I want to make power supply from 220 V AC to 300 V DC variable/adjustable? Answered

A Variac is NOT MAINS ISOLATED, and therefore very dangerous unless appropriate precautions are taken.

Then just connect its output to a isolation transformer. besides, if proper precautions (common sense) are taken it will be fine.

Then make sure you mention it, when you tell people to use things like variacs.

Why does main isolation matter if it is set on a lower voltage? besides, dealing with anything over 50 volts is dangerous (unless it is current limited).

What's the voltage ? Referred to ground ? And no, anything that can drive more than 20mA through your heart is potentially fatal - less if you're old/young/ill. Voltage has nothing to do with it, in the sense of the level of it being safe or not. The 20,000V shock I receive in winter, walking over the carpet is not fatal.

voltage dictates how much current will flow (Ohms law). a 12 lead car battery can pish out thousands of amps, but they dont kill because the voltage is not high enough to cause a significant current through the body. I also stated "current limited". I mean ~10 mA current limited. I would know.because I mess around a lot with high voltage.

WHAT??? I think someone should step away from the keyboard.

Less than 9V has been know to kill, less than 10mA has been known to kill - that's why earth leakage limits on medical equipment are 1/10th of those for other types.

RESISTANCE controls current flow. (Ohms Law)

A car battery can't push ANY current into an infinite resistance.

You may mess around a lot with high voltage, you appear to know dangerously little about what it is and when it can cause damage.

9 volts directly across the heart will probably cause enough current to flow. yes, I know. Ohms law is a basic equation that mathematically demonstrates how current, voltage, and resistance are related.

Now imagine that 9V superimposed on 110.

Why wouldn't you connect a isolation transformer to the variac input ?

I never said I wouldn't connect it?

I was asking you,  what about putting the isolation transformer  on the mains side
of the variac  instead of the output ?

" Why wouldn't you connect a isolation transformer to the variac input ? "

Being appropriate ;-)

I was only trying to determine if this young man has enough knowledge to avoid
being hurt by the very energy he wants our help to control.

He does not appear to have an understanding of isolation transformer size relating to current.
Let alone the concept of a switcher.

It is almost as if a circuit is going to provide the answers to everything.

May be we should simply show a TR unit with a variac.

A

220 V AC to 300 V DC and current may be 1 A or any other value, 300 V is important

Yes we get that. You want to convert 220VAC to a max of 300VDC. But what adjustment range do you want for the DC side. 0V-300V, 5V-300V,3V-300V, ect. Also why do you need an adjustable supply that can offer up to 300VDC but only up to 1A?

0 - 300 V, for my FYP

FYP = five year plan ?

300V regulated, 300W PSU.
Adjustable from what to what ?

0 - 300 V.

How much electronics experience, and working at high voltage do you have.
Do you need current limiting at 1A ?

I m a student and want this supply for my FYP, current may be less than 1 A but 300 V is important may be 1.2 - 300 V.

Ah, the idea of "FYP" is that its YOUR work. We'll assist, we won't DO your project for you.

This would make a great switch mode PSU project, but you could just about do it in a linear one, though in some conditions, you will have huge power dissipation in the pass-bank.