Electrical – Stm32f103 blue pill and stlink power


When two or more of these modules have their 5v pins hooked up to a common 5v rail (power off) and I connect an 4-pin SWD st-link to the programming pins of one, I'm finding that all modules (and peripherals attached to them) power up. In other words, the 3v3 from the st-link is powering everything. The voltage on the rail is 2v6. Would it be better to have a diode between the 5v pin of each module and the 5v rail? Thanks for your thoughts.

This shows both the mcu board and the swd st-link board:


Best Answer

3V3 on SWD is intended as a target supply sense. Probably it has some current-sourcing capability, but it's rather limited (hence you see the voltage drop to 2.6V).

As Chris suggested, you shouldn't connect programmer to powered-off board. You could try to add diode there, but I'm not entirely sure, how programmer will deal with the diode voltage drop - it could assume, that voltage rail is at level insufficient for reliable operation and refuse to program.

As for putting a diode on power supply lines of each of boards, an LDO probably wouldn't hurt much and prevent current flow back into power rail.