Aren't the characteristics different for the TO-18 can the (a) version the OP is using?

The thermal characteristics may be different but I don't think there's any significant difference in the electrical characteristics.

 

Hello,

Here I found a datasheet with a saturation curve:

On the corner there is stated they used Ic = 10 X Ib.

Bertus

Days after a question came to my mind;

This figure shows the saturated Vce and Vbe. So, as I understand from this figure is that this transistor is also saturated when the base current is 0.1 mA, where collector current is 1 mA. And if I tried to draw more than 1 mA, I wouldn't.

So, I would conclude that this transistor is saturated at any value of Ib in the range of 1-100 mA. Is this correct ?

 

Try read this
http://forum.allaboutcircuits.com/threads/bjt-saturation-question-s.81150/#post-577296
http://forum.allaboutcircuits.com/threads/which-method-npn.97963/#post-731172

 

..............................

So, I would conclude that this transistor is saturated at any value of Ib in the range of 1-100 mA. Is this correct ?

Depends upon the collector current.
It's reliably saturated when the base current is at least 1/10th of the collector current.

 

Depends upon the collector current.
It's reliably saturated when the base current is at least 1/10th of the collector current.

That's the point confusing me. Ic can be selected as 1 mA and then by choosing the Ib 1/10th of the collector current, which is 0.1mA, we would guarantee the saturation. And if I try to draw more than 1 mA current with any load attached to collector, I simply wouldn't.

That's what I think of. So, BJT would always be saturated if there is a current on the base, but the current we can draw would be dependent on Ib.

Am I correct ?

 

That's the point confusing me. Ic can be selected as 1 mA and then by choosing the Ib 1/10th of the collector current, which is 0.1mA, we would guarantee the saturation. And if I try to draw more than 1 mA current with any load attached to collector, I simply wouldn't.

That's what I think of. So, BJT would always be saturated if there is a current on the base, but the current we can draw would be dependent on Ib.

Am I correct ?

Not sure what you mean by "would always be saturated"?
To insure saturation you need to keep the base current at least 1/10th of the collector current. You can draw more collector current then that for a given base current but, at some point, depending upon the gain of the particular transistor you have, it will come out of saturation and the collector-emitter voltage will start to increase.
The point of saturation is not a hard point. The transistor gradually goes from being saturated to unsaturated as the collector current is increased for a given base current.

 

I don't think you understand what saturation means. It does not mean than you cannot have any more current. It means that Vce is miminzed for the given current.

If you put 1mA through the base, and draw 10mA through the collector, the Vce will be small, a fraction of a volt. If you have 10V across Vce, the current will be much higher than 10mA, and the transistor will not be saturated.

Bob

 

...Ic can be selected as 1 mA and then by choosing the Ib 1/10th of the collector current, which is 0.1mA, we would guarantee the saturation. ...

Let's turn this around. Suppose we select Ib to be a fixed 0.1mA, and then force a range of currents between 0.1mA up to about 20mA into the collector of a typical 2N2222. Here is a simulated plot of Vce as a function of the collector current, plotted log vs log. Note that for Ic = 1mA, the Vce is low. Even if we grabbed a '2222 with the lowest β, it would still work as a switch at Ib=0.1mA at an Ic=1mA.



Note what happens (for this typical '2222) with a base current of 0.1mA when the collector current gets close to 20mA. The β for this particular '2222 is ~200.

 

One more example: Here the collector current Ic is fixed at 10mA, and the base current is varied. Note the Vce=V(c) in the vicinity where Ib (x-axis) is about 0.1*Ic:

 

Not sure what you mean by "would always be saturated"?
To insure saturation you need to keep the base current at least 1/10th of the collector current. You can draw more collector current then that for a given base current but, at some point, depending upon the gain of the particular transistor you have, it will come out of saturation and the collector-emitter voltage will start to increase.
The point of saturation is not a hard point. The transistor gradually goes from being saturated to unsaturated as the collector current is increased for a given base current.

Okay now it's clear, I thought that Ic is limited by the selected Ib, but now it's obvious that I can draw more than selected Ic and that's the thing leads to unsaturated state.

Thank you.

 

Don't mix linear active region specs (Hfe = 100) with saturation specs Vce < 0.4 V @ HFE = 10). Although 22K will saturate the transistor in most cases, good design practice derates HFE or Beta by 30% for transistor variations. Also, temperature, end of life degradation, and resistor tolerances will cost you another 30%. Considering this, 10K is about the highest value you can safely use.

 

end of life degradation.

Glad to see this in writing.
In 1972 I was handed a Diagnostic Manual for the first Sears transistor TV. It took me one day to figure out that you could only go in circles with that manual because it never landed on, "bad transistor". Back then, the conventional wisdom was that transistors NEVER fail in ANY way. They don't degrade over time, there is never a bad one in a batch, and infant mortality doesn't exist. People thought the technicians were just, "tube jockeys", unable to learn the changes caused by transistor circuits, but look at what we had to work with!

So, thanks Ray. It always makes my day when a super high tech person validates my complaints.