Oscillation in PSU simulation

[ElectronSurf]

1 mA in 0-1A with three OP07. actually LM324 was showing some good results too, ~±3 mA error considering the resistors error it was good for a cheap op amp but only with a 1 ohm shunt.

Appreciate it if you post an schematic of that RC filter and thanks for all the information.

[Zero999]

Here's a schematic I drew up. The problem is the transient response is poor. RL is a time dependant resistor. Its value is suddenly changed from 1k to 1R and the current and voltage are monitored. When the resistor value falls to 1R, the current shoots up, before the current limit kicks in and the voltage spikes, when the value rises to 1k again.

EDIT: I've just noticed the current limit on the schematic at the start of the thread is 1A, whilst on this circuit it's 2A. Obviously just change R2 to 1R for 1A.


 PSU Instr Amp.asc (4.05 kB - downloaded 50 times.)

[xavier60]

Would the voltage overshoot be acceptable with 100 milliohms for the CS resistor and 1A maximum load?

[Zero999]

Would the voltage overshoot be acceptable with 100 milliohms for the CS resistor and 1A maximum load?

Are you asking the original poster or me?

I don't see the need for such a low value current sense resistor in a linear power supply such as this. 1V or so of additional voltage drop, at full load should be acceptable. Going for very low values will increase the error, from offset voltages, especially at lower currents.

[xavier60]

Would the voltage overshoot be acceptable with 100 milliohms for the CS resistor and 1A maximum load?

Are you asking the original poster or me?

I don't see the need for such a low value current sense resistor in a linear power supply such as this. 1V or so of additional voltage drop, at full load should be acceptable. Going for very low values will increase the error, from offset voltages, especially at lower currents.

I was asking you since you already had it in a simulator. Maybe the voltage overshoot will be acceptable with an output capacitor added and faster compensation.

[Zero999]

Would the voltage overshoot be acceptable with 100 milliohms for the CS resistor and 1A maximum load?

Are you asking the original poster or me?

I don't see the need for such a low value current sense resistor in a linear power supply such as this. 1V or so of additional voltage drop, at full load should be acceptable. Going for very low values will increase the error, from offset voltages, especially at lower currents.

I was asking you since you already had it in a simulator. Maybe the voltage overshoot will be acceptable with an output capacitor added and faster compensation.

The overshoot is worse, at lower voltage settings. Adding some anti-slew diodes, along with the associated feedback network helps.

 PSU Instr Amp.asc (4.85 kB - downloaded 50 times.)

Here's what it looks like, with the output set to 5V, without R7, R8, D3 & D4.


And with R7, R8, D3 & D4.


Note, I set the current limit to 1A, as that's what the original poster's schematic does.

[xavier60]

I wonder if  Kleinstein idea will work in this topology, C2 gets connected to the ORing node rather than to the CV op-amp's output.
The mod made a big improvement to my design but it's the current sourcing type.
With C2 connected to the ORing node the CV op-amp will immediately get miller feedback as soon as the overload is removed allowing the output voltage to rise.
The mod will also cause a large negative going transition at the CV op-amp's Inverting input as the CC op-amp pulls down.
There could be other problems that I'm not seeing yet.

[Zero999]

I wonder if  Kleinstein idea will work in this topology, C2 gets connected to the ORing node rather than to the CV op-amp's output.
The mod made a big improvement to my design but it's the current sourcing type.
With C2 connected to the ORing node the CV op-amp will immediately get miller feedback as soon as the overload is removed allowing the output voltage to rise.
The mod will also cause a large negative going transition at the CV op-amp's Inverting input as the CC op-amp pulls down.
There could be other problems that I'm not seeing yet.

Oh I missed that in the other thread. That's the trouble when there are so many posts. It's difficult to read all of them in detail.

 PSU Instr Amp.asc (5.23 kB - downloaded 39 times.)

Yes that works quite well. I was a bit worried about oscillation, but I also plotted the output of the op-amp and it's better than I thought it would be.