Dear jonnybgood
Again Hi
As i told you , we have many many different way for current controlling . but this way is usual and very good , and when the out put voltage is short circuit , the voltage can not increase ( remember that this circuit called hiccup current limiter , and at one time the current limiter , do it's duty , and at the other time , the voltage feed back will do it's duty .
BTW : i built 25A power supply with this way about 2 years ago.
Best Wishes
Goldsmith
In fact I figured out that I was putting the current sense resistor to the emitter not to ground.... I will try with it connected to ground today
thanks for now.
---------- Post added at 11:31 ---------- Previous post was at 09:53 ----------
With current limit resistor, the voltage at the output terminals fall below 9V (0.1 Ohms * 2.7Amps = 0.27V drop). I know that the op amp is trying to keep a 9V across the load and current sense resistor in series not the load only. Since the feedback is from a voltage divider from emmitter to ground. Can I take feedback only from the output with respect to current sensing resistor instead of directly to ground?
As you've noticed, sensing current in the ground path can cause some issues, but they are generally solvable.
For the issue described above, you can either use a differential error amplifier to sense only the voltage across the load and not the current sense resistor. Another possibility is to reference all the circuitry to the other side of the current sense resistor (the negative terminal of the load), essentially making it the actual "ground" of your circuit.
Another issue with ground current sensing is that if you want to connect other supplies common to its output, you must be careful to connect them at the negative load terminal, on the output side of the current sense resistor. Otherwise you are likely to cause severe issues with the current sensing, or get errors in the output voltage. Also when doing this you should make sure that the input supply voltages to each regulator are isolated from each other, so that they do not short out the current sense resistors.
Hello my friend
there is the better way for voltage regulation available that called LDO Method ( low drop out) . the other advantage of LDO is that you can control the output voltage from zero up to input voltage ( suppose that your input is about 90 v and the supply of the control op amp is about 15 v , with LDO you can control it from 0 up to 90 volt simply and your op amp don't need 90 volt as supply voltage !!!!)
Here you can see simple LDO : View attachment 68169
you can change the out put voltage with changing the v4.
Good luck
Goldsmith
Dear Jonny
Hi
I can't understand that what is your problem clearly ! can you describe your new problem , please?
All The best
Goldsmith
Now the input of the 7805 will vary from 17V to about 12.5V once the psu is loaded with max load. This change in input of the voltage regulator is causing the output from 5V to drift by 20-25mV. This is causing the noninverting input to drop also causing a nonlinear current limiting over different loads. I need a more precise voltage reference than the 78L05, this can be anywhere from 2V -5V. What are some common voltage precision reference that are cheep. If it drifts by a millivolt it is oki. I will power it by the same regulator.
The voltage across D2 is a 5.1 volt but very very constant
View attachment 68212
Respectfully
Goldsmith
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