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Very wide range isolated DC-DC converter

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Doctorandus_P:
Have you considered a switching pre-regulator?

With that you can get your wide input voltage down to a somwhat stable voltage, and then use a standard  isolated DC-DC converter to get to the 3V3 output.

I might have missed it, but how much current do you need at the 3V3 output?

Or else go tell your customor that if they want a non standard power supply with a very wide input range and other strict demands (efficiency, size) that it is not going to be cheap.

forrestc:

--- Quote from: jbb on January 19, 2019, 08:24:10 pm ---I hate to be a party pooper, but this looks like an ill-defined and challenging space.

--- End quote ---

Oh you're not telling me anything I don't know.  This is what an industry which has grown up over 20+ years and no power standards looks like.  It used to be much worse, with the end equipment needing all sorts of random voltages (one would need no more than 12V, one would need no less than 12V, another would need 18V nominal).   Fortunately it's consolidated around 12, 24 and 48V lead acid battery voltage ranges which make things somewhat easier.


--- Quote from: jbb on January 19, 2019, 08:24:10 pm ---If you want to persist with the high efficiency + super wide range approach, then the best result might be found using a non-traditional converter. For example:
- polarity can be inverted from -48V to + 48V using a switched capacitor converter at fixed duty cycle and frequency. Sure the output won’t be regulated, but the subsequent buck can fix that.
- multilevel converters can offer a more reasonable way to work with high conversion ratios and still have reasonable duty cycles (eg a Flying Capacitor converter)

--- End quote ---

This is largely what I do today (see schematic 1 I posted).   I have a +9-48VDC range DC-DC converter design I've been using for years.   When we needed to add the -48VDC I added a neg to positive inverter using a linear technologies part.   It happens to output +12V but there's no reason it couldn't be pretty much any other voltage (or unregulated).

I'd love to find a simpler/lower cost design for the negative to positive supply, which should be doable since the negative rail is much tighter range than the positive side - it really only needs to support something like -36 to -60V, which is the normal range for a lead acid battery array.

Doctorandus_P:
Have u thought about using a single diode instead of a full bridge?

Why make 120V out of it if the max input is + / - 60V?

What kind of frequencies do your input voltages have?
A viable method is to put a fet on the input and simply turn the fet off if your buffer elco is charged to a certain voltage.
This can greatly reduce the input voltage range required, and as noted earlier:

Isolated DC-DC converters with an 1:4 input range are readily available off the shelf products.

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