Voltage selector, auto voltage regulator

[marcelomd]

Hi,

The next thing I want to do with my dual channel preamp (I swear I'll stop talking about it... someday...) is to integrate it with a class D power amp like the cheap TPA3118 based modules you see around.

I want to put the pre- and poweramp in the same box, but I want to retain the ability to use the preamp standalone. The thing is the preamp is 9V and the power amp goes from 4.5V to 24V.

I COULD put a buck/boost there and feed the preamp from it, but I'm scared of the noise.

So I thought about an automatic power router. Anything under 9V passes through, and anything above goes to a linear regulator.



EDIT: Never mind the specific components... they were the first I found that make what I want.

Any comments?
Am I missing something?
Am I being dumb and should do a buck/boost anyway?

Thanks!

[Rob Strand]

If you use a linear regulator set to 9V output the output will sort of track the input anyway.  When the input drops below 9V + dropout_voltage the output voltage is Vout = Vin - dropout_voltage.   A linear regulator does what you want.   You can use lower dropout regulators for less loss.    Things like the 1.25V 3-pin regulators will work down to a reasonably low Vin.