Re: can single input DC 18v~34V to get +5 and +-15V DC outp
Because of the wide input voltage range I would use simple switcher step-down voltage regulators (for 1A/5V see picture below).
Again, if 1A @ 15V is enough, LM2575-ADJ ( **broken link removed** .. page 12 ) can be the choice, and for negative voltage see inverting regulator (page 20 of the PDF) ..
For 3A current load see: **broken link removed**
For 5A see: **broken link removed**
and so on ..
Regards,
IanP