Fix 5V from an unstable 6v to 32v maximum DC input.

Good day!!

I am designing a charger circuit, in which the raw input is varying from 6V to 32VDC.

For the charger circuit to work, there is no problem since I have a DC-DC converter at the front end to ensure that the charger circuit is receiving a constant DC volt of 20V. I have tested both the DC-DC Converter & the charger circuits.

There are few requirements that need me to put few comparator circuits in my design. However, I doubt that those comparator circuits could work properly as the DC input is unstable. I need to have 5V DC for all the comparator circuits (& 2.5V reference V).

Is it CORRECT if I put the LM431 to generate the 5VDC from unstable input that varies from 6V to 32V ? or LM317 ??

Please, I need the ideas.......

Depends on how much current you need to draw from the reference, and how much power you are willing to waste in the regulator/series resistor. 6Vin to 5Vout is below the dropout voltage for a LM317.

You may get by only providing a fixed reference voltage of 2.495V (the natural LM431 output) to the input of your comparitor. There is no need to regulate the V+ for the regulator. Look up the Power Supply Rejection Ratio (PSRR) on the data sheet for the comparator you plan to use.