I am a recent graduate in electronics, and I am working on an adjustable symmetrical voltage source with a current limiter that remains stable for any capacitive load. Since I am a recent graduate, I would appreciate assistance in analyzing this circuit. I would like to understand why the circuit oscillates when the output capacitors (C1 and C2) are removed and how these capacitors placed there ensure the stability of the power supply. I would also appreciate an explanation from someone more experienced regarding current and voltage control, as well as an overview of the general operation of the power supply.


Attached is the power supply simulated in LTspice and its corresponding library so that you can simulate it if you wish.


The complete power supply circuit (without the linear power supply) is used for simulation. I am still unsure why I can't simulate with the complete power supply circuit (with the linear power supply).





The entire library is too large to be shared here. So, I have uploaded it to Google Drive, and I will leave the link here for you to download.

https://drive.google.com/drive/folders/13cNf8YzybxsezZxV_cqKbCpJ0NyOv_CS?usp=sharing

 

Welcome to AAC!

I would like to understand why the circuit oscillates when the output capacitors (C1 and C2) are removed and how these capacitors placed there ensure the stability of the power supply.

Please post a schematic so we can see how the capacitors are being used.

Attached is the power supply simulated in LTspice and its corresponding library so that you can simulate it if you wish.

Are you certain that the simulation is working correctly?

 

Where is the circuit diagram,??

 

Welcome to AAC!
Please post a schematic so we can see how the capacitors are being used.
Are you certain that the simulation is working correctly?

The schematic is available both in the provided Drive folder and attached to this post. The simulation runs with my library in LTspice. Remove your entire library and replace it with mine. Don't forget to make a backup of yours before doing this. The LTspice library is typically located in C:\users\yourUser\AppData\Local\LTspice, and it is a folder called 'lib'

https://drive.google.com/drive/folders/13cNf8YzybxsezZxV_cqKbCpJ0NyOv_CS?usp=sharing

 

Where is the circuit diagram,??

The circuit is quite large, so I have made the schematic available for download. Nevertheless, I will try to post the circuit here broken down into sections with a brief explanation of each part.

 

The schematic is available both in the provided Drive folder and attached to this post.

What we want is an actual schematic, not LTspice files or archives. I can't load the .asc file without your libraries to do it for you...

 

What we want is an actual schematic, not LTspice files or archives. I can't load the .asc file without your libraries to do it for you...

This is the schematic.

Can you zoom in? I'm not sure if it's too small.

 

Too small for me...

 

Can you zoom in? I'm not sure if it's too small.

This what I get when I zoom in:


Better if you print to PDF and post clips:

 

This is the schematic.

Can you zoom in? I'm not sure if it's too small.

It's too small.
You can enlarge it on your screen until everything is clear, and then do a screen grab, which can then be pasted to your post.

 

I would like to understand why the circuit oscillates when the output capacitors (C1 and C2) are removed and how these capacitors placed there ensure the stability of the power supply.

Basic negative feedback control theory. Your closed loop gain must be below zero dB before the phase shift reaches an additional 180 degrees.
Have you made a Bode plot?

 

We start with a linear power supply capable of delivering approximately +30V at +B and -30V at -B.






This part of the circuit indicates that the power supply is on.






Here, we generate the voltages of 5V and 10V, which are auxiliary supplies for powering the ICs and potentiometers.






Here, we generate the voltages of -10V, which are auxiliary supplie for powering the ICs.




Here we have a comparator circuit to indicate current overload on the negative output.



Here we have a comparator circuit to indicate current overload on the positive output.





Below, we have the circuit that regulates the voltage using a potentiometer.






Below, we have the negative part of the power supply.






Below is the positive part of the power supply.





Notice in the upper photo's corner the current limiter through a potentiometer. Below, enlarged.

 

Here, we generate the voltages of -10V, which are auxiliary supplie for powering the ICs.

The maximum current through the Zener is 20V / 220Ω = 90.9mA which will cause 909mW dissipation in the 250mW Zener, so it won't last long.
(You can see that in your simulation by doing an ALT-Left Click over the Zener after doing a transient or operating point simulation).

Why not use an LM7910 negative regulator for that?

 

The maximum current through the Zener is 20V / 220Ω = 90.9mA which will cause 909mW dissipation in the 250mW Zener, so it won't last long.
(You can see that in your simulation by doing an ALT-Left Click over the Zener after doing a transient or operating point simulation).

Why not use an LM7910 negative regulator for that?

Actually, this zener diode is 10V 1W.

I used what was available in the simulator at the time of simulation.

 

Basic negative feedback control theory. Your closed loop gain must be below zero dB before the phase shift reaches an additional 180 degrees.
Have you made a Bode plot?

Thank you for the tip. I studied the theory and created the Bode diagram.
Now I understand
I have one more question. How can I understand the current control by the transistors T4 and T5?