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| High Voltage Bench Power Supply Design |
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| Doctorandus_P:
With High voltages Power dissipation increases rapidly with a bit of current, but of course you already know that. I was also thinking about building some kind of high voltage supply. My first thoughts are around using an LM2587 Fly-back converter and a transformer of an old PC power supply in "reverse". For a higher output voltage you can put the 230Vac windings of 2 transformers in series. It should also be almost trivial to add a few tranistors (or optocoupler) and a Zener that throttles the LM2587 down as soon as the output voltage is 10V or so higher than the output of the lineair regulator at the end. |
| Wolfgang:
--- Quote from: BravoV on February 06, 2019, 12:02:09 pm --- --- Quote from: Wolfgang on February 06, 2019, 09:36:56 am ---Hi, I have build this but as expected it is very slow. You could speed this up by replacing the photcell coupler by a small transformer-based supply plus a normal optocoupler. This can also drive more current then. Furthermore, the BU208A could be replaced by a linear MOSFET, now available up to 2.5kV. --- End quote --- Mind share your circuit in schematic, as I have difficulty to visualize it. Btw, you said very slow, do you mean the regulation ? How slow ? --- End quote --- Give me some time, I'll post a schematics Wolfgang |
| H713:
Little update: The project is not dead, I've just been extremely busy with work, school, and many other projects. Attached is how I plan to do current limiting in some form or another. The clean and elegant way of doing this would be to connect R1 to the output of the LR8 and use the series pass transistors to do current limiting as well. The belt-and-suspenders approach is to stick this mess in series with the rest of the circuit. The downside, of course, is that I use at least two (probably three) additional (costly) transistors. It is probably a safer approach, however. The one other issue I'm working at is the load switch, and how to switch voltages in excess of 500V. Something tells me that you're not supposed to use a standard 250V toggle switch for this. |
| H713:
Alright, the design has seen a revision. The LR8 is a great little device, and would be fine for most applications, but I want more than 450V. In addition to that, I think I can learn a lot more by going without it. Here is what I came up with. Not a complicated circuit, and I'm sure by no means unique. Sorry the schematic is such a mess, it is still a work in progress. Transformer tap switching will be accomplished using a 120:200 transformer with a voltage doubler. A relay will be used to switch between the full and 50% voltage points (convenient aspect of a doubler). With a beefy transformer, likely a .5 kVA "general purpose" control transformer (Tek transformer was commandeered for another project) and large caps, I can get decent regulation out of this. The switching of "taps" will be done on another PCB that is the control board, which will monitor temperature of the heatsink and adjust fan speed accordingly, handle "tap" switching based on output voltage and deal with "fault" conditions (pass element short, over-temperature, insect infestation, etc). One thing that I personally like about this is that if the pot wiper were to go open, the power supply would drop to its lowest output setting, rather than dumping the full 500V into the load. With this design, I plan to have the power supply adjustable from about 15 to 525 volts- good enough for most tubes. Adjustable current limiting is a nice feature, but I don't feel the need for it to be very precise. As such, I'm just going to use a 5 ohm rheostat for R11. |
| T3sl4co1l:
Source, not drain resistors! Mind that 47k pullup into huge gate capacitance will give quite low slew rate. So low you may have problems with ripple rejection. I don't get the 24V supply just for the opamp. Why does it need to be regulated? Why does it need to be so high? It could be anywhere from 3.3V (use precision 1.24-2.5V reference; downside, Vbe of level shifter is a larger fraction of Vout) to 9V (pretty much everything as shown, resistors adjusted as needed). Supply can be an unregulated DC wallwart, or a tiny SMPS, or maybe even something obscure since so little current is needed (e.g., coupling caps from mains, into a rectifier and shunt regulator, load side grounded -- a few mA won't trip an RCD/GFCI). Not that 7824s are expensive or anything, but on that note, a shunt regulator with a pair of 6.3V diodes in series would get you a nice pre-reference for low noise and ripple, without the bulk of a regulator and associated caps. Tim |
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