How to generate 250VDC from 12VDC input

mozwell · Post by **mozwell** » 31 Jan 2011, 23:32

Here's something i came across a while ago & thought i would share it here.
Its from an australian magazine, and is an easy way to generate 250VDC from a 12VDC input supply.
I hope its of some use.....

I dont have pcb's available. It should be easy enough to prototype though.

cheers Andrew

toneman · Post by **toneman** » 01 Feb 2011, 00:51

nice!

DrNomis · Post by **DrNomis** » 01 Feb 2011, 11:27

There's another way to generate 250V DC,all you need is a 12V AC plugpack,a 240VAC to 12.6V AC@150mA transformer,1X DC socket,1X DC Plug to fit socket,4X 1N4007 Power Diodes,and a 47uF/450V DC capacitor....

Method:

First,solder the DC Plug onto the 12V AC Plugpack's lead,next,build up the circuit shown in the schematic below,solder the 240V AC primary leads of the 240VAC to 12.6V @150mA Transformer,to the AC input of the bridge rectifier,then solder the 12.6VAC @150mA secondary leads to the DC socket,insert the DC Plug into it's socket,plug the plugpack into a wall socket and switch on,you should see about 240V-300V DC across the 47uF/450V DC Capacitor.

Yes,what we are doing is using the transformer backwards,it steps up and converts 12V AC to 240V-300V DC

toneman · Post by **toneman** » 01 Feb 2011, 14:03

this is an Electro Harmonix technique.
EH uses torriod xfmrs, but a xfrmr is a xfmr.

I'm just like micro-miniture switchers

Perferably, ones that use the ol' 555.

mozwell · Post by **mozwell** » 02 Feb 2011, 22:19

Of course, if you have an AC input available, then the backwards transformer is an easy way of getting a HV supply.
If you only have DC available, then the switchmode approach is a simple method to get the HV supply.
I have updated the pdf, i have included an inductor design which shoudl be ok for commonly available pot cores here in Australia.

I hope this is of use to people.

KMG · Post by **KMG** » 03 Feb 2011, 12:53

I use UC3843 & standard Sumida power inductors to generate 250VDC from 12VDC

250dcdcSch.pdf: (23.89 KiB) Downloaded 330 times

mozwell · Post by **mozwell** » 04 Feb 2011, 00:43

Nice solution KMG
I have used 3843 for years in small flyback supplies up to 75W.
the benefit of your circuit over the one in the australian magazine is that you have a mosfet current limit, and not having to wind a special inductor is the best part of your design.
All the voltage boost is done with the 100uH inductor, and the 1mH inductor is an extra filter for the DC supply, whereas the circuit from the australian magazine used the tap on the inductor to keep the mosfet drain voltage lower, with the tapped inductor worked like an auto-transformer.

Both solutions will work fine. I dont have IRF730, but i do have IRF840, so i will use the higher voltageg mosfet when i build up your supply

Now everyone can have a simple 250V low current supply from a 12VDC input, with low cost, off the shelf parts.... as long as people find this thread, that is

In Australia suitable inductors would be Altronics L6522 or L6222 for the 100uH, and 2x L6230 in series for the 1mH inductor

DrNomis · Post by **DrNomis** » 04 Feb 2011, 09:35

I can see the advantages of the Switchmode Power Supply method,you can then power the tube filaments with DC,rather than AC,which means lower hum levels,I'm thinking of building a Matchless Hotbox and have been thinking of ways to generate the HT needed to power it,the enclosure I want to use is a bit limited in space,so I was intregued by the SMPS design....

spherical · Post by **spherical** » 13 Jun 2012, 00:10

KMG wrote:I use UC3843 & standard Sumida power inductors to generate 250VDC from 12VDC
250dcdcSch.pdf

This is great! How much current will this supply?