At 12:39 PM 12/03/2010, you wrote:
>Hi, List.
>
>I am working on a mixed signal system and I need to generate a smallish
>negative voltage, (say -1V or so) for use as a negative op
>amp/comparator supply to overcome problems like comparators not swinging
>to ground, etc.
>
>In the past, I have used ICL7660's or National LM2687, both work well;
>solid enough and quiet enough, but they seem like overkill....does
>anybody have a favorite, simple solution for something like this?

Not exactly practical in most cases (not much output current available,
requires high input voltage & power), but there's this simple & cheap one:


               +12VDC              eg. 2N4401
                  +       E    C
                  |  ___
                   -|___|- -   -  output (-300 ~ -400mV)
                            ^ /
                     1K     ---
                             |
                             |
                            ===
                            GND


Don't bother trying to SPICE it.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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