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Old 14th March 2014, 08:43 PM   #51
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Just for grins, I ginned up a simulation using a OPA541 power opamp as a series-pass regulator that can both source and sink current. It needed relatively few parts to get going, and its response to a 10kHz sine current load was clean. It may be that the key to cleanliness is the ability to source and sink current. I'll find out when I compare that solution to a conventional opamp-based regulartor that can only source current.
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Old 18th March 2014, 12:40 AM   #52
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Last night, I built up a grubby perf-board prototype of the series-pass regulator shown in post #17 of this thread, though without C4/R14 and C3/R13. I also used an IRF9610 rather than an IRF9520 for M2.

The supply regulated nicely at around 30.2 VDC for a 40 VDC input. At work today, I loaded it with one of our Kikusui electronic loads and gave it a dynamic load step, while monitoring the output voltage with an AC coupled 1X probe. The output response to the load step is very well-behaved. You can't see the output noise of the power supply over the self noise of the digital scope (the trace with power supply is no thicker than the thickness with no supply connected). The supply shows a ~0.8mV excursion for a 100ma load step, which works out to 8 milliohm output impedance. If I changed my monitoring point to near where the output voltage is actually sensed by the regulator, I may be able to better that.
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Last edited by wrenchone; 18th March 2014 at 12:53 AM.
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Old 18th March 2014, 09:12 PM   #53
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For grins, here is a regulator based on an OPA541 power opamp. I'd expect similar behavior out of an OPA549. This is quite possibly the only way I'd let one of these things near my audio gear... At any rate, the parts count is not too extreme, and it behaves itself, though more tweaking of the output capacitance may be in order. The error associated with the current sense node doesn't appear to be affecting the operation.
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Old 18th March 2014, 09:17 PM   #54
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THe output impedance of the regulator as presented is nothing particularly shecial (~4.5 milliohms). The response to a sine wave current source load (20 mA with 0.1A DC bias) is pretty pure, no doubt helped along by the fact that the opamp is running Class A, and the fact that there's all that open loop gain to be had...
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Old 19th March 2014, 08:53 PM   #55
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Attached is a repeat of measurements of the regulator shown in post #52. As before, the regulator was tested using a Kikusui electronic load, with a load step of 50mA - 150mA - 50ma. This time the voltage sensing point was shited to directly across the voltage divider network for the error amp to get a better sense of the native output impedance of the regulaotr without intervening voltage drops.

As can be seen, the changed sense position greatly reduces the voltage shift for the same magnitude of current step. The output voltage excursion is 0.2-0.3 mV for a 100mA load step - this calculates out as 2 to 3 milliohms output impedance. Of course you'll only see that lower output impedance if your load is hooked up right at the sense point. Anything farther away will also have the intervening impedance of the connecting traces/wires added to the intrinsic output impedance of the regulator.

The moral of the story is that you put your nastiest load (like a line amp) closest to the regulator sense point, and the less difficult loads farther away.
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