I've got a component within a larger device that requires both +15 and -15V, drawing about 100mA per rail.
In addition, the main power supply of the larger device is providing +/- 28V, with a common ground.
My initial thought was to use good old linear regulators – 7815 for +15 and 7915 for -15. However I want something a little more efficient…
…and it just so happens I have a bunch of these fancy R-7815-0.5 switching regulators (PDF) by Recom. They accept 18-35V on the input, and produce +15V on the output (500mA). In addition, they can be used to convert positive to negative, albeit at a lower output current (200mA).
I want the +28V from my supply to step down to +15… no problem there, one of the Recom devices will work perfectly. In addition, it makes sense to me that the -28V be stepped down to -15V.
However, I can't determine whether a switching regulator like this can be wired up to accept a negative voltage input, and thus produce my desired negative output voltage. To be clear, I don't want to do any voltage conversion – I want to my input +28V to produce my +15V, and my -28V to produce my -15V, to ensure that approximately the same load is being placed on both my + and – supply evenly.
In the world of compact, all-in-one switching regulators, there don't seem to be "79xx" equivalents which would make this easy!
- Is it possible to do this with the devices I have – i.e. wire the
R-7815-0.5 to accept a negative input? - If not, what would be the best way to efficiently produce +/-15V from my supply, placing an even burden on each +/-28V rail?
Best Answer
I've been using Recom converters before, really good devices. I don't think you can wire this one to draw power from negative rail, though.
So, if you want to use this particular device you'd have to draw from positive line only.
However if you open to try other Recom products, you can get any isolated dual 15V output part that accepts 56V, like RS3-4815DZ-H3, and connect input between the rails. So, you'd only need one converter and no other parts.