Negative voltage in circuit

[Vindhyachal.takniki]

I need negative voltage in my circuit with common ground wrt positive voltage

1. One option is to generate negative supply by placing a full- bridhe & then using 7905.
It includes lots of extra components to be used.
2. Another option is to use TC7660. Simple to use & works good. Only problem is its output voltage falls with current. For a load current of -10 mA and a supply voltage of +5V, the output voltage would be -4.3V.

3.I need to generate regulated -5V,-2.5V&-1.8V

4.Any other way to do that?

[kg4arn]

What is the current demand for each negative supply?

[Vindhyachal.takniki]

50mA max.

[electr_peter]

How do you power your circuit? If you have spare transformer tap, use that.
Other option would be inverting DC/DC voltage inverter. There are also isolated DC/DC 5V in/5V out converters (at a higher cost of course).

[IanB]

If you are powering your circuit with low voltage AC from a transformer then can't you just rig up a voltage inverting leg off the AC source? (I think it only needs a couple of diodes and a couple of capacitors. Both are cheap jelly-bean components.)

[mariush]

If you don't want to complicate your life with multiple taps on transformer, you could also resort to using a cheap mc34063 switching regulator in inverting mode :  http://www.intusoft.com/onsemipdfs/AN920-D.pdf

There's a software on Sourceforge which makes the math super easy: http://sourceforge.net/projects/mc34063uc/