HI Everyone, I'm current a lab assistant and have a few questions as to an interpretation of GAIN.
I have 2 transistors that have similar specifications and I'd like to compare the Hfe s .
The first is a 2N3553 FROM TI and the 2nd 2N3553 RCA that we had in my college lab.
horizontal voltage is 10 voltage per division
vertically the current is 10 mA per division
number of step is set to 7
I did not turn the collector supply . The collect supply stayed in the same position for both transistors.

The Gains (Hfe) are different . The RCA hfe is 36 at step 1 and TI hfe is 22 at step 1. Both meet the specifications called out in the datasheet.
I am not too concerned that the transistors are good. I want to know about the Hfe curves .
Both have a frequency response test condition and should be tested at 50 Mhz. The 575 is DC only so I don't have the ability to test at the frequency.
My question is , Why does the TI part appear more response to increases in base current ? Why does the TI transistor have more 'steps' ? Is there any inference or insight some can offer as to why the TI part has more characteristic curves than the RCA part for the exact same settings and test
conditions ? Is the TI transistor more linear or " controllable " as the GAIN increases ? Does that make is easier to bias the TI transistor ?
Any advice or insight to the curves would be greatly appreciated.

 

Ahh, the old 575.
I have spend many hours characterizing transistors on one of those way back when.

Why does the TI part appear more response to increases in base current ?

I would call that less responsive.
It's due to its lower Hfe current gain.

Why does the TI transistor have more 'steps' ?

Again because of its lower Hfe.
The higher gain unit is saturating (fully on) at the higher base current values by the value of the collector (Dissipation Limiting Resistor) you have chosen, which appears to be 500Ω as determined by the bottom right knob below.
If you reduce its value or reduce the value of the base current steps, then it will have the same number of steps (but spaced further apart) as the lower gain unit.
Just be careful that you don't overheat the transistor (may requiring lowering the peak voltage value).

Is the TI transistor more linear or " controllable " as the GAIN increases ? Does that make is easier to bias the TI transistor ?

Not sure what you mean by "controllable".
The main effect is that the higher gain transistor will require less base current to bias for a given collector current, and/or can allow a higher gain when configured as an amplifier.
There is no particular advantage to having a lower gain and it has little effect on linearity (however you define that).

 

Thank you for your answers. As a follow up, I hear the term 'linearity' frequently used in transistors that have a frequency response. I thought that if the TI transistor had 6 steps and all those GAIN curves, that building a load line would make it easier, so I thought that load lines had something to do with linearity. Does 'linearity' have anything to do with load lines or is it something else ? Did you every attach a spectrum analyzer on the output port of the 575 ? Did it work out ? Big Thank You in Advance.

 

As a follow up, I hear the term 'linearity' frequently used in transistors that have a frequency response.

And what does that mean to you?
All transistors have a frequency response.
There are several types of transistor "linearity" such as change the Hfe gain with large current (large signal) variations, and the change in transconductance for small signal variations, so you need to determine which linearity you are referring to.

I thought that if the TI transistor had 6 steps and all those GAIN curves, that building a load line would make it easier

You don't "build" a load line so there's not really degrees of "easy".
It's simply a function of the collector load resistance versus the collector current (red line below):
If you trace the slope of the right edge of the 575 display current-steps in your pictures, you will have the load line.
The number of steps makes no difference in that line.

Did you every attach a spectrum analyzer on the output port of the 575 ?

Never even thought about it, since a spectrum analyzer measurement only has meaning for AC signals, not the DC measurements that the 575 does.
What would you expect to see from the analyzer?

It would seem you need to look at some tutorials about transistor theory of operation, biasing, and amplifiers, as your knowledge appears rather minimal.

 

The TI transistor shows more steps because the hFE is lower.
The RCA transistor shows fewer steps because it has run out of headroom (50 mA).

The spacing between the lines gives an indication of linearity or non-linearity.
When the spacing is the same, the gain is constant across the displayed range.
When the spacing is not the same, then the AC gain will vary, hence non-linear.

 

Thank you for the information.

 

The Gains (Hfe) are different

That's because the device have a range of current gains.

This is for a Philips variant: