Mine has a LM78 regulator, but it's the same difference. I'm really lacking the analog/psu expertise here, so I'm wildly hypothesizing. If anyone knows better, please chime in, I'd like to know too.
I think the SOT-23 could be a zener diode (one terminal NC) and it's part of the back EMF protection for the LDO. Another wild guess based on the marking on mine is it's 7.5V. This means that the LDO actually runs from ~14V instead of the 22V-24V input voltage. There are caps close to the LDO on both the +22V rail and the LDO input, with the zener in between. If the coils happen to pull the +22V during the switch the 7.5V separation between the power rails enable the first cap to discharge more while the second cap is keeping the LDO input stable. Maybe this is needed because the logic can be easily made to false trigger on any disturbance on the +5V and the PSRR of the LDO itself is not enough to do that.
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