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| 0.13x vs 1.0x gain op amp regulated power supply - fail |
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| xavier60:
--- Quote from: HendriXML on February 14, 2019, 01:52:35 pm ---One difference in the proposed schematic is that the capacitor is now sourced via R5. So a sudden increase in the supply voltage, might pull on the gate wouldn’t it? A phenomenon which has to be regulated, and might have effects on the output. --- End quote --- Yes, fluctuations of the input voltage will disturb the regulation. With the so called "floating type" regulator topology, all of the control circuitry is referenced to the MOSFET's Source which is also the positive output terminal. But it requires the extra floating rails to power the control circuitry. |
| HendriXML:
--- Quote from: xavier60 on February 14, 2019, 02:09:48 pm --- --- Quote from: HendriXML on February 14, 2019, 01:52:35 pm ---One difference in the proposed schematic is that the capacitor is now sourced via R5. So a sudden increase in the supply voltage, might pull on the gate wouldn’t it? A phenomenon which has to be regulated, and might have effects on the output. --- End quote --- Yes, fluctuations of the input voltage will disturb the regulation. With the so called "floating type" regulator topology, all of the control circuitry is referenced to the MOSFET's Source which is also the positive output terminal. But it requires the extra floating rails to power the control circuitry. --- End quote --- This all pulls a bit hard on me brain, ha ha. One possitive aspect of the initial schematic might thus well be that the “offset” is more tied to the ground/source. |
| xavier60:
--- Quote from: HendriXML on February 14, 2019, 02:23:48 pm --- --- Quote from: xavier60 on February 14, 2019, 02:09:48 pm --- --- Quote from: HendriXML on February 14, 2019, 01:52:35 pm ---One difference in the proposed schematic is that the capacitor is now sourced via R5. So a sudden increase in the supply voltage, might pull on the gate wouldn’t it? A phenomenon which has to be regulated, and might have effects on the output. --- End quote --- Yes, fluctuations of the input voltage will disturb the regulation. With the so called "floating type" regulator topology, all of the control circuitry is referenced to the MOSFET's Source which is also the positive output terminal. But it requires the extra floating rails to power the control circuitry. --- End quote --- This all pulls a bit hard on me brain, ha ha. One possitive aspect of the initial schematic might thus well be that the “offset” is more tied to the ground/source. --- End quote --- That is a bit tricky to nut out. I often see in high performance supplies a conventional 4 resistor balanced amplifier to sense the rail voltage and scale it down. This scaled down voltage and reference voltage is fed into another op-amp functioning as the error amplifier. All of this can be referenced to the MOSFET's Source pin. I hope I have that right. |
| xavier60:
Also, the op-amps won't have to be powered at the full input voltage. The balanced amplifier would need to have near perfect CMRR to prevent input voltage variations affecting regulation voltage. |
| HendriXML:
--- Quote from: Kleinstein on February 13, 2019, 03:58:38 pm ---The MOSFET is also rather nonlinear and will respond stronger at high current. So the response is to be expected very slow at low current and may be acceptable (and possibly to fast resulting in oscillation) at high current. --- End quote --- This is something I'm tried to find out in the supplied thread and if I'm not mistaken (maybe someone is willing to verify that?) more amplification is needed at higher currents. The Mosfet becomes more sensitive, but the voltage (source-drain) raise/amp decreases faster. I will test the initial circuit with minimal gain using the graph: 1/4 from the diff. amplifier * 1/2 from the divider. 1/8 should still work. Maybe then we'll also see a larger voltage drop at a sudden load. |
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