LED high-current circuit not shown.
Batt+ Batt-
|--| |-----|
| |----*<--Rled---| (tail cap LED,shorted by switch)
| |---------/ ----| (tail cap switch)
| |
| |
|---------BR----------------| (case ground plane, not equal to
| | batt- when tail cap led is on)
R5 |
| C1 |
|---------------||----------|
| |
|-------R1----------R2------|
| | |
| Vsense pin |
LDO---- |
| |
(Schottky) V |
| |
| |
|----------mcu---------|
|--------<(zener)------|
Vcc |----------||----------|
C2
(Generally either the LDO or the zener or neither will exist but not both at once.)
or for reference, it can be found here: https://budgetlightforum.com/t/-/44344#TAcircuit
But I added the Rled in the version above, in the way I >>believe<< it's wired (pretty sure, but never saw one).
Separated? The only way Bat+ is getting to Rled is through BR and in parallel also through R1/R2. That's current, through the divider resistors. Current on a resistor = voltage. (also through R5, but that's tiny) Yes, the mcu itself is on a completely isolated circuit. The mcu power circuit, once the switch is off has nothing to do with the BR-R1-R2-Rled circuit. The voltage for shutdown detection is not the C2 voltage, it's the C1 voltage, but more specifically the C1 voltage divided through R1 and R2.