I'm looking for the best way to get from mains rectified 330V DC down to more manageable ~24-36V DC.

From what I know the most efficient way is to use a step down buck converter. But I'm having a hard time trying to find a part that will do the job. Any advice on what I could use?

Thanks in advance.

 

Hello,

I would play it safe.
Powers supplies directly powered from the mains are not allowed here.

Use a transformer from the mains to about 24 Volts.
Rectify that and buffer voltage and you will have about 33 Volts DC.

Bertus

 

That is the safest way to do it and I will probably go down that route.

So purely for my own interests/learning how would you go about doing it from 330V?

 

I'd use two transformers, considering that I have never seen a transformer that is rated for 330 volts. Put a 230 volt transformer primary in series with a 115 volt transformer primary. That would result in a primary design voltage of 345V.

Now consider that both primaries must have the same current because they are in series with each other. The 230 volt transformer must provide twice as much power as the 115 volt transformer, thus it must be rated for twice the voltage of the 115 volt transformer. Experience tells me that 12V and 24V are often used voltages, so I would buy a 115V to 12V transformer and a 230V to 24V volt transformer and put their output windings in series to get 36 volts.

 

Hello,

@#12,

The OP is talking about the rectified and buffered 240 Vac to 330 Vdc.
He would need a transformer from 240 V to 24 V ac.

Bertus

 

Sorry. Sometimes I make an outright mistake.

 

vicorpower have a range of dc to dc conversion modules.

Timescope

 

I made one such supply, using a Power Integrations IC, and a self-made ferrite transformer. Which I did not measure or calculate, just added an amount of wire that looked reasonable.

Fine magnet wire for the primary, one layer, then electrical tape, and thick magnet wire for the secondary.

It worked!

The LNK302 etc chips can be used for transformer based supplies (allowed on the forum), as well for offline supplies (not allowed here). See pictures.

For 330V AC use a transformer, unless you are an expert on the subject with years of experience.

If you only have 80V or 90V AC, use a offline supply, it is cheaper, everything is smaller, you can even use a RF inductor.

They are not rated for grid voltage I think.

This is what expert knowledge means. you have to know all the aspects of high voltage circuits. There are many beginners here, and if everyone gives advice + threads are created, it is only a questions of time until accidents are caused from advice gained here and circuits found here.

The best: Buy a ready-made supply. Even if you could make one yourself.
You really must have reasons to build one yourself (for instance because it is smart for your purpose).