300V AC/DC variable power supply

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300V AC/DC variable power supply project by Dilshan Jayakody

This 300V AC/DC variable PSU is designed for our vacuum-tube, MOSFET and some IGBT related experiments. This PSU consist with 0-300V Variac (variable auto-transformer), 700VA isolation transformer, which is described in previous blog post and high voltage AC-DC converter. Because of the size and weight of these equipment’s we build this PSU as three separate units.
This PSU is capable to supply 20V – 300V 2.3A (max.) output in either AC or DC form. This PSU use high voltage and because of that, all the proper construction and precautions are necessary to take. Improper wiring or construction may leads to lethal electrical shock and/or fire. If you are not familiar with high-voltage practices do not attempt this project at home.

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2 Comments

  1. Hm, this is an “unregulated” power supply. i.e. barely more than a transformer and a bridge rectifier. Last time I saw an unregulated supply was in the 1990’s. Anyway..

    By the way, the ripple voltage is large – the output rail capacitance is way too insufficient for 2A.

    The guy states on his blog:
    “This PSU use high voltage and because of that, all the proper construction and precautions are necessary to take. Improper wiring or construction may leads to lethal electrical shock and/or fire. If you are not familiar with high-voltage practices do not attempt this project at home.”

    And yet, according to his circuit diagram ( http://elect.wikispaces.com/file/view/300vaPSU.PDF/500831132/300vaPSU.PDF ) he has placed the fuse after the switch!

    Then, he goes from the Variac to his isolation transformer using the 4mm type plugs (like on multimeters) in his photo (that’s right – plugs).

    Of course, earthing is non-existent too.
    The mind boggles.

  2. Depending on the Earthing system used in that country, it may or may not make a difference whether the fuse is before or after the switch, at least in terms of getting a shock in the situation where a fuse blows and somebody plays with it thinking it is off. Some people also argue that having the fuseholder after the switch is safer in case they are those horrid fuse holders that expose the conductors, though the same comment above applies to that too.

    If it were me, yes I’d have it before the switch and yes using Banana plugs for any sort of high voltage work is absolutely nuts.

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