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| Adjustable Voltage Supply: Schematic Concerns |
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| LoveLaika:
--- Quote from: xavier60 on May 10, 2020, 02:49:24 am --- --- Quote from: LoveLaika on May 10, 2020, 02:16:00 am ---So, with a capacitor by itself, it'd be an integrator. A capacitor/resistor parallel together would form an LPF. That's an interesting thought. I'll give that a try. Thanks for the comments. I'm learning more issues with my circuit as I read responses along with some ideas that I'd like to try out. --- End quote --- A capacitor by itself forming a Miller Integrator works with linear designs, then it occurred to me that extra lag caused by the inductor would likely cause it to make things worse. Putting a resistor in series with the capacitor allows some proportion response, reducing lag. If the CC loop is really unstable and oscillating, the resulting audible squealing could be annoying. --- End quote --- Then, perhaps a different method might be worth looking into for current limiting. I found a video online showcasing the LMP8646 current sensing amplifier, and using that in place of the TLC272 seems to work pretty well. There's a lot less ringing at the feedback node, and it's more suited for stuff like this. |
| xavier60:
One possible way of looking at it is, assuming that the output is shorted to ground, the CC loop is effectively regulating voltage across the CS resistor. The voltage drop across the CS resistor needs to be transferred to the FB pin without much gain applied. The DC to low frequency gain can be high without causing a problem. |
| LoveLaika:
--- Quote from: xavier60 on May 12, 2020, 09:27:52 am ---One possible way of looking at it is, assuming that the output is shorted to ground, the CC loop is effectively regulating voltage across the CS resistor. The voltage drop across the CS resistor needs to be transferred to the FB pin without much gain applied. The DC to low frequency gain can be high without causing a problem. --- End quote --- I have to change my design around due to issues with the output connection. The positive and negative outputs need a shared return to GND on the board, so the way I have current limiting now, with the sense resistor and IC, may not work. I was thinking of reworking it by adding a 30k-pot (if I can find one) to the Iadj pins and limit the current through the inductor. Radj at that pin = 37125/(Peak Switch Current), and the peak switch current needs to be approx. 1.5x the max load current, so I could limit it that way as well. |
| LoveLaika:
If you don't mind me asking, you have any suggestions as to some alternatives that I can consider? Considering the type of output connection I want, with a single GND point, I'm looking into new ways of running my negative circuit. Take this with the LT1074. Pretty simple, lots of documentation, but if I want to put in a sense resistor for measuring current, say to use as a warning indicator, how can I fold it into my circuit without affecting the output voltage? |
| LoveLaika:
Considering what one user said, the needs for my connection to have one single GND pin makes my circuit pretty much unusable. I'm looking into new methods, such as with the LT1074. It seems to work well (and the model works in LTspice), but if I want to add a sense resistor, how can I incorporate it into my circuit without affecting the voltage? |
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