| Electronics > Projects, Designs, and Technical Stuff |
| Preregulation of a linear bench PSU |
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| BravoV:
Not sure if this is suitable, another design idea posted while ago here on taps switcher -> HERE |
| Kleinstein:
--- Quote from: Atom on December 25, 2018, 07:15:59 pm --- --- Quote from: Kleinstein on December 25, 2018, 06:44:40 pm ---There is slight chance the Mosfet for the common pin is not turning off fast enough. So there could be transient current flow through both MOSFETs, especially of the grid voltage is not a nice smooth sine, but with sharper slopes. So it might be a good idea to use a diode instead of the MOSFET at the COM pin. --- End quote --- so the problem with the circuit is that there isn't enough dead time and all the 2 mosfet could be conducting ad the same time shorting out COM with AC2 (and maybe themselves since there is a lot of current passing in a short)? is my understanding correct? --- End quote --- Yes having both MOSFETs turned on at the same time would be the thing I fear could happen. Maybe not with a clear sine, but possible with a distorted grid voltage. I would not take the chances and use a diode instead of the one of the MOSFETs. --- Quote from: BravoV on December 25, 2018, 07:16:22 pm ---Not sure if this is suitable, another design idea posted while ago here on taps switcher -> HERE --- End quote --- The the link shows a linear turn over with MOSFETs more multiple taps, similar to the linear version I suggested earlier for 2 taps with a BJT based circuit. It's different in the details but similar in the principle. It is especially suitable for the regulator with floating supply, as the drive of the gates / bases is easy in this case (fixed relative to auxiliary voltage). |
| Atom:
--- Quote from: BravoV on December 25, 2018, 07:16:22 pm ---Not sure if this is suitable, another design idea posted while ago here on taps switcher -> HERE --- End quote --- while i find the circuit pretty intresting i think it isn't worth it mainly because i would need to buy other bulk capacitor, increasing already the size and cost of this psu. i think i'm going use the mos switching circuit. the losses on the diode if i use one instead of the mosfet are Vd*I right so 0.7*8Amp max = 5.6W that's quite a bit of power |
| Kleinstein:
--- Quote from: Atom on December 25, 2018, 10:35:04 pm --- --- Quote from: BravoV on December 25, 2018, 07:16:22 pm ---Not sure if this is suitable, another design idea posted while ago here on taps switcher -> HERE --- End quote --- while i find the circuit pretty intresting i think it isn't worth it mainly because i would need to buy other bulk capacitor, increasing already the size and cost of this psu. i think i'm going use the mos switching circuit. the losses on the diode if i use one instead of the mosfet are Vd*I right so 0.7*8Amp max = 5.6W that's quite a bit of power --- End quote --- The loss at the output transistor is still much higher, more like 10 V drop on average. If really needed one could have a Schottky diode - though not that easy with high peak current. |
| Atom:
Well sure the losses on the power transistor are much higher ..higher tap 40 v switching at 13v max current is 8 Amps 27×8 = 216 W well yeah thas quite a bit of power in fact i was thinking of limiting the current at 5/6 amps in the higher tap mode. |
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