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| Preregulation of a linear bench PSU |
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--- Quote from: not1xor1 on December 29, 2018, 08:55:27 am ---These last two screenshots show the peak current and voltage spike when switching from low to high voltage. The simulation has been run with a huge 47.000µF capacitor and a load of 10Amps. --- End quote --- Really nice circuit i'll try it, i have already on hand some low rdson Pmos I was a little worried about the peak current 200A but then i saw that the measurments were done with 47000uf @ 10 amps:-DD |
| Atom:
--- Quote from: blackdog on December 29, 2018, 04:01:16 pm --- If you only need one switchpoint than take a look at this schematic, it uses a Schottky diode and a PowerMOSfet. www.bramcam.nl/Diversen/CO-2016-PSU.pdf --- End quote --- thanks i'll try also this out :-+ |
| Kleinstein:
--- Quote from: blackdog on December 29, 2018, 04:01:16 pm ---Hi, If you only need one switchpoint than take a look at this schematic, it uses a Schottky diode and a PowerMOSfet. www.bramcam.nl/Diversen/CO-2016-PSU.pdf ... --- End quote --- That version of tap switching looks nice and simple. The nice point with the diode is that, there can be no cross conduction. The voltage loss only happens at in the lower tap case, where is does not hurt much. The relatively slow turn on of the MOSFET limits peak currents, when going from the center tap to the full voltage. There would be some heat loss at the MOSFET, but not that much (e.g. comparable to 1/4 the energy in the filter caps) and more of a transient mode. Moving the switching from low to high tap close to the zero crossing could further reduce the current peak a little. |
| not1xor1:
--- Quote from: Kleinstein on December 30, 2018, 10:50:40 am ---That version of tap switching looks nice and simple. The nice point with the diode is that, there can be no cross conduction. The voltage loss only happens at in the lower tap case, where is does not hurt much. The relatively slow turn on of the MOSFET limits peak currents, when going from the center tap to the full voltage. There would be some heat loss at the MOSFET, but not that much (e.g. comparable to 1/4 the energy in the filter caps) and more of a transient mode. Moving the switching from low to high tap close to the zero crossing could further reduce the current peak a little. --- End quote --- I agree that Blackdog's circuit is much simpler (I made something even simpler as it was for regulation on the negative rail). When converting from AC to DC you have a fixed voltage loss (max peak-to-peak ripple voltage + max dropout of regulator) plus diode bridge and transformer loss. In the case of center tap transformer the diode bridge and transformer losses are halved, but the other aren't so saving that fraction of volt wouldn't be so bad. :D In any case such a complicated circuit is obviously an overkill for a single tap. I designed that just for the puzzle solving fun. :) But in future I would start from there to replace the triacs in the HP 3 taps switching design. |
| Kevin.D:
A full wave voltage doubler could be added on to that to give two extra extended ranges. There is one disadvantage I can see though as it's halving the output capacitance (since 2 caps in series) on the lower voltage (higher current) ranges where its needed most. Notice on the third range how the top caps gets charged upto double the voltage of the bottom cap to get us the third range (sw1 closed sw2 open). The available outputs currents and voltages I give on the schematic are what should be theoretically available from the transformer and don't include rectification losses. Happy New Year . |
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