Not really.
Since R1 is 100k, the current through Q1 is just 148μA when ON.
This only requires a base current of 14.8μA for complete saturation.
With 5V applied to R2, and R2=R4=100kΩ, the base current is about 38μA, over twice needed for good saturation.
So the value of R2 and R4 of 100kΩ is more than adequate.

Before I came to AAC, when I using the transistor as a switch that I would like to using the practical values through the testing, and no matter the gain = Ic/Ib, or to setup Ib as 1mA or and Ic = 10mA, etc.,

Although through the real tested, when the Ib < 1mA, the Vce still can goes into the saturation region, but when I saw the helpers used the gain=Ic/Ib=10, and now, it seems that I get used to using the gain = 10 to calculate the Ic and Ib, and in the datasheet only noted that Ib = 1mA, there is no any other info to shows when the Ib less 1mA, how to calculate the Ic, of course using gain = 10 is more easier, how low the Ib can still keep the Vce stay in the saturation region, do you have any official documents to talking about this?

That's why I said that the 100K can't make Vce get into the saturation region, but in the real tested showed it can, so they have a little conflict each other.


2N3904 datasheet.


This thread was split from below for more discussion.
Push On/2sec Push Off/triggered 5 min delayed Auto Off Switch
https://forum.allaboutcircuits.com/...iggered-5-min-delayed-auto-off-switch.133494/

 

It's true the saturation voltage is only specified for high values of current but, in both cases, the gain is set to ten.
And there's no reason that value of gain won't work at low currents to insure saturation.

Below is the LTspice simulation of the circuit.
The saturation voltage at the collector is only 21mV, so I think the circuit is okay as is.

 

Yes, it's really could works at very low Ib current as 10~20 uA in the real world, maybe I need to pick up my original method that I got from the experience of experiments.

And thank you for reminded me that the gain=Ic/Ib=10 still could applied to the Ib<1mA, but I still want to see the official documents.

 

Yes, it's really could works at very low Ib current as 10~20 uA in the real world, maybe I need to pick up my original method that I got from the experience of experiments. And thank you for reminded me that the gain=Ic/Ib=10 still could applied to the Ib<1mA, but I still want to see the official documents.

https://www.fairchildsemi.com/datasheets/2N/2N3904.pdf

Is probably as close as you can get to empirical data unless you post what your experimental method and what it revealed for what, a single transistor ?

 

https://www.fairchildsemi.com/datasheets/2N/2N3904.pdf

Is probably as close as you can get to empirical data unless you post what your experiments revealed for the transistor in question.

Which section do you want to me see?

 

And thank you for reminded me that the gain=Ic/Ib=10 still could applied to the Ic<1mA, but I still want to see the official documents.

Well, the current gain for that transistor does drop off some at lower currents, as shown below, but I think a gain of 10 is still more than sufficient to guarantee saturation at those currents.


But I doubt you will find any "official documents" showing that for this transistor.

 

Well, the current gain for that transistor does drop off some at lower currents, as shown below, but I think a gain of 10 is still more than sufficient to guarantee saturation at those currents.
View attachment 123433

But I doubt you will find any "official documents" showing that for this transistor.

I saw the table shown Ib less 1mA, but ignore it, because the Vce does not at the saturation region as 0.2V.

According to what I tested a 2SC945, when the Rc=100K, and Rb increasing to 600K, the Vce is only around 30mV, when I calculated the Ib is quite low as Ib = (5V-0.583V )/600K =7.36uA.

Anyway it clarity my doubt why the Ib<1mA can't use gain = 10, since the Ib could works so low less than 20uA and still could make Vce get into the saturation region, and why there is no any official documents talk about it?

 

why there is no any official documents talk about it?

We use devices all the time at operating parameters that are not specifically defined at the values we are using. You just make the best engineering extrapolation of how it will work based upon the published data and engineering knowledge of how the device works.
You back that up with simulation and breadboard testing.
I don't see how you can expect "official documents" for every possible operating condition.

 

If you knew how to read a data sheet, you woudn't have to ask for help, and what you seem to be having trouble with is relating beta to low values of collector current.

You've stated, earlier, that you have some empirical data which supports your nebulous claim and, yet, you post opinion instead of fact.

We are discussiing about the gain = Ic/ib = 10, specially the Ib<1mA and Vce=0.2V, please point out where I can find it in your links?

 

I don't see how you can expect "official documents" for every possible operating condition.

You are right, but how I feel quite strange is why it just shown at 1mA/0.2V, but when Ib <20uA the Vce still could working in the saturation region, 1mA and 20uA or 10uA that is big different.

 

We are discussing about the gain = Ic/ib = 10, specially the Ib<1mA and Vce=0.2V, please point out where I can find it in your links?

Nonsense.

As I understand it, what we're discussing is about forcing Hfe to 10 for tiny base and collector currents, and it seems you're just being argumentative, since if you were really interested in the meat of the matter you'd contact the manufacturer, get definitive data for the part in question, and post that data here for all of us all to peruse and enjoy.

<SNIP>
Administrators note: there is no need to offend a moderator

 

Which section do you want to me see?

Take a look at figure 2 and, bearing in mind that Hfe is locked in at 10, extrapolate the rise in Vce(sat) as Ic diminishes until it reaches your criterion.


Like this:

 

@ScottWang
May I remind you that the base-emitter relationship is valid all the way down to picoamps.
There is no reason why the collector current can not be manipulated in that range.

 

And if a moderator refuses to accept correction, and the only way to wake him up sharp is to offend him, then what?
Rat him out to other moderators who'll only support his position?

Q: Did you wake up grouchy?
A: No, I let him sleep in.

 

Here's the Figure 2 that EM Fields is referring too.
The red dot below is approximately where the subject circuit is operating.
(Actually that circuit should have a somewhat lower saturation voltage since its base current is about 1/4th of the collector current, not 1/10th as in the graph).
And you could likely extrapolate the curves to less than 0.1mA collector current with reasonable accuracy, if you desired.


Is that official enough for you?