| Electronics > Projects, Designs, and Technical Stuff |
| SMPS for vacuum tube power amplifiers.(status: back at it) |
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| SK_Caterpilar_SK:
Alright this is how far i got. I dont have aux windings so I had no idea how to power the chip, so I decided to go with a pass tipe regulator, after all the worst it can get is 2W loss (5mA limited current draw). there will be a mains filter before the rectified, just externally. I have not chosen values for everything yet. There are two mosfets on the schematic (so I can either use TO247 or TO220). I dont have a snubber network yet. I dont know how to make one at all. And if its at all necessary. (Fsw 100kHz, VinDC 100V-400V and Ipk=2.55A) I have utilised all my dirty tricks there in the feedback to not burn the 431 in the instant the PSU is turned on. |
| SK_Caterpilar_SK:
Also I have seen in many SMPS designs capacitors going from primary ground to the secondary ground (small capacitance high voltage rating cermaic caps). Rumor says its for noise reduction but I dont really know if it will be necessary. I can add them onto the PCB and during testing I can just leave try them and if it wont work nicely then not populate the places. I just dont know what capacitances to look for, and if its even necessary. |
| T3sl4co1l:
Snubber and Y-cap (GND-GND) depend on transformer characteristics. Ideally, a shielded transmission line transformer could be made, giving very little common mode noise, and a modest amount of leakage which may be tolerable without a snubber. This is not easily made, however: personally, I'd sit down and take about an hour to design such a thing, checking against available cores and bobbins to see how much winding area and wire length is possible, and therefore what impedance, and how much leakage inductance, I can get. But if you're just putting windings on a core, count on needing both, and common mode chokes. Typical snubber is just the drain pin into a diode into a capacitor to ground. The cap is relatively large (>= 10n?), so that the peak voltage gets clamped by it. This "boost" voltage is discharged into the DC+ supply with a power resistor. The capacitor can be DC+ referenced, if the DC+ bypass is nearby. This is often seen in commercial designs, since it's easier to lay out (the R and C are simply in parallel). Note that you want a TLVH431 or the like -- lower minimum current. Tim |
| mrjoda:
For bobbins and cores, check the semic trade (semic.cz) it is the best distributor for these things as i know in our countries. |
| SK_Caterpilar_SK:
Thank you Tim for your reply. No the transformer is bought from coilcraft. Part number is HA4060. So far I did not make my own. Its been pre made for a different but similar purpose. The specs of the transformer are here. I will be slightly overdriving the transformer (2.5A Ipk instead of 2A) https://www.coilcraft.com/pdfs/ha4060.pdf Im not looking forward to wind my own transformers. I rather quote Coilcraft for something custom or the local manufacturer.. Do I need a snubber network at all and if yes how do I design one ? |
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