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| 0.13x vs 1.0x gain op amp regulated power supply - fail |
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| HendriXML:
--- Quote from: HendriXML on February 13, 2019, 06:13:21 pm ---The question I want to answer is what range it can regulate without significant drops. Somehow I think the integration of the ratio curve in the other post has a relation to it. My thoughts are if it’s less than 1 (or 0.5 because of the resistive divider), it’s okay. If its more, the reference capacitor needs to charge a bit further, so the output voltage will drop. --- End quote --- From the measurements done above this does not seem the case. That raises also the question about how important the raising of the ref voltage is. Or wether it is possible to drive the Mosfet with even lower "gain". To bad I've soldered the resistors down so that isn't just a quick check. The legs are also the traces...perfboard experimenting issue. |
| HendriXML:
I wanted to make sure that the constant current mode of the Siglent had no part in the voltage drop, so I did new measurements with the CC up to max (3.2 A) Resistor Siglent powersupply My circuit 5R1 2.08 V 0.60 V 6R8 1.90 V 0.50 V 10R 1.62 V 0.40 V 15R 1.36 V 0.30 V |
| xavier60:
It looks like you are using positive feedback to increase gain at DC and low frequencies? |
| HendriXML:
--- Quote from: xavier60 on February 14, 2019, 01:25:52 am ---It looks like you are using positive feedback to increase gain at DC and low frequencies? --- End quote --- Yes but with some delay. The idea is that it settles on a value so that a even a little effort of the “diff amp” has still some effect. To keep the volts/sec low. |
| xavier60:
An op-amp configured as a non-inverting amplifier with a feedback capacitor from the op-amp's output to inverting input will give the same result plus even more gain at DC. This will reduce the regulators steady state output voltage error to less than a millivolt if the layout is done right. BTW, your output stage is current sourcing into a capacitor. For the feedback loop to be stable in this situation, the error amplifier(op-amp) needs to have some proportional gain. An op-amp configured as mentioned above has a gain that can only drop to one at higher frequency. This is well suited. |
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