Devices are not ideal, so some of the EXTRA components deal with the non-idealness.

Some quick things are parasitic capacitance and leakage currents. Bypass capacitors, usually 0.1 uF Ceramic capacitors at the power pins actually help compensate for the parasitic inductance of a PC trace. Without them, the part may oscillate. Pure CMOS chips cannot have their inputs floating.

hat leakage current needs a place to go. The leakage current combined with parasitic capacitance can cause an unconnected gate on a FET to suddenly turn on. Some parasitics are easy to identify, some not.

Take a piece of wire that sees a fan, so the wire can wiggle. That wire generates a really small current. A few pico-amps (1e-12) easily.
When your (me) setting up systems that need to measure near that level, it's something i have to take into account. Fundamentally, the wire is moving in the Earth's magnetic field, so it theoretically can generate a current and it does.

When dealing with high voltage, sharp points can be a problem.

Can wires have 90 degree bends in them. Sometimes yes. Sometimes no.

Yeah a lot of little things we have to know and each technology has its own set of insider secrets.

 

Why do not use circuit, recommended in datasheet?

View attachment 184646

Great Spot. Don't know how I missed this.

Thanks @Danko

 

i just thought that looking at such a straight line is informative.

Only if it tells the correct story.
In this case the transistor is not completely linear, so the linear trace is giving inaccurate info to a casual observer.
Look at the difference below between the linear plot and a log-log plot for the transistor and a resistor with a resistance equal to the high current value for the transistor.
The linear plot makes them look nearly identical whereas the log-log plot shows the significant difference.
Note that a log-log plot gives a straight trace for an Ohmic load, just as a linear plot does.

So i guess i am not sure if the extra info is good to have it seems like anyone using this would do much higher than 1ma say.
Maybe log for low stuff and linear for high stuff..

Extra info is always good when doing a design.
Most would likely be using it above 1mA but some may not.
If you don't need the info then you can just ignore it, but if it's important to your application (even if you may not realize it) and you don't know it's there, you might be hosed.

 

Only if it tells the correct story.
In this case the transistor is not completely linear, so the linear trace is giving inaccurate info to a casual observer.
Look at the difference below between the linear plot and a log-log plot for the transistor and a resistor with a resistance equal to the high current value for the transistor.
The linear plot makes them look nearly identical whereas the log-log plot shows the significant difference.
Note that a log-log plot gives a straight trace for an Ohmic load, just as a linear plot does.

View attachment 184659 View attachment 184660
Extra info is always good when doing a design.
Most would likely be using it above 1mA but some may not.
If you don't need the info then you can just ignore it, but if it's important to your application (even if you may not realize it) and you don't know it's there, you might be hosed.

Hello again,

Well i can see that if we change the aspect ratio to a more normal view we can see the nonlinearity of the linear plot (or log log plot) by looking at the very start of the plot, but i guess i can agree that both plots have their advantages and disadvantages.
If we deal with Ic less than 100ma it would be good to have that info too even though the normal applications this device is intended for will not need that.

 

Only if it tells the correct story.
In this case the transistor is not completely linear, so the linear trace is giving inaccurate info to a casual observer.
Look at the difference below between the linear plot and a log-log plot for the transistor and a resistor with a resistance equal to the high current value for the transistor.
The linear plot makes them look nearly identical whereas the log-log plot shows the significant difference.
Note that a log-log plot gives a straight trace for an Ohmic load, just as a linear plot does.

View attachment 184659 View attachment 184660
Extra info is always good when doing a design.
Most would likely be using it above 1mA but some may not.
If you don't need the info then you can just ignore it, but if it's important to your application (even if you may not realize it) and you don't know it's there, you might be hosed.

Here is something else to consider.
This is a similar plot of the 2N4403 i think is spec'd at 600ma maybe a bit more but check out the plot.
I would be interested to see what you get for this because i am seeing a fairly linear plot again.
One is collector voltage the other is collector current.

 

I would be interested to see what you get for this because i am seeing a fairly linear plot again.

Just click on the scales and change the plot to log for each axis to get a log-log plot.
Note the minus sign in front of V(c) since the log-log scales requires positive values only.
You may have to re-simulate to get the proper axis scaling



The 2N4403 looks similar to the FZT751 plot expect it has more intrinsic collector-emitter resistance.

 

Hi,

Yeah i dont use LTSpice that much but it's good to refresh.

Here are two plots using said sim.
Keep in mind that one transistor is rated 0.6 amps max and the other is rated 3 amps with 6 amps peak, then look at the plots and see what you think.

I am tempted to ask you to find one commercial application that uses the FZT751 at 50 to 100ma but that could be hard to find even if it exists.
On the other hand, i bet there are various applications that use the 2N4403 at 50 to 100ma.

 

am tempted to ask you to find one commercial application that uses the FZT751 at 50 to 100ma but that could be hard to find even if it exists.

And what would the lack of such an application for that transistor show/prove?
It would not change my statement that it's good to show the information at low currents, even if the application doesn't use the transistor at that current.
I think you are beating a dead horse at this point.
if you want to put blinders on and go with a linear plot for that data, that's your prerogative.
I will stay with the log-log plot.

 

And what the lack of such an application for that transistor show/prove?
It would not change my statement that it's good to show the information at low currents, even if the application doesn't use the transistor at that current.
I think you are beating a dead horse at this point.
if you want to put blinders on and go with a linear plot for that data, that's your prerogative.
I will stay with the log-log plot.

Hello again and thanks for your reply,

You can prove your point with pure logic you dont have to go into statements that seem to imply that you are right simply because it sounds like you are right. "put blinders on" is a statement that assumes the person saying it has some air of superiority, and it doesnt matter if they are right or not because what proves right or not right is logic, and only logic, and that is what people can agree or disagree with.

But let me see if i can bring that poor horse back to life by approaching this from another angle.

In the attachment there are two curves.
Which one is exponential and which one is linear?
If you want to you can think of them as being drawn on a log log scale or whatever scale you like.
You dont have to answer if you dont want to but it's interesting because i think this will bring the point home.

 

In the attachment there are two curves.
Which one is exponential and which one is linear?

Without context as to what we are looking at, I don't see that it's a pertinent question.

because i think this will bring the point home.

What point?

You want logic?
What is the logic is using a graph that doesn't show detail that the other does.
So far the only logic I've seen from you is that if the transistor isn't used at a low current then you shouldn't use a graph that shows that low current characteristics.
Doing that is what I mean by "putting on blinders".
And that's what we've been discussing.
What seems logical to me is that you always want to know as much information about a device you are using.

Please avoid the personal comments, unless you would like some back.

 

Without context as to what we are looking at, I don't see that it's a pertinent question.
What point?

You want logic?
What is the logic is using a graph that doesn't show detail that the other does.
So far the only logic I've seen from you is that if the transistor isn't used at a low current then you shouldn't use a graph that shows that low current characteristics.
Doing that is what I mean by "putting on blinders".
And that's what we've been discussing.
What seems logical to me is that you always want to know as much information about a device you are using.

Please avoid the personal comments, unless you would like some back.

Hello again and thanks for the reply,

Ok then i'll just concede. You are right i think more detail is better than less overall.
And thanks for the discussion.