How to make -18v

[hecmac]

ive got between 3-5v in and I need to create -18v at around 0.7 watts. How do I go about this, do I simpily boost it up to 18v, with a boost converter ic, then connect the gnd and vout backwards, or do I need an ic that outputs -18v instead? Thanks in advance!

 

[(*steve*)]

Probably the latter unless you have a DC to DC converter with an isolated output. Most of the cheap devices are not isolated (they typically have a common ground).

 

[Bluejets]

There are dc to split output converters available but not at -18v.

https://www.ebay.com.au/itm/Mini-DC...hash=item41ecf1142a:m:mS-3LiXteuGHEEBa-9zZO3Q

 

[hecmac]

I doubt that I will actually need -18, probs a bit of leeway, 15v may work, however id assume that the chip isn't exactly efficient at lower input voltages. cant find anything on this chip though, don't even know what it is! xD

 

[Bluejets]

however id assume that the chip isn't exactly efficient at lower input voltages

Not sure how you came to this conclusion.