PNP not acting as in wikipedia

[yefj]

Hello , photos 1 to 5 represent a state where E>B>C which acctording to wikipedia its supposed to be a high current state called forward active.
but instead I get the opposite very weak current as if I am at saturation.
where did I go wrong?

 

[dick_freebird]

Are you able to pull 1.5mA through the left side of the diff pair, and stay linear on the front end?

 

[yefj]

Hello , I just want to see why my PNP is not acting according to the wikipedia definition.

 

[FvM]

"Very weak" versus "high" current can be both forward active. I don't get your point. Saturation versus forward active has nothing to do with a specific current level, just B-C voltage difference.

Would be a good idea to post the complete circuit, part of it is cut.

 

[yefj]

Hello FVM, Yes you are completly correct I am in active region but the emiter resistor is limiting the current.
How Is the resistor limiting exactly ? what is the mathematical logic of this resistor limiting the PNP?
LTspice file is attached.
Thanks.

 

[FvM]

R3 isn't limiting current in the first place. Current is set by a control amplifier formed of Q1 and Q2 that keeps voltage across R4 at constant 2V.

By the way, where's Ltspice syntax for time dependent resistors specified? I wasn't aware of it yet.

 

[yefj]

Hello FVM, Its a trick I for varying resistance, not something formal
So how do I stay in active region and increase the current?
Thanks.

 

[kd502]

Your circuit dosen't work as it should. You used two labels on one node vdd and o2. Ltspice can use only one, vdd was eliminated there is no connection between R2 and Vdd

 

[FvM]

Your circuit dosen't work as it should.

Measurements indicate that it's working though.

[Correction] I was referring to the results showing in post #1. Post #5 Ltspice schematic is corrupted and doesn't work. Kd502 is right, sorry for confusion.

 

[D.A.(Tony)Stewart]

Q2c was not = Vdd was one error from duplicate nets.

Varying the PNP collector R was not interesting since it's Vbe was fairly constant and Ib(Q3) quite low.

Although the time variable R can be useful in other places and even use negative resistance.

Yet without some specs, I don't see anything useful in this cct.