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Dreken

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  1. I have tried to build my first project (modification of existing one) and would like to to have few questions to the design. Last time I was doing something it was in the times without PC's so most probably my drawings are not correct. Very first point is about slow start of power source I have the main tranformer T1 and support one T2, T2 creates +- 5V to the + of main transformer (more or less for simplification). The idea of slow start is to bridge the 2 resistors by relay (MRE1) as soon as MC1 (YELLOW) is charged. All calculations are made to limit startup current to ~10A, for capacitors ESR 0.012 is used. How I tried to do it is that MT1 monitors voltage drop on charge resistor MR7, by drop >0.7V the MT1 keeps open, meaning MT2 base is shortened with MT2 emitor so MT2 is closed, by drop <0.7 MT1 closes allowing MT2 to open and bring voltage to relay which shortens the slow start resistors (MR2+MR7). Then I recognized following issues: Missing indication LED so I have added them (MD1 for charging and MD2 for charged), but pas MD1 is in series it causes voltage drop that is not welcomed and I did not manage to sort it out, also I believe that current thru MD1 will be too small to light the led (I have calculated 0.1mA). Also MD1 should work in range of voltage from ~61V (power on time) until ~5.7V (relay turn on time) and I do not know how to calculate the resistor for this voltage range (have seen some circuit with 2 transistors instead of resistor but can not understand it) On the relay coil is only 5 volts (connected between +5 and 0), but as there will be still quite big current in the switchover moment I would like to use 12V relay (that is made for higher currents) but for this I need at least 10V (so +-5 connection will be OK), but for some reason that I can not understand if I connect emitter of MT2 to -5 it did not work (in simulator) as there is some kind of current that charges MC1 from the +5V and that is BAD I wanted to compensate for point 2 by delaying MT2 turn on by MC2, but before MT1 closes it goes thru active area and pre-charges MC2, where by calculation I have 5 seconds but simulator says 2-3s I'm not sure about all the resistors named MRx and basically all components starting with M (indicated that it is Modified/new part of the circuit) as these resistors and other elements I have calculated (blue) The relay protection circuit (MR1+MD7) is copied from some web page, but have absolutelly no idea on diode type and resistor value (so most probably wrong again) Does anyone can help with the design? In case of other damage of the circuit, I also read something about LED circuit protection
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