Electronics > Beginners

Generating 3 voltage rails, will this work ?

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BravoV:
The +15V and -15V rails are classic topology, linearly regulated to power the analog section, while the +5V rail uses an isolated DC to DC step-down switching converter to power logic parts.

Will this work ? Other considerations if any ?

Thanks in advance.

Ian.M:
It will work, but a fully regulated isolated DC-DC converter is more expensive than a simple switching (non-isolated buck) regulator run off the unregulated +V rail.   

If you need a *LOT* of current from the +5V rail, you may have to go with the isolated DC-DC converter to utilise the whole secondary, but as high current isolated DC-DC converters are expensive, its probably more cost-effective to simply up the mains transformer VA rating and use a simple switching regulator.

CJay:
I've just done pretty much exactly that to remove the need for a custom mains transformer.

Using a centre tapped mains transformer to feed 7915 and 7815 regulators and 'stealing' some power from the positive rectifier to feed a buck converter (no need for isolation in my application) for a 5V rail.

Benta:
I've done it the "other way round". A 5 V wall-wart to power the logic, and an isolated 5 V in, +/-15 V out DC-DC module.

BravoV:

--- Quote from: Ian.M on June 29, 2018, 09:33:29 am ---It will work, but a fully regulated isolated DC-DC converter is more expensive than a simple switching (non-isolated buck) regulator run off the unregulated +V rail.   

If you need a *LOT* of current from the +5V rail, you may have to go with the isolated DC-DC converter to utilise the whole secondary, but as high current isolated DC-DC converters are expensive, its probably more cost-effective to simply up the mains transformer VA rating and use a simple switching regulator.

--- End quote ---

Thanks for the confirmation.  :-+

Yeah, the +5V rail needs about 4 to 5 Amps while the pos & neg 15V rails only merely at sub 100mA.

My situation is I already have a suitable transformer with the right size, its just its only has 3 taps includes the CT.

Also coincidentally at local here there is a really cheap offering for a NOS Vicor high density DC to DC module that I think suitable for +5Volt rail.

Yeah, buying a new one of this isolated DC to DC is very expensive.

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