> I am trying to design a dual rail power supply for a photo diode detector.
>
> I don't want to use those dual output switched mode power supply modules
> because they tend to have a lot of ripple. Anyone disagree?
>
> I my solution is to use a switched capacitor voltage inverter chip
> followed by a -ve linear regulator for the -ve supply.
>
> I am having problems finding:
>
> 1.   LDO -ve linear regulators and
> 2.  surface mount switched capacitor inverters that can accept more than
> 5.5V input with > 50kHz switching freq.
>
> Anyone tell me how it should be done?

If your ultimate source of power is AC, you could build a linear supply.

But really you don't need to worry about the negative supply, it doesn't
even need to be regulated unless you are doing something special.

Also, your opamps do have a spec for their power supply rejection, if it
is good enough, don't worry about it. The photodiode supply is another
matter - if you are doing it the standard way, tying one end of the
photodiode to a supply and the other end to the inverting input of an
opamp, then the photodiode capacitance can couple some supply noise to the
opamp. But since the photodiode is a current source, the exact voltage you
bias it with is not important, and you can RC filter the photodiode
supply.

Cheerful regards,

Bob



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