Hello,I want to test the PNP BIASING of my regulator I get only 2mA from the PNP Ic.
Is there a way to simulate a fluctuating load so I could see how well the regulator works?
Thanks.
LTspice file is attached.
https://www.onsemi.com/pdf/datasheet/2n3906-d.pdf

 

You can use a behavioral current source as a varying load.

 

... or you can use a variable resistor as a load.

 

Sim example below with the R4 resistance varying with time:
The green trace is R4's resistance.

 

Hello,I have implemented the varying resistor however I want to improve the PNP biasing situation in order to improve the voltage regulation on em_p node.
given the data sheet how canI improve the situation?
Thanks,

https://www.onsemi.com/pdf/datasheet/2n3906-d.pdf

 

I want to improve the PNP biasing situation in order to improve the voltage regulation on em_p node.

Over what current range?
What regulation stability do you want?

 

Currently the current in pnp is about 3 mA
Which far below what is can produce .
10-50mA regulation would be good .
How do you reccomend to get the regulation better ?
Thanks .

 

How do you reccomend to get the regulation better ?

What regulation accuracy and voltage out do you want?
Can you live with a different circuit?

 

Hello ,2V +0.01V will be great.
Yes I can live with other circuit .
Thanks.

 

10-50mA regulation would be good .

2V +0.01V will be great.

Below is the sim of a simple regulator that uses the TLV431 inexpensive, programmable 1.24V reference to control the output voltage:
The output changes <0.2mV for an output load current change from 10mA to 50mA.

 

Hello Crutshow, Could you say what BIASING state should the NPN be in so the regulator function properly?
Thanks.

 

Hello Crutshow, Could you say what BIASING state should the NPN be in so the regulator function properly?

R1 needs to have a value which will supply base current to Q1 for its minimum spec'd gain (beta) and maximum output load current, and at least 1mA to U1, both for the minimum input voltage and the maximum desired output voltage.
The R1 value I choose gives well above that minimum requirement, since it is supplying about 2.5mA for both Q1 and U1.

The feedback from the output causes U1 to sink any current that Q1 doesn't need/use to maintain the desired output voltage and current.
U1 starts conducting when the Ref voltage at the junction of voltage divider R4 and R5 reaches 1.24V (2.0V at the output).

Of course the simplest circuit for your requirements would be the common LM317 programmable regulator (below):

 

Hello ,purely out of analog curiosity of the previos circuit.
As you can see in the as my load increases my regulation get worse.
How can I improve the regulation in this circuit?
What is the analog intuition behind the faulre to regulate?
Thanks.

 

What is the analog intuition behind the faulre to regulate?

The poor regulation is because the design has low feedback loop gain.

What is the supposed purpose of R5, as it's not needed, and greatly reduces that loop gain?
Replace it with a short.
The only information of interest from the PNP data sheet its current-gain (β) at the output load current.

 

Here one way to vary the load: