V typical.
That is the input threshold voltage between the gate and source pins.

So to answer your original question, 2V to 5V would work (assuming the source is at 0V potential).

 

That is a different question altogether.

Check the spec sheets of the specific logic level MOSFET.

The popular IRLZ44 MOSFET spec sheet states the Gate Threshold Voltage VGS(th)
as 1.0V min and 2.0V max.

Halfway in between would make it 1.5V typical.
That is the input threshold voltage between the gate and source pins.

So to answer your original question, 2V to 5V would work (assuming the source is at 0V potential).

Thanks,

Does 'threshold' in this case mean anywhere in between the 1 and 2 v and of course the 1.5 volt is dead center (and probably a good point to shoot for) ?

 

and of course the 1.5 volt is dead center (and probably a good point to shoot for) ?

Absolutely NOT. 1.5V is undefined behavior.

In MrChips example, 1.0V and lower is interpreted as "low", 2.0V and higher is interpreted as "high". Anything in between these thresholds can result in undefined interpretations of the signal level, and in worst case scenarios cause some old ICs to oscillate and destroy themselves.

Are you talking about the transistor as a component, or are you talking about TTL logic levels (integrated circuits based on Transistor-Transistor-Logic)?

 

Correct, except for one thing: Current will flow from drain to source, not the other way around (unless you're talking about a p-channel MOSFET?)

 

Does 'threshold' in this case mean anywhere in between the 1 and 2 v

Yes, any particular MOSFET you buy can have a threshold anywhere between 1 and 2 volts and still be in spec.

the 1.5 volt is dead center (and probably a good point to shoot for) ?

Sure, as long as you are OK with half your products not working.

MORE then 2V is the place to aim here.

 

To confirm what Ernie is saying.
Read the specs carefully. VGS(th) is 1.0V min and 2.0V max.
Let us add to that a 0.5V margin of error.

What this means is that a logic low must be below 0.5V
and a logic high must be above 2.5V.

Hence you do not want to be anywhere between 0.5V and 2.5v for a valid logic signal.

 

Absolutely NOT. 1.5V is undefined behavior.

In MrChips example, 1.0V and lower is interpreted as "low", 2.0V and higher is interpreted as "high". Anything in between these thresholds can result in undefined interpretations of the signal level, and in worst case scenarios cause some old ICs to oscillate and destroy themselves.

Are you talking about the transistor as a component, or are you talking about TTL logic levels (integrated circuits based on Transistor-Transistor-Logic)?[/QUOTE]

Turning switch on turning switch off.

I understood (or mis understood) him to be saying the mosfet would close given anywhere between 1 to 2 volts to gate.

:shrugs:

 

To confirm what Ernie is saying.
Read the specs carefully. VGS(th) is 1.0V min and 2.0V max.
Let us add to that a 0.5V margin of error.

What this means is that a logic low must be below 0.5V
and a logic high must be above 2.5V.

Hence you do not want to be anywhere between 0.5V and 2.5v for a valid logic signal.

I hope I didn't say between .5 and 2.5 I thought you meant between 1 and 2 volts to gate would close the drain/source, and turn on a device that might be hooked up.

 

Correct, except for one thing: Current will flow from drain to source, not the other way around (unless you're talking about a p-channel MOSFET?)

I said it wrong, and N channel is what I'm going to be using.

Side question: do they use the term source as a nod to electron flow theory as oppossed to conventional, the actual flow being neg to pos, or source as reference to o potential ?

 

What the min and max specs are saying:

1) that none of the MOSFETs of this type made by this manufacturer will turn ON if the VGS is below 1.0V

and

2) all the MOSFETs of this type made by this manufacturer will turn ON if the VGS is above 2.0V.

 

Side question: do they use the term source as a nod to electron flow theory as oppossed to conventional, the actual flow being neg to pos, or source as reference to o potential ?

You'd be correct.

From Wikipedia: http://en.wikipedia.org/wiki/Field-effect_transistor

The FET's three terminals are:

• Source (S), through which the carriers enter the channel. Conventionally, current entering the channel at S is designated by IS.
• Drain (D), through which the carriers leave the channel. Conventionally, current entering the channel at D is designated by ID. Drain-to-source voltage is VDS.
• Gate (G), the terminal that modulates the channel conductivity. By applying voltage to G, one can control ID.

The names of the terminals refer to their functions. The gate terminal may be thought of as controlling the opening and closing of a physical gate. This gate permits electrons to flow through or blocks their passage by creating or eliminating a channel between the source and drain. Electrons flow from the source terminal towards the drain terminal if influenced by an applied voltage.

 

I said it wrong, and N channel is what I'm going to be using.

Side question: do they use the term source as a nod to electron flow theory as oppossed to conventional, the actual flow being neg to pos, or source as reference to o potential ?

Source is the source of electrons.

 

Source is the source of electrons.

How long before the rest of the world catches on , will it ever happen ?


Billions, trillions of components would need to be redisigned.

 

Source is the source of electrons.

Not in a p-channel MOSFET it isn't.

 

Side question: do they use the term source as a nod to electron flow theory as oppossed to conventional, the actual flow being neg to pos, or source as reference to o potential ?

I just read that the terms drain and source are a throwback to the water analogy for current flow. The water comes from the source and goes out the drain. I don't know whether what I read is true or not, but it has a certain simple logic to it.

Remember that MOSFET gates are switched by voltage levels, not current levels. In my limited experience, MOSFETs will often switch reliably below their rated gate voltage. So if you are building a one-off circuit, you can often get it to work with gate voltages that are less than the minimum spec'd by the manufacture. However, the manufacturers don't guarantee that, thus doing so is certainly not good for products that are going to be commercially produced, but hobbyiests often do so.

 

I just read that the terms drain and source are a throwback to the water analogy for current flow. The water comes from the source and goes out the drain. I don't know whether what I read is true or not, but it has a certain simple logic to it.

Not in a p-channel MOSFET it isn't.

 

Correct, except for one thing: Current will flow from drain to source, not the other way around (unless you're talking about a p-channel MOSFET?)

I don't know if it's relevant to this discussion, but I think it's worth noting that a conducting MOSFET will conduct in either direction. A non-conducting MOSFET will conduct from source to drain via the body diode.