For example transformer of 300vac-0 to get output vary between 275vdc-330vdc
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Or-
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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I already have 320-0-320vac but i need only 320-345vdc output what value of 33K 47K to be replaced for
1. 320Vdc
2. 345vdc
Thx
1. 320Vdc
2. 345vdc
Thx
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
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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