11-15V to drive 2N3904 base

dephwyggl:
why are we having to manage that much heat with a 3-7V drop and .25A if the Nano's internal regulator (AMS1117) can manage a 2-7V drop and .5A without a heat sink?

It can't.
The 1117 is a lineair regulator, just like the 78xx.
All lineair regulators convert voltdrop into heat.
One watt is pushing it for the 1117 when mounted on a circuit board (= heatsink).
So 2volt difference at 500mA might just work (stinking hot).
The 78xx can manage >10watt when mounted on a proper heatsink.

Only a switching supply can drop the voltage with little or no heat generated.

Buck converters like this can take 12volt/100mA, and change it e.g. into 5volt/200mA.
Leo..

Wawa:
It can't.
The 1117 is a lineair regulator, just like the 78xx.
All lineair regulators convert voltdrop into heat.
One watt is pushing it for the 1117 when mounted on a circuit board (= heatsink).
So 2volt difference at 500mA might just work (stinking hot).
The 78xx can manage >10watt when mounted on a proper heatsink.

Only a switching supply can drop the voltage with little or no heat generated.
Pololu 5V, 500mA Step-Down Voltage Regulator D24V5F5
Buck converters like this can take 12volt/100mA, and change it e.g. into 5volt/200mA.

Thank you for the explanation, Leo. It's starting to make sense to me. I was starting to already think that maybe the only way to mitigate heat generation (i.e. increase efficiency) is to go to a switching type regulator. I already have a few of these but was hoping to get away from needing a separate "board", and, at least in this project's case, don't need adjustability. I was hoping to be able to mount something directly on the PCB with the rest of the project's circuit. Maybe - at least for version 1 - I'll stay with the L7808CV arrangement.

PS Though ideally there'd be a 7V version of Pololu's regulator, but they do have a 9V version. Just a bit pricey for this (stage of this) project.

Again, thanks tons for all your help and suggestions, Leo. Learning a bit every time... :slight_smile:

Working on niggly details and will post a link to a new topic with the whole circuit and - very likely - tons more questions. :grin:

Dirk

A 5volt/500mA switching supply can be as small as an 78xx, and won't need a heatsink.

Anther option is to go directly to 5volt, and feed that into the 5volt pin of the Nano.
Possible now you have moved the diode to the input side of the regulator.
Leo..

HI all,

This stage of this project is complete. I'd like to extend my deepest gratitude to everyone who's helped get me to this point - in particular, to better understand the elements (power supply and Arduino switching considerations) of this topic.

This project is now moving on to the development of the output stages.

Cheers!
Dirk