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:
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
