Another role for it would be to limit the inrush currents. More than that let's not forget that we have 2 power supplies here and when the lights go on the first supply(flyback) input gets shorted by the relays contact(I have the relays variant btw not the one with triac) so I'm thinking that other transients appear here as the primary inductor doesn't like that as far as I know - so I assume the above mentioned resistor of 100Kohm comes into play here too. I know that there are other solutions to overcome the transients but they are either bulky or too slow for this(correct me if I'm wrong here). Now the only purpose that I imagine for this resistor is to suppress the transients - but it has a big value(100Kohm) which limits the current to a non-usable value for our purpose. From time to time the switching transistor(mje13003) burns out and this is because I removed the resistor placed at the input of this power supply - near the bridge rectifier and replaced it with a wire(this is not the same resistor as replaced from the base of the transistor which is the startup resistor for the flyback converter). I tried various combinations using sleep schemes and to change the flyback converter components as other mentioned in the mysensors forum and indeed I can power up my custom design that is presented in this thread BUT it's NOT STABLE. I'm not a switching power supplies expert here(even though I want to learn more about SMPS's in general but my time is limited for now) but I've come to a conclusion: it's difficult to tune this or to change the existing circuit to accommodate the mysensors circuits power requirements.
But all of this comes at a cost: it's difficult to obtain a stable circuit and it has to be tuned by trial and error - at least this is what the literature says. Indeed it provides the most compact solution for space constrained designs. I studied a little bit more this part of the circuit and it's a standard self oscillating flyback converter or a ringing choke converter as others call it.
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