Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
Use a switch mode regulator to generate it, I seem to remember the MAX774 being a -5V generator. Depending on what you are planning on doing it may be advisable to follow the output with a 7905 linear regulator
If it simply an op-amp then simply a virtual ground!
Have a look at DC/DC charge pumps converters ..
Pretty common configuration is Vout= - Vin ..
LM2662/3 will deliver -5V @ 200mA when supplied of +5V ..
MAX660 --> -5V @ 100mA
ICL7660(MAX660) --> -5V @ 20mA .. and so on ..
You can also consider generating -5V from +9 to +12V with 555 timer (see picture below, both diodes 1N4148, or similar)