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The Variable High Voltage Power Supply 0-300V | ElecCircuit.com
I have built several along those lines for use in old radio receivers or for testing HV circuits using mosfets exactly like that one .
Personally --and this is my personal practical opinion too many BJT high voltage circuits are not as robust as mosfet ones due to breakdown/sc in BJT pass devices .
The Variable High Voltage Power Supply 0-300V | ElecCircuit.com
I have built several along those lines for use in old radio receivers or for testing HV circuits using mosfets exactly like that one .
Personally --and this is my personal practical opinion too many BJT high voltage circuits are not as robust as mosfet ones due to breakdown/sc in BJT pass devices .
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The issue is that while pots used for the 249R or (33k+47K) would make the voltage variable, this circuit uses large resistors and a normal pot would overheat. Also, min and max voltages may not be ideal. These circuits use odd parts that are not necessary in this application. LV (Elvee) has a post on DIYA for a similar application that is a better design. A simpler circuit is not difficult but would not perform as well as LV's. Certainly you will want to work with a HV MOSFET because that allows high resistance pots and resistors that don't get hot.
https://www.diyaudio.com/forums/power-supplies/330193-elektr-true-voltage-lab-supply-truly-diy-friendly.html#post5606157
https://www.diyaudio.com/forums/power-supplies/330193-elektr-true-voltage-lab-supply-truly-diy-friendly.html#post5606157
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But the answer is in LD1086 datasheet (the same as for LM317):
Vout = 1.25× (R1/R2 + 1).
R2 = 249 R. You may increase this resistor value (up to 500-750 R) to increase proportionally R1 value, to lower power dissipation. This is ok if you have some small load (few mA) at its output. (For example, a 1 mA LED may be as such a load).
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This is not a regulator, but a cap multiplier. The output voltage will automagically rise or fall with the input voltage. You don't need to change anything.
Jan
Another schematic for Supernut
Mona
That's a rather nice schematic, to understand it better. The LND150 is a current source here. That sets the current through the zener. furthermore i would increase the divider current to about 2mA.
I would replace the IRF840 with :IXTH15N50L2 IXYS and use a big heatsink.
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I was thinking you need to buy a ready made power supply because an efficient variable supply means a switch-mode supply and clearly you are not into something that complicated. But searching Amazon, the only thing I found is a ~12V to 390V inverter which is not high power.
However an ad gave me the idea that what you need is a Variac, variable transformer, from which you can run a simple power supply with none of the problems that these circuit suffer from.
Amazon.com: YaeCCC Auto Voltage Transformer AC Variable Voltage Converter Transformer 110VAC Input, 0-130VAC (500W): Industrial & Scientific
However an ad gave me the idea that what you need is a Variac, variable transformer, from which you can run a simple power supply with none of the problems that these circuit suffer from.
Amazon.com: YaeCCC Auto Voltage Transformer AC Variable Voltage Converter Transformer 110VAC Input, 0-130VAC (500W): Industrial & Scientific
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