DC-DC Converter: 12VDC to 250VDC 25ma

Line output transformer core from an old TV?

Well yes but I did mention miniture like a stomp pedal that uses a tube I need it compact. No old TV's around here anyway all LCD and Plasma. LOL

What type of converter are you building?

Flyback, Forward, Isolated, Non-isolated boost?

What frequency are you switching at?

Do you have any minimum efficiency requirements?

DC-DC is preferred 12.6 in 250VDC out or

DC-AC 12.6 in AC out to be rectified to DC 250VDC.

Need to be compact and as long as I have duty cycle control to saturate the core this is a lot of you efficiency and dv/dt of the MOSFET. Fast HV switch. I will just step-up the core more turns if I have to.

But the main problem is finding a good small core to wind a step-up transformer! This is the primary issue. And I gave the part number now obsolete I have a circuit that uses this transformer ETD29-3C90 by ON electronic.

Just use a stock 10 VA 240:10 VAC step down transformer in reverse. It will give you roughly 240 -260 VDC when rectified and filtered.

A 5 VA 120:5 VAC unit running at a higher frequency can also step up 12 volts to 250 volts DC as well and hold the higher wattage without problems too!

Yes I have done this before with a small audio 8 ohm transformer and got over 100V out. I would prefer to make my own custom small transformer and found some ferrite cores on eBay pretty cheap and just wind my own. I need it to be small also. Thanks best answer so far.

This article in EDN describes a 12V-to-180V, transformerless, regulated DC-to-DC converter which you can build using common, off-the-shelf parts. The converter consists of an inverter and a voltage multiplier, and the multiplier can easily be extended produce higher output voltages, as required. Output-current capability (up to 1000 mA) is well in excess of 25 mA, should you need it.

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You may want to search for strobe light parts. Some of the electronics hobby pages give sources for both transformers and trigger coils, that can get you up to the kV range with very small amperage...

Disclaimer: I don't know any thing about this sort of thing.

Is this any use:-

http://www.tscinternational.com/mainferr.html

About half way down the left hand side under TSC core parameters, there is a drop down menu: if you choose ETD core data you get a spread sheet which includes an ETD29 with the same dimensions as the part you're looking for. (I realise there are other important parts of the spec. but I don't understand them )

The circuit you are referring to appeared long time back in the Australian magazine siliconchip.

The core for the xfmr is available from Farnell, they sell both Ferroxcube and Epcos cores. Farnell India sells it for 10$ equivalent which is an atrociously high amount considering the fact that we get new power transformers for 75VA for $4 equivalent in Bangalore.

It is not a very critical design, you could pick up any of the junk PC SMPS module and salvage the ferrite core transformer from it. Just wind the no. of turns as specified in the article, you will be in business.

good luck

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