aman said:
I have seen in some analog circuits that if we need a 2.5 V supply
there is way to do it that generate a 5V square pulse with duty cycle
1/2 and pass it through a low pass filter to get a DC 2.5V.
This method has problems with additional voltage drop through the low
pass filter when the load on the 2.5 volt output uses current.
I was thinking of another way of generating 2.5V. Use a voltage divider
and then use an opamp buffer.
As long as the load doesn't upset the opamp (less current than its
output can deliver without current limiting, and capacitance to ground
that does not make the buffer unstable) this can work fine. You can
also add a capacitor from the divider output to ground to clean up any
high frequency noise that was present on the 5 volt supply. The 2.5
volt output will be less accurate than the 5 volt supply (must include
divider tolerance and drift and opamp offset voltage).
Which of the above 2 ways is a recommended way of generating 2.5V DC?
I prefer the second for most low current needs. There are also fixed
and adjustable regulators that are made for this sort of thing.
For example:
http://www.national.com/ds/LM/LM117.pdf
http://www.national.com/ds.cgi/LM/LM4140.pdf
http://www.national.com/pf/LM/LM4120.html#Datasheet
These may improve on the voltage accuracy of the 5 volt supply.
If the load current is more than a few tens of milliamps, you may want
to look into a switching buck regulator, because of its higher efficiency.