Linear lab power supply

[xavier60]

The Omron relay configures the two 15VAC secondaries as parallel or series to suit the output voltage.
The changeover occurs at about 15V.   The changeover threshold can be set to another voltage by holding the power button pressed for a few seconds. The new changeover threshold becomes set to the same as the present output voltage.
A blue LED indicates when the secondaries are in series which reduces the current capability.
The blue LED warns by flashing  if the Current Control is set to higher than what the transformer can safely output.

More: The updated schematic mainly has a CV anti-windup idea which was suggested by Kleinstein. The compensation feedback for the CV op-amp is now taken from the diode OR-ing node.

Minor schematic update 31/05/19

[JuanGg]

The Omron relay configures the two 15VAC secondaries as parallel or series to suit the output voltage setting.
The changeover occurs when the output is adjusted to over 15V. If needed, the changeover threshold can be set to another voltage by holding the power button pressed for a few seconds. The new changeover threshold becomes set to the same as the current output voltage.
A blue LED indicates when the secondaries are in series which reduces the current capability.
The blue LED warns by flashing  if the Current Control is set to higher than what the transformer can safely output.

More: The updated schematic mainly has a CV anti-windup idea which was suggested by Kleinstein. The compensation feedback for the CV op-amp is now taken from the diode ORing node.

Again, that is a really neat power supply!

All my power supply's files: schematics, PCBs, firmware, 3d printed parts, front panel overlay... are available here: https://github.com/Juan-Gg/Linear-lab-bench-power-supply/tree/master

And a short description over here: https://juangg-projects.blogspot.com/2019/05/linear-lab-power-supply.html
    Juan

[xavier60]

I can now confidently say that this topology can be made to work well.

[shoorup4eg]

I can now confidently say that this topology can be made to work well.

Hello
sorry for the necroposting.
I want to make a power supply with current and voltage regulation controlled by a microcontroller. I repeated the circuit in the simulator. This scheme does not work in the simulator. What am I doing wrong? The simulation file is attached (NI Multisim 14).

[xavier60]

Could you post just the schematic?

[shoorup4eg]

Yes of course

[xavier60]

I can't see anything wrong. Ill have a closer look when I get home. There is an updated schematic on another thread Ill link later.

[shoorup4eg]

I can't anything wrong. Ill have a closer look when I get home. There is an updated schematic on another thread Ill link later.

Ok. I'm waiting

[xavier60]

There is mainly a small change in the Emitter circuit of Q1.
https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg3582664/#msg3582664

[xavier60]

Yes of course

Just to be sure, the opamps  are upside down? I can't clearly see the pin numbers.

[shoorup4eg]

Just to be sure, the opamps  are upside down? I can't clearly see the pin numbers.

everything according to your scheme.
I can't achieve stable circuit operation in the simulator. I'm trying other designs now.

[uliano]

Q2 as a Common Base amplifier causes a possible complication.
Because it's non-inverting, the op-amp inputs had to be swapped.
When reference voltage  is connected to the inverting input and the feedback divider to the non-inverting input, the op-amp can't ever function as a true Miller Integrator. The minimum gain can never be less than unity.
For the voltage regulation loop, a small amount of proportional gain can and does improved stability.
For the current loop it is an uncertainty.
With Q2 as a Common Emitter amplifier again and a bit of tweaking, the response and stability are near as good as the Common Base version.

in this answer (#122) you introduce for the first time in the schematic the mysterious U1. My fault not having read all the messages in the thread, but I can't figure out what can it possibly be.

[xavier60]

Q2 as a Common Base amplifier causes a possible complication.
Because it's non-inverting, the op-amp inputs had to be swapped.
When reference voltage  is connected to the inverting input and the feedback divider to the non-inverting input, the op-amp can't ever function as a true Miller Integrator. The minimum gain can never be less than unity.
For the voltage regulation loop, a small amount of proportional gain can and does improved stability.
For the current loop it is an uncertainty.
With Q2 as a Common Emitter amplifier again and a bit of tweaking, the response and stability are near as good as the Common Base version.

in this answer (#122) you introduce for the first time in the schematic the mysterious U1. My fault not having read all the messages in the thread, but I can't figure out what can it possibly be.

The "U1" symbol is just the way DipTrace represents the power supply pins of the TLC072.

[uliano]

   I should have thought a little bit more over it and I could have gotten there